The following is a list of the abstracts for papers which will be presented in FIFTH INTERNATIONAL SYMPOSIUM ON CONTACT ANGLE, WETTABILITY AND ADHESION. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)
Tanweer Ahsan; Henkel Corporation, 15350 Barranca Parkway, Irvine, CA 92688
Adhesion Performance of Molding Compounds in Semiconductor Packaging
Plastic packaging of integrated circuits (ICs) requires adhesion solutions to many surfaces. These include die passivation layers such as SiO2 and SiN3, bond pad areas, polymers and metal surfaces such as copper, Nickel, gold and aluminum. Recent development of molding compounds to meet the recommended JEDEC (Joint Electron Device Engineering Council) standards has placed great demands on formulators to offer competitive materials for optimum performance.
This overview will include the importance of clean surfaces for optimized performance of molding compounds on ICs. Use of enhanced adhesion technology along with surface diagnostic techniques such as contact angles and surface energetics have led to the development of new and improved materials. Surface acoustic micrographs (SAM) show that adhesion of molding compounds to various die passivation layers is different. However, for reproducible performance, Ar plasma etched surfaces have shown to respond favorably irrespective of the type of die passivation. The most likely explanation is the wettability improvement and decontamination of the die surfaces due to Ar-etching which in turn gives better and reproducible adhesion.
A.Milne, W Li, K. Grundke and A. Amirfazli; Department of Mechanical Engineering, University of Alberta, Edmonton, AB, T6G 2G8
Wetting of Superhydrphobic Surfaces: Experimental and Theoretical Perspectives
From theoretical perspective, a free energy thermodynamic analysis is used to determine equilibrium contact angle and contact angle hysteresis (CAH) for microtextured surfaces with pillar structure, typical of one used in experimental studies. We demonstrate that the predicted CAH and equilibrium contact angles are consistent with experimental observations and predictions of Wenzel and Cassie equations, respectively. We also establish a criterion for transition between noncomposite and composite wetting states. The necessity of a dual-scale roughness to produce practical superhydrophobic surfaces will also be discussed.
On the experimental side, the effect of surfactants on wetting behavior of ultrahydrophobic surfaces will be discussed. Contact angles of different surfactants (SDS, HTAB, MEGA 10) on three different superhydrophobic surfaces (AKD, Al oxide, and roughen PTFE) will be presented. For all systems the usual behavior of ultrahydrophobic surfaces that turn ultrahydrophilic when the intrinsic contact angle of liquid on a smooth surface (of identical material) is below 90 degree was not observed in presence of surfactants. Depending on the surface chemistry and roughness the CAH behavior was different, i.e. for AKD surfaces it remained constant, but for other two surfaces with progressive increase of surfactant concentration, it unboundedly increased. The droplet dynamics implementation of these observations will be discussed. The results and methodology presented can potentially be used for designing superhydrophobic surfaces.
Thomas Bahners1, Lutz Prager2 and Eckhard Schollmeyer1
1) Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY
2) Leibniz-Institut für Oberflächenmodifizierung e.V., Permoserstr. 15, 04318 Leipzig, GERMANY
Functional Top Coats on Coated Textiles for Improved or Self-attained Cleanability
Highly hydrophobic finishes are of increasing importance in the field of technical textiles, e.g. for improved or even self-acting cleanability. The hydrophobicity of a surface is defined by the involved boundary potentials, the important factor being the relation of the loss in surface energy due to the spreading droplet and the energy increase due to adsorption. Minimum total energy defines the equilibrium of the system. Besides the introduction of polar groups, the introduction of a micro-roughness to the surface is proposed by many authors as a means to increase the overall fluid repellence. With regard to textiles, a number of surface modifications have been described in this context. A drawback for many technical products is that all proposed processes refer to the actual fiber surfaces and are not necessarily applicable to the important class of coated textiles.
One exemplary application of coated textiles is the construction of textile roofs in modern architecture, where easy or self-attained cleanability is highly demanded. Today, hydrophobic top coats, i.e. lacquers of approx. 5 Ám thickness, are already applied to coated fabrics, but do not act sufficiently. The aim of the presented work, therefore, was to study the effect of an additional micro-roughness of these coats. The micro-roughness was achieved by a two-step process where UV irradiation with < 200 nm was used for the cross-linking of an ultra-thin surface layer, while the bulk of the lacquer was cured consecutively at longer wavelengths. Following shrinkage processes a rough surface is obtained ('micro-folding'). An overview is given over the obtainable surface topologies, their effect on contact angle and on cleanability.
Bernt Boström, FIBRO System AB, Stockholm, SWEDEN
Evaluation of Very Low Contact Angles Using a Compact Video System
Contact angle measurements have become an established method to determine surface properties critical in most wetting and spreading applications. The currently available instruments equipped with a video camera are, however, not very well suited for quality control (QC) purposes as they were originally designed for laboratory work carried out by advanced scientists. Apart from being bulky and fragile the use of a specimen stage is often a severe limitation as the preparation of a sample in itself can often introduce contamination of the tested surface.
Ideally, a small, fully automatic measuring head that can be operated by "anyone" and placed on top of any reasonably flat surface would be preferred in most QC applications. The design of a small, compact instrument will, however, require special considerations with regard to the optical system and the droplet application. Because of the short viewing distance, there is not enough space for a complex lens system. Another requirement is the measurement of contact angles below five degrees, which is neglected in most of the commercial instruments. Traditional tracing of the droplet contour will fail for these low contact angles as the top of a sessile drop becomes invisible to a video camera equipped with a small standard lens.
This paper describes the phenomena that occur in a compact low-cost system for static and dynamic contact angle measurements on a sessile drop.
Laurence Boulangé-Petermann1*, Christelle Gabet1, Jean Charles Joud2 , Bernard Baroux,2
1) Ugine-ALZ, Arcelor, FRANCE
2). INP Grenoble, FRANCE
* Current address : Becton Dickinson, Pont de Claix, France
Effect of the Surface Properties on the Cleanability of Bare and Coated Stainless Steels
Cleanliness of steel surfaces is a commonplace in food or catering industrie, medical applications, etc... Attention is paid in this talk to the physicochemical properties which control both soiling and cleaning ability of a metal surface, taking into consideration the different mechanisms involved in the most current cleaning processes. Examples are given for some stainless steels bare or coated surfaces.
First, when the surfaces are mechanically cleaned using a flow of liquid (e.g. water) a correlation of the surface cleanability and the hystereris of the water contact angle is evidenced, which can be discussed in terms of surface chemistry or microgeometry. Secondly, oil removal by a surfactant containing aqueous solution is shown to be strongly related to the polar component of the surface energy: the higher the polar component was, the easier the oil removal. Finally, examples are given of the effects on the surface soiling of some surface microgeometries favouring oil impregnation. Last a new experiment is presented, aiming to understand better what happens during the removal of an oil droplet, and opening the route to further modelling of cleaning mechanisms.
M. G. Cabezas,1 M. Hoorfar 1, H. Tavana 1 and A. W. Neumann2;
1) Escuela de Ingenierías Industriales, Universidad de Extremadura, ESPAÑA
2) Department of Mechanical Eng., University of Toronto, Toronto Ontario M5S IA4, CANADA
Axisymmetric Drop Shape Analysis (ADSA) For The Determination of Contact Angle
Considerable progress in contact angle measurement has been made by the use of image analysis based on analysis of drop shapes in combination with integration of the Laplace equation of capillarity. One such method, called Axisymmetric Drop Shape Analysis (ADSA) has been used extensively for this purpose. One remaining difficulty is the exact determination of the point where the meniscus intersects the solid surface. It will be shown how this problem can be solved by fitting a carefully selected polynomial to the reflection of the drop near the solid surface. The possibility of fitting a short section of the actual drop edge to a polynomial will also be explored, in order to clarify the question of relative merit of the global fitting by ADSA compared to the local fitting to a small section of the meniscus near the solid surface. Illustrations and examples will be presented and discuss.
P. J. Ramón-Torregrosa1, M. A. Rodríguez-Valverde2 and M. A. Cabrerizo-Vílchez1
1) Biocolloid and Fluid Physics Group, Applied Physics Department, Sciences Faculty, University of Granada. E-18071 Granada, Spain, firstname.lastname@example.org
2) Polymers and Composites Laboratory, Dept. of Materials Engineering and Industrial Technologies, University of Trento. E- 38050 Trento, Italy
Effect of Acid-Etching on Titanium Wettability. A Crossover Between Wetting Regimens
Titanium oxide (rutile) is widely used for industrial applications. In particular, titanium is the basic material of many medical devices. In this field, implants require different surface treatments to assure the biocompatibility, i.e. the cell tissue growth. A first requirement for cellular adhesion on biomaterials is the surface roughness and this can be controlled by different means. Acid-etching is an extended method in dental implants although the etching time is a critical parameter. A second requisite to osteointegration is the suitable biomaterial wettability by the internal physiological liquids. The challenge is to find a trade-off between roughness and wettability.
Nine sets of there titanium disks (diameter=, thickness=) were etched by fluorhidric acid. Each set was attacked for different times, from 15 to 750 s. Topographies of each sample were achieved by AFM using Tapping mode and the Wenzel factor and fractal dimension were used as roughness estimators. A peak in the roughness is observed at 200 s.
Contact angles were measured using the sessile drop method and the technique Axisymmetric Drop Shape Analysis (ADSA). Simultaneously, top and side views were acquired for each drop and two values of contact angle were computed by ADSA-Profile and ADSA-Diameter. A modified Wenzel equation including a texture parameter was fitted in the range before the roughness peak. After this peak, the wetting changes of regimen.
Financial support from "Ministerio de Ciencia y Tecnología, plan nacional de Investigación Científica: Desarrollo de Investigación Tecnólogica (I+D+I)" project MAT2004-06872-C03-01 is gratefully acknowledged.
F. J. Montes Ruiz-Cabello1, P. Gea-Jódar1, M. A. Rodríguez-Valverde2 and M . A. Cabrerizo-Vílchez1
1) Biocolloid and Fluid Physics Group, Applied Physics Department, Sciences Faculty, University of Granada. E-18071 Granada, SPAIN
2) Polymers and Composites Laboratory, Dept. of Materials Engineering and Industrial Technologies, University of Trento. E- 38050 Trento, ITALY
Contact Angle of Polygonal Sessile Drops
Status quo in the field of interfacial techniques aimed to wetting phenomena, in particular the sessile drop method, follows on being limited to approximations as consider the drops as spherical caps and axisymmetric shapes. With these approaches, one only side view of drop is required. Unfortunately, the most interesting solid surfaces usually exhibit a moderate heterogeneity and/or roughness and therefore, the formation of non-axisymmetric drops on them. This asymmetry )involves a multiplicity in contact angle defined by more than a simple mean value.
Simultaneous acquisition are proposed of top and side views of the sessile drop. From two or even three images we can characterize the wetting of a drop using an average contact angle and the extremes values of contact angle. Axisymmetric Drop Shape Analysis-Diameter (ADSA-D) and Axisymmetric Drop Shape Analysis-Profile were used to analyze each drop images. This approach was tested by simulations with Surface Evolver software, which allows to obtain the complete range of local contact angles from the same input parameters than ADSA-D.
We used acetate surfaces with different heterogeneous patterns obtained from a high resolution laser printer. White light confocal microscopy was used to characterize the topography of these surfaces.
Financial support from "Ministerio de Ciencia y Tecnología, plan nacional de Investigación Científica: Desarrollo de Investigación Tecnólogica (I+D+I)" project MAT2004-06872-C03-01 is gratefully acknowledged.
Alain Carré and Valérie Lacarrière; Corning European Technology Centre, 7bis avenue de Valvins, 77210 Avon, FRANCE
Cell Adhesion And Proliferation on Polystyrene Substrates of Different Surface Properties
Cell culture has become one of the major tools used in cell and molecular biology. Most cells derived from solid tissues require an adherent surface to live and proliferate in vitro conditions. A good understanding of the relationships between the behavior of cells and the physicochemical properties of the substrates such as the surface free energy, the presence of functional groups and surface charges, is of prime importance for the optimization of adhesion, spreading and proliferation of cells.
Polystyrene and plasma treated polystyrene surfaces were characterized by measuring the polar and non-polar components of the surface free energy of the substrates by using a wettability technique. The method consists of measuring the contact angles of polar and non-polar liquid probes. Then, the adhesion and proliferation kinetics of cells (Human embryonic lung fibroblasts, Chinese hamster ovary cells) were quantitatively studied on the polystyrene surfaces. The percentage of adherent cells, the exponential proliferation rate constant and the doubling population time were quantified on the different polystyrene substrates.
During the adhesion step the cells spread on the substrate. This is a crucial step that precedes the exponential proliferation of cells. In presence of bovine albumin serum, it is shown that the adhesion of cells increases with the polar contribution of the surface energy. The situation is different in absence of serum, demonstrating the important impact of the adsorption of biological compounds (proteins, other compounds) on the adhesion of cells on solid substrates.
Emil Chibowski, Konrad Terpilowski and Lucyna Holysz; Department of Physical Chemistry-Interfacial Phenomena, Faculty of Chemistry,Maria Curie-Sklodowska University, Lublin, POLAND
Influence of Ambient Humidity on the Apparent Surface Free Energy of Smooth Solid Surface
Wettability of a solid surface by a liquid is governed by chemical properties and structure of the surface and surface tension of the liquid. In wetting processes taking place both in natural environment and industry the surface free energy of solid and liquid, and the interfacial solid/liquid free energy, play a crucial role. To measure contact angle hysteresis 6Ál droplet was settled on the surface and advancing contact angle was measured, then 2Ál of water was sucked from this droplet into the syringe and receding contact angle was measured. The contact angles were measurement at 20░C in controlled humidity cell, between 1,5 and 100% on polymethylmethacrylate (PMMA) plates. At least 20 contact angles were measured at each value of humidity. Then the surface fee energy of PMMA was determined from the measured advancing and receding contact angles. The energy was calculated from hysteresis approach (1-3). Thus calculated the apparent PMMA free energy generally decreases with the increasing humidity of the environment. However it shows a remarkable minimum at 15% RH (Fig.1). Similar are being conducting on silicon plates. So far water contact angles up to 65% rel. humidity are done. As can be seen in (Fig. 2) there is a maximum of ca. 30% rel. humidity. The observed changes in the energy must be due to water adsorbed film present on the surfaces.
1. E. Chibowski, in K.L.Mittal(Ed.) Acid-Base Interactions, V.2, VSP, Utrecht, 2000,p.419.
2. E. Chibowski, Advances in Colloid and Interface Science, 103,149,(2003)
3. H. Radelczuk, L.Ho ysz, E. Chibowski, J.Adhesion Sci. Technol., 19,1221,(1998)
The authors thank for the financial support from Polish Ministry of
Education and Science, Project No.3 T09A 04329.
Emil Chibowski, Konrad Terpilowski and Lucyna Holysz; Department of Physical Chemistry-Interfacial Phenomena, Faculty of Chemistry,Maria Curie-Sklodowska University, Lublin, POLAND
Superhydrophobic Effect Due to Deposition of Nano- And/or Microparticles on a Solid Surface
Superhydrophobic surfaces on which water contact angle is larger than 150o have been obtained by controlling the surface topography. Water drop on such surfaces rolls off when it is slightly tilted and thus cleans the surface. To produce the superhydrophobic surfaces different types of solid particles were used, i.e. glass spheres (11,3Ám), Teflon (922nm), SiO2 (728nm), polypropylene (100nm). The average diameter of these particles was measured by Turbiscan LabEXPERT technique. First, an optimal concentration of PMMA dissolved in chloroform to form polymer film on glass substrate was sought. The solutions containing 0.6, 0.5, 0.4, 0.3, 0.2, 0.1g PMMA in 100cm3 of chloroform were prepared. The highest contact angles of water were measured on the plates covered with PMMA film from its 0.1g/100 cm3 solution, and this concentration was used to prepare dispersion of the nanoparticles. Water contact angles on the plates covered with PMMA film from a solution at the concentration lower then 0.1g/100 cm3 were not reproducible. Then, using this optimal PMMA solution several concentrations of the nanoparicles were used. The dispersions (0.25 cm3) were deposited on the glass substrates (2 cm in diameter) using the spin-coating technique. The deposited layers were obtained at different speeds of the coater, from 18 to 45 rps. The plates were then dried at room temperature for 12 h and after that contact angles of water were measured by the syringe method using Digidrop apparatus of GBX (France). To measure the contact angle hysteresis, 6Ál droplet of water was settled on the surface and the advancing contact angle was measured. Then, 2Ál of the water was sucked from this droplet into the syringe and the receding contact angle was measured.
Figure 1. Photographs of 6 ml (a,a') and 4 ml (b,b') water droplets on glass slides coated with PP or SiO2 nanoparticles respectively by spin-coating technique at 18 rps
From the contact angles hysteresis the apparent surface free energies were calculated (1). The apparent surface free energy, for these surfaces were between 5.6 and 6.3 mJ/m2. These preliminary results show that superhydrophobic surfaces can be produced by the technique used. However, more experiments are needed to obtain better superhydrophobic mechanical properties of such layers.
1. E. Chibowski E., Adv. Colloid Interface Sci. 2003, 103, 149.
The authors thank for the financial support from Polish Ministry of Education and Science, Project No.3 T09A 04329.
S. F. Chini; H. Sadeghy, A. Milne, W. Moussa and A. Amirfazli; Department of Mechanical Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, CANADA; Study of Pattern Collapse During Photolithography of Submicron Features Due to Capillary and Surface Tension Forces
One of the major problems in fabrication of features at the nanoscale using photolithography is pattern collapse. Pattern collapse is the deformations of polymer resist patterns during rinsing process. To date the source of the pattern collapse has been identified as the unbalance of capillary pressure across the resist structures (due to uneven evaporation of rinsing liquid on either side of the resist). The capillary pressure is a function of curvature of interface as defined by the Laplace equation. In this study, it is shown that aside form capillary pressure, surface tension force is also an important factor. The surface tension force operates at the three-phase line. The contribution of surface tension force depends on the contact angle; the limits
being none when contact angle is zero to the maximum value when contact angle is 90. Model studies (a micro-cantilever
made of resist polymer) show that adding this force worsens the collapse occurrences. This study also considers a 3D model
rather than the usual 2D studies to date. Surface Evolver software has been used to determine the shape of the interface.
Note that from the shape of the interface not only the radius of curvature can be extracted to determine the capillary pressure,
but also the location of the line of action (three-phase line) for the surface tension force can be determined; additionally
contact angle variations along the three-phase line can also be determined. Findings from this 3D analysis will also be
D. Clausse , L. Sacca, F. Gomez and I. Pezron; Université de Technologie de Compiègne , Département de Génie Chimique, CNRS UMR 6067 GPI, BP 20529 - 60205 Compiègne cedex, FRANCE
Emulsions Stabilized by Nanoparticles
This work deals with water-in-oil emulsions prepared either with hydrophobic fumed silica particles or with hydrophilic silica particles modified through interactions with a cationic surfactant (cethyl trimethyl ammomium bromide). For comparison, water in paraffin oil emulsions stabilized by sorbitan monooleate have been also examined. The evolution of the emulsions versus time has been followed through the shifting of the freezing temperature of the dispersed water droplets, since the position of the crystallization peak evidenced by calorimetry, is related to the droplet size distribution and composition. Focus will be put on ripening phenomena observed in mixed emulsions consisting of pure water droplets and water droplets containing one solute (urea). Water transfers between droplets have been found to occur in all emulsions studied, the rate of transfer depending on the nature of the interfacial film. From these studies, it has been possible to evidence facilitated water transport in some cases.
This study is supported by the European Space Agency (Fundamental and Applied Studies in Emulsion Stability Project).
B.P. Binks1, J.H. Clint1, P.D.I. Fletcher1, T.J.G. Lees1 and P. Taylor2
1) Surfactant & Colloid Group, Department of Chemistry,
The University of Hull, Hull HU6 7RX, UK
2) Syngenta, Jealott's Hill International Research Station, Bracknell, Berkshire, RG42 6EY, UK
Effect of Surface Wettability on the Growth of Gold Nanoparticle Films
We have investigated the mechanism of the spontaneous growth of a gold nanoparticle film on the container wall when an aqueous dispersion of gold nanoparticles is shaken with an oil phase containing octadecylamine, as first described by K.S. Mayya and M. Sastry (Langmuir 1999, 15, 1902.). Modification of the wettability of the particles by adsorbed octadecylamine causes the gold particles to become strongly adsorbed at the oil-water interface. When the container walls are hydrophilic a gold film grows rapidly up the surface of the container above the liquids. If the internal surface of the container is treated to be hydrophobic, the gold film growth is then downwards towards the bottom of the tube. Experimental evidence is described which shows that the film growth is driven by the coalescence of particle-coated emulsion drops with the flat oil-water interface separating the oil and water phases.
Martien A. Cohen Stuart; Lab. of Physical Chemistry and Collloid Science,
Wageningen University, P. O. Box 8038, 6700 EK Wageningen, THE NETHERLANDS
Wettability of 'Soft' Surfaces: the Contact Angle on Swollen Polymer Brushes and Gels
Most experimental studies and theoretical treatments of wetting deal with simple sharp interfaces, e.g., between a solid and a liquid, or between two immiscible liquids. Many surfaces of practical importance have a more complicated, and often responsive character. In this contribution we consider wetting properties of solid surfaces carrying end-attached polymer. With respect to the liquid phase, two cases are discussed: (i) a low molar mass good solvent in which the brush can swell; (ii) a melt of polymer chains identical to the grafted ones. For case (i), theoretical calculations show that the thermodynamic contact angle can be finite, even though the liquid is a good solvent for the brush. The reason is that the polymer may often adsorb to the liquid/vapour interface. We find a remarkably simple quantitative prediction for the contact angle on dense brushes in terms of the (normalized) surface pressure exerted by unattached, physisorbed polymer at the liquid/vapour interface. Experimental data underpin this quantitatively. We also briefly discuss gels in the same context. Case (ii) leads to a variety of situations, controlled by the grafting density and the length ratio between grafted and free chains. In experiments, we find a pattern with regions of partial and complete wetting which is well accounted for by a theoretical analysis. An entropy-dominated regime of partial wetting at high grafting density has peculiar features, such as an anomalous temperature dependence.
Anton A. Darhuber, Nikolai V. Priezjev and Sandra M. Troian,
Microfluidic Research & Engineering Laboratory, Princeton University, Princeton, NJ 08544-5263
Slip Behavior at Liquid/Solid Interfaces: Hydrodynamic Predictions versus Molecular-Dynamics Simulations
The development of micro- and nanofluidic devices for channeling the flow and mixing of liquid films and droplets necessitates detailed knowledge of effective boundary conditions near inhomogeneous surfaces. Such inhomogeneities as surface roughness, chemical wettability gradients or topological patterning can either enhance or reduce viscous drag. While there is a substantial literature on drag reduction at high Reynolds number, much less is known about frictional losses and slippage at very low Reynolds number relevant to small-scale fluidic devices. Recent experiments indicate reduced frictional effects along surfaces coated with nanobubbles or surfaces consisting of hydrophobic pillar arrays.
In this talk we describe the behavior of the velocity field and slip length in liquid films flowing over patterned substrates in order to determine what geometric and molecular parameters govern the degree of slip at liquid/solid boundaries. As part of this study, we also examine what conditions or at what length scales there occurs a deviation between continuum solutions based on a Stokes flow analysis and molecular dynamics studies based on a Lennard-Jones interaction potential. Surprisingly, we find excellent agreement between these two approaches when the substrate feature size is approximately an order of magnitude larger than the liquid molecular size. Below this feature size, substrate patterns can either enhance or diminish slip relative to the continuum predictions. Further implications of these findings for flow over superhydrophobic surfaces will be discussed.
M. Brugnara, C. Della Volpe, G. Ischia, D. Maniglio, M.A. Rodrìguez-Valverde, S. Siboni; Dept. Of Materials Engineering, University of Trento,
Via Mesiano 77,38050 Trento, ITALY
Recent Advances in the Determination of an Equilibrium Contact Angle on Rough/heterogeneous Surfaces
The correct estimate of equilibrium contact angle of liquids on rough and/or heterogeneous solid surfaces is of great importance in order to understand adhesion phenomena, surface energetics, hydrophobicity or hydrophilicity. The interest is not from a merely theoretical point of view, but also for many practical applications, like the detection of surface biocompatibility of materials for medical devices. Vibrationally Induced Equilibrium Contact Angle (VIECA), in both dynamical (Wilhelmy microbalance) and static (sessile drop) version, provides a powerful approach to the experimental measurement of equilibrium contact angle on moderately non-ideal surfaces. It is able to determine a well-reproducible estimate of the thermodynamical contact angle which, being systematically intermediate between advancing and receeding, typically stable and almost insensitive to environmental mechanical noise, seems much more satisfactory than the usual advancing or receeding values. The advantages of VIECA are illustrated on some model surfaces, supporting the idea that VIECA estimates is a good candidate to experimentally approximate Wenzel or Cassie-Baxter contact angle in rough and heterogeneous surfaces. An extrapolation of those values allows to obtain a candidate for the Young angle.
M. Brugnara, M.A. Rodríguez-Valverde, S. Siboni and C. Della Volpe;
Polymers and Composites Laboratory, Dept. of Materials Engineering and Industrial Technologies, University of Trento. E- 38050 Trento, ITALY
Comparison of Algebraic Algorithms for Drop Profile Fitting: Circle and Ellipse
Evidently, the understanding of wetting phenomena requires new theoretical approaches describing the wettability of non-ideal solid surfaces. However, some aspects in the goniometric techniques still appear nowadays unclear. In the sessile drop method, the choice of a suitable algebraic model for the drop profile fitting is not so simple. The validity of this model will depend on the contact angle and drop volume ranges.
The main advantage of fitting algebraic models is their mathematical simplicity and by contrast, the main disadvantage is the lacking of a precise physical meaning. These algorithms are not a solution of Young-Laplace equation including gravity effects; nevertheless, they easily allow to evaluate a geometrical quantity like the phenomenological contact angle. The statistical goodness of these models can compensate the absence of physical consistency.
Circle and ellipse models were tested on simulated and real sessile drops of practical volumes (<5microliters) and water capillary length. For greater volumes, a laplacian solution is required. The error propagation in the contact angle value was based on the random perturbation of drop profiles.
The results show that the circle fitting algorithm is more suitable if drops are moderately symmetric and the contact angle is low. Otherwise when the drops exhibit some asymmetry then an ellipse fitting algorithm represents a good alternative.
Anselm Kuhn, and John Durkee; 437 Mack Hollimon, Kerrville, TX 78028
Wettability Measurements for Surface Cleanliness Testing - an Old Technique Revisited & Updated
That wettability measurements can be used to characterize surface cleanliness has been known for over 70 years. Today, however, a huge dichotomy has developed. On the one hand, highly sophisticated, computer-controlled goniometers with video cameras and supporting software packages are available. On the other hand, industry continues to use (or misuse) the rudimentary and fallible "water break" test. This presentation will describe alternatives between these two extremes, including the Nordtest Poly 197 Standard, using dyne liquids with micro pipettes, and advances in goniometry. The availability of low-cost, high-resolution digital cameras, free computer software and moderately-priced electronic pipettes allows multiple sessile drop measurements to be made within a few minutes, using the Bikerman method, on large surface areas in an industrial setting.
Other developments in goniometry will also be noted: portable goniometers which can be used on any large and most curved surfaces, patented modifications thereto, and a comment on Langmuir's largely-forgotten reflecting goniometer and its subsequent developments. Some case studies will be presented showing the use of wettability measurements and surface energy values derived from them, in the surface finishing industry.
C. W. Extrand; Entegris Inc., 3500 Lyman Blvd., Chaska, MN 55318
Modeling Ultralyophobicity: a Liquid Drop Suspended on a Single Asperity
With an eye towards understanding the underlying physical phenomenon associated with utlralyophobic surfaces (or super repellent surfaces), model studies have been performed on single asperities of different size and shape. For example, smooth glass rods were coated with an amorphous fluoropolymer and mounted vertically. A small liquid drop was deposited on top of each rod and liquid was sequentially added. If the liquid had a relatively low contact angle, then as soon as the suspended drop established its advancing contact angle on the side of the rod, the drop collapsed and the liquid flowed down the side of the rod, as first described by Mason and colleagues (1). On the other hand, if the contact angle was sufficiently large, it was possible to suspend a much larger drop atop the model asperity with an apparent contact angle approaching 180░. If more and more liquid was added, eventually the large, suspended drop collapsed and cascaded down the rod. Using an analysis that accounts for both capillary forces and the influence of gravity, the critical volume to instigate collapse was correctly predicted for each liquid/asperity combination.
1. Oliver, J.F.; Huh, C.; Mason, S.G. J. Colloid & Interface Science 1977, 59, 568.
A. Méndez-Vilas1, M.G. Donoso1, J.L. González-Carrasco2, J.M. Bruque1, M.L. González-Martín1
1) Department of Physics, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
2) CENIM-CSIC, Avda Gregorio del Amo 8, Madrid 28040, SPAIN
AFM Micro-Topography and Contact Angle Goniometry on Ti-Based Biomaterials
Micro-topography is relevant among the surface properties of biomaterials because of the very different size, shape and flexibility of cells and microorganisms. Two of the main characteristics needed to be known to get a proper description of the surface topography are surface area and roughness -evaluated as Ra or RMS roughness-. Despite both characteristics are related, it is emphasised that they do not ever correlate when roughness is given in terms of RMS.
Surface topography of polished and blasted samples of a Ti6Al4V biomaterial has been studied using an Atomic Force Microscope. Surface RMS roughness and surface area have been measured at different scales. While at distances below 10 Ám the surface RMS roughness in both kinds of samples is not very different, this difference becomes significant at larger scanning sizes. This microscopic information is contrasted with that coming from macroscopic contact angles measured for different liquids. Interpretation of these results are in accordance with the microscopic analysis done through the use of a functional roughness parameter evaluated from AFM images, which has been shown not to correlate with the RMS roughness, the most commonly used roughness parameter.
M.L. González-Martín1, A.M. Gallardo-Moreno1, R. Calzado-Montero1, J.M. Bruque1, C. Pérez-Giraldo2
1) Department of Physics, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
2) Department of Microbiology, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
Physico-Chemisty of Initial Bacterial Adhesion. Insigts into the Relations Between Experiments and Model Proposals
There are not doubts that physico-chemical parameters of microorganisms and biomaterials are decisive in the initial bacterial colonization of host surfaces, with the subsequent development of infectious processes. However, there is not consensus about the degree of participation of hydrophobicity, surface tension or charge, which, in turn, is related to the fact that theoretical interpretations of bacterial adhesion, in terms of DLVO or XDLVO theories, do not always agree with "in vitro" adhesion results.
This work seeks to understand the role of physico-chemical surface properties of bacteria in in vitro adhesion tests. A parallel plate flow chamber is used and MATS method is performed using in both cases initial adhesion rates as indicators of initial bacterial colonization. Results are contrasted with physico-chemical parameters and the interaction free energy predicted by DLVO and XDLVO theories, getting inside the importance of the interaction distance.
O. Karoussi, A. A. Hamouda; University of Stavanger, P. O. Box 8002 Ullandhaug, 4068 NORWAY
The Effect of Binary Fatty Acids Systems on Partitioning, IFT and Wettability of Calcite Surfaces
It is our experience that the presence of fatty acids in oil reservoir alters the wettability of calcite surfaces. In our earlier work we have shown that fatty acids (long chain) alters the water wet calcite surface to oil wet in presence of water. An extensive study on the alteration mechanism is currently on going for individual fatty acid in our laboratories.
In this paper the work is extended to include the wettability alteration of calcite surface in binary fatty acid systems. The selected fatty acids are based on the distribution abundance of long chain fatty acids that exists in the North Sea oil reservoirs. The long chain fatty acids mostly reside in the oil phase, but partition into the water phase depends on the physicochemical properties of the system and conditions.
The presented work in this paper includes the effect of binary systems of saturated (stearic) unsaturated aliphatic (oleic) and naphthenic (18-phenoloctadecanoic) acids on the wettability for a comparison with single fatty acid systems. The work comprises use of different methods, such as partitioning, IFT and contact angles. The results are interpreted to obtain a global picture of the different factors that affect the ultimate change of the wettability of the calcite.
L. Labajos-Broncano, M. J. Nuevo, M. L. González-Martín, J. A Antequera-Barroso and J. M. Bruque; Department of Physics, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
An Experimental Study about the Effect of the Interfacial Adsorption on the Imbibition of Aqueous Surfactant Solutions in Hydrophilic Porous Media
Imbibition of aqueous solutions of surfactants in porous media is a topic of noteworthy interest that has given rise to a set of important research works where the physical bases of this phenomenon are investigated. All of them put into relief the importance of the interfacial adsorption in the dynamic of the process. On the one hand, the adsorption at the liquid-vapour interface decreases the surface tension of the solution with regard to the value of the solvent. On the other, the adsorption at the solid-liquid interface could modify the energetic features of the solid surface causing an alteration in the contact angle. Therefore, it is expected the velocity of the imbibition to depend on the surfactant concentration. However, this last adsorption could cause depletion in the number of surfactant molecules adsorbed at the liquid-vapour interface, which could be total depending on its strength. If it were so, the imbibition would not be affected by the surfactant concentration, it being identical to the corresponding to water. The contribution we would like to present is precisely related to this last hypothesis. So, some experimental results, proceeding from studies about imbibition in different hydrophilic porous media we have carried out, will be shown. In order to precise the influence of the solid-liquid adsorption on the imbibition, it has been employed surfactant that can be or not adsorbed on the solid surfaces, and in the first case, it has been also studied the effect of this adsorption if it is carried out on the solid surface before the imbibition.
Authors gratefully knowledge the financial support given by Junta de Extremadura - Consejería de Infraestructuras y
Desarrollo Tecnológico (Dirección General de Investigación, Desarrollo Tecnológico e Innovación) under project 3PR05C011.
Ri Li , Naser Ashgriz*, Sanjeev Chandra, John R. Andrews and Stephan Drappel; University of Toronto, Mechanical Engineering, 5 King's College Road, Toronto, Ontario M5S3G8, CANADA
Apparent Solidification Contact Angles of Micro-droplets of Hot Melt Ink Deposited on Solid Surfaces
An experimental investigation of apparent solidification contact angle formed in deposition of ink droplets on solid surfaces as occurs in offset ink-jet printers is presented. The apparent solidification contact angles of 39 mm droplets of hot melt ink impacting on sub-cooled solid surfaces under different printing conditions are obtained. The printing condition is varied by changing four parameters: the type of substrate, the distance between the substrate surface and printhead, the substrate temperature and the printhead jetting temperature. It is found that the apparent contact angle is not only dependent on the substrate material and substrate temperature but also has strong dependence on the impact velocity and temperature of the droplet. Explanation is provided by considering the coupling effect of viscous damping and impact process.
* To whom correspondence should be sent
Tao Du, Yazhen Wang, Peng Xia, Yan Luo; Research Center of Material Science and Engineering, Guilin University of Electronic Technology, Guilin, CHINA
Study of ABS Resin Bond with Acrylonitrile-Modified Epoxy Resin
A serial of amine hardeners modified with acrylonitrile were synthesized, the amine values at about 662mgKOH/g, and were used to bond ABS resin. When the nitrile grouping content of the cured epoxy resin increased from neat to 0.645mmol/g, the shrinkages of the epoxy resins cured with the synthesized amine hardeners kept unchanged, approximately 0.2%, the contact angels between the cured epoxy resin and ABS resins increased from 63 to 79 degree, and accordingly the adhesive strength between them increased from 11.8MPa to 18.6MPa. The results show that the incorporation of nitrile grouping improves the wettability and enhances the adhesive strength.
Thomas Luxbacher; Anton Paar GmbH, Anton-Paar-Strasse 20, A-8054 Graz, AUSTRIA
Comparison Between Water Contact Angle and the Electrokinetic Characterization of Solid Surfaces
The streaming potential method is presented as a complementary measuring technique to the determination of the water contact angle. The streaming potential measurement enables the determination of the zeta potential at the interface of macroscopic solid surfaces and a surrounding aqueous-based electrolyte solution, and furthermore i.a. the estimation of surface charge and the hydrophilic or hydrophobic character of these surfaces.
The empirical correlation between water contact angle data and streaming potential results is demonstrated with various case studies. For polymer surfaces the water contact angle shows a linear correlation with the maximum in zeta potential obtained from its dependence on the electrolyte concentration. For the characterization of sized glass fibres the streaming potential method shows higher sensitivity to changes in the surface chemistry than contact angle measurements. In the case of surface modification of polyolefines to introduce acidic functional surface groups, the plateau values of zeta potential observed in the alkaline pH range changes synchronously with the water contact angle.
Beside this agreement between streaming potential and contact angle results, the information gained by contact angle measurements may be extended with the streaming potential technique.
Glen McHale1, Michael I. Newton1, Neil J. Shirtcliffe1, F. Brian Pyatt1 and Stefan H. Doerr 2
1) School of Biomedical & Natural Sciences, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK
2) Department of Geography University of Wales Swansea Singleton Park Swansea SA2 8PP, UK
Self-organisation of Soil and Granular Surfaces
Soil is often considered as an ideal water absorbing material, but under some conditions, such as forest fires or oil spillages on loose sandy soil, it can become extremely water repellent. The inability of water to penetrate from the surface into the soil increases rain water run-off and soil erosion and hinders the re-establishment of vegetation. In this work we show that a water droplet on a granular material can initiate an active process of lifting, self-coating and selectively concentrating small solid grains as it loses volume through evaporation or partial infiltration into the substrate. From surface free energy considerations, we show that the sorting of these grains is a result of particles of different wettabilities competing for water-air interfacial surface area. As a result, reduction in droplet volume leads to the formation of temporary liquid marbles (droplets with particulate skins) and the eventual self-organisation of a mixed hydrophobic-hydrophilic aggregate into a hydrophobic shell surrounding a hydrophilic core. The features observed with hydrophobic soil apply to droplets of other liquids interacting with granular or powdery media and we therefore anticipate that self-coating and self-organisation driven by liquid volume changes and wettability will be important in many industrial processes.
The authors' acknowledges the financial support of the UK EPSRC and MOD/Dstl (EP/C509161/1).
Glen McHale, Michael I. Newton, Dale L. Herbertson, Neil J. Shirtcliffe and Stephen J. Elliott; School of Biomedical & Natural Sciences , Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK
Electrowetting on Super-hydrophobic Surfaces
A well-known effect of topographic enhancement of wettability is the roll-up of water droplets to create super-hydrophobicity. In contrast, spreading of a water droplet can be induced by electrical charging of the liquid-solid interface. Attempts to combine these two effects to obtain completely tunable wetting has been found to cause an irreversible transition from a highly mobile droplet to one that is immobilized due to the penetration of the water into the surface features. In this work, we report progress on electrowetting on photolithographically produced surfaces consisting of micro-scale posts and describe how the irreversible transition can be analyzed to provide an estimate of the surface roughness of the substrate, which is in agreement with the Wenzel equation. We then show that the irreversible nature of electrowetting on super-hydrophobic surfaces can be overcome by making the solid topographic surface structure part of the "skin" of the water droplet to create a liquid marble-on-solid system. In a liquid marble, hydrophobic grains attach to the water-air interface creating a conformable "skin" and electrowetting can be performed with the water remaining effectively suspended on the grains. The theoretical basis and experimental behavior of this reversible electrowetting system of mobile droplets will be described.
The authors' acknowledges the financial support of the UK EPSRC and MOD/Dstl (GR/S34168/01) and the assistance of Mr P.
R. N. Jagtap; Reader in Paint Technology, University of Mumbai, Institute of Chemical Technology, N.M.Parekh Marg, Matunga, Mumbai 400 019 INDIA
Stimulate of Contact Angle with Respect to Grafting of Butyl Acrylate Hybrid - Pud Adhesives for Plastic Laminates
Hybrid PUDs synthesized using varying divisions of butyl acrylate, from 0 (i.e. NMP as a cosolvent) to 50 wt. % for the adhesive applications, for plastics laminates, like PET and LDPE. Theses adhesives were characterized for particle size analysis and contact angle measurement, while grafting efficiency of butyl acrylate on PU, evaluated by FTIR and solvent extraction technique. Stimulate of different ratio of BA to PUDs hybrid on peel strength of flexible laminates, contact angle and efficiency of grafting of acrylic monomer on PU backbone were studied. It was observed that with increasing in butyl acrylate content in the hybrid-PUDs, the particle size and grafting efficiency decreased. These adhesives exhibited very good peel strength for the PET-LDPE laminates, whereas fair for PET-PET and poor for LDPE-LDPE laminates. A strong relation was established between the grafting lengths of the butyl acrylate on the adhesion characteristics of the hybrid PUD. At 40 wt% of butyl acrylate in hybrid - PUDs the graft length was the highest, while the contact angle and the peel strength for the plastics laminates were lowest. In short butyl acrylate -PUD interpenetrating network are better than butyl acrylate- PUD partly grafted adhesives for plastic laminates.
Mika M. Kohonen; Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, AUSTRALIA
The Effects of Wall Sculpturing, Sap Solutes, and Drying on the Wettability of Tree Capillaries
The wettability of the lumen walls of the water-conducting capillaries in plants (tracheids and vessels) is an important parameter in understanding the transport of water in living plants. Lumen wettability is also important in the processing and use of wood as a material. However, although the macroscopic wettability of wood surfaces has received considerable attention, very little is known at the microscopic scale. For example, it has only recently been realised that fresh xylem capillaries are not completely wetted by water, as commonly assumed by plant physiologists.
In this presentation I will describe measurements of the wettability of the lumen walls of tracheids of various species of Australian cypress (Callitris Vent.). Wettability was studied by analysing microscope images of bubbles produced in the tracheids upon rewetting of dehydrated sapwood samples. I show that wall roughness (the warty layer) significantly increases the wettability of the lumen wall, an observation which provides an appealing answer to the long-standing debate on the function of wall sculpturing in xylem conduits, and which may provide clues for the biomimetic engineering of the wettability of microfluidic channels. I will also describe the significant effects of soluble sap constituents and air-drying on lumen wettability. The results have important implications in both plant physiology and wood technology.
Juha Lindfors, Janne Laine and Per Stenius, Laboratory of Forest Products Chemistry, Helsinki University of Technology - TKK, FINLAND
Adhesion of Hydrophobing Agents to Wet and Dry Surfaces
The adhesion of some typical hydrophobing agents of the type used for paper and board - alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD) - on materials having different surface energetics was studied. Adhesion was measured through contact angle measurements and by means of a recently developed contact mechanical technique ("MAMA"1) based on JKR methodology. Generally, it was found that the more hydrophilic the surface, the higher the adhesion of the hydrophobing agents to surfaces in air. On solids immersed in water the trend was opposite to that in air and the differences between the values of adhesion to different surfaces were more distinct. The correlation between different methods to evaluate the work of adhesion will be discussed and the suitability of these methods for different applications will be reviewed. Recommendations for a specific case of adhesion - avoiding contamination on paper machines - are also given.
Chuan Guo Ma 1, 2, Min Zhi Rong1, Ming Qiu Zhang1
1) Materials Science Institute, Zhongshan University, Guangzhou 510275, P. R. CHINA
2) Department of Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, P. R. CHINA
Use of Wetting Coefficient plus Surface and Adhesive Work to Predict Dispersion State of Nano-CaCO3 Fillers
In this work, the morphology was studied in ternary composites of polypropylene with nano-CaCO3 fillers and elastomer inclusions. Firstly, surface characteristic of each component in composites, surface tension including its dispersion component and polar component was measured. Then wetting coefficient, interface surface and adhesive work were calculated to predict dispersion state of nano-CaCO3 fillers, respectively. The results showed that the predictions were well consistent with the facts observed by SEM, and that, predictions by wetting coefficient among three parameters were more advisable. Encapsulation of the filler by poly(butyl acrylate) elastomer was achieved using butyl acrylate-grafted nano-CaCO3. Separation of the filler and Polyolefin elastomer particles was achieved using untreated nano-CaCO3.
Ilker S. Bayer and Constantine M. Megaridis; Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607-7022
Daniel R. Gamota and Jie Zhang; Physical Realization Research Center, Motorola Labs, Schaumburg, IL 60196
Surface Free Energy Estimation and Wettability Characterization of UV Curable Coatings by Contact Angle Measurements
Surface energy determination of a solid is essential when considering surface properties in the areas of wetting/ adhesion, friction/lubrication, and surface modification. One common technique for determining the surface energy of a solid/air interface (S ) is contact angle measurement, which utilizes the angle () at the three-phase contact and the surface energy of a liquid/air interface (L) to estimate S . In many industrial sectors, polymer surfaces play an important role for the production of high-quality consumer goods. In this connection, the coating and painting of these materials is of particular importance. This study aims at estimating surface energy components of various UV-curable polymer surfaces, such as cycloaliphatic epoxide resins and acrylic resins, which are widely used in electronic coating industries. Thin films of these polymers were either spin coated or spray cast on smooth flexible aluminum substrates. Both solvent-based and solvent-less coatings were applied depending on the polymer viscosity. After adequate UV curing of the thin polymer films, the surface free energy parameters of the investigated surfaces were calculated using the contact angle data of various probe liquids. The results are analyzed according to: (a) Fowkes's geometric mean method , and (b) van Oss's acid-base method . Based on these measurements, various conclusions are made on the wetting and adhesion characteristics of these surfaces.
 F.M. Fowkes, J. Adhes. Sci. Technol. 1 (1987) 7.
 C.J. van Oss, R.J. Good, M.K. Chaudury, Langmuir 4 (1998) 884.
A. Méndez-Vilas, A.B. Jódar-Reyes, M.G. Donoso, J.M. Bruque and M.L. González-Martín; Department of Physics, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
Nanoscale Exploration of Wetting/Dewetting Phenomena at Silicon Wafer Surface
Nanoscale exploration of wetting/dewetting phenomena at a quite flat silicon wafer surface, showing nanometer-sized surface roughness, should give rise to a better analysis of the surface hydrophobicity at the nanoscale. This would help to a better understanding of the adsorption behavior of proteins and surfactants, whose sizes are usually in the nanoscale region. Molecularly Thin Liquid-like Films, water droplets and Fractal Structures, thought to be bounded water, have been observed using Non-Contact AFM. Phase imaging has been used to get insight into the physical nature of the different structures observed and nanodroplet profiles have been analyzed to calculate contact angles from nanoscopic techniques.
Masataka Murahara; Entropia Laser Initiative Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro, Tokyo, 152-8552, JAPAN
Electrowetting-induced Photochemical Surface Modification of PTFE by Using ArF Laser
The fluorocarbon (PTFE) was modified into hydrophilic with 1/100 of the shots number required to obtain the same contact angle with water by the laser irradiation alone, when irradiating an ArF excimer laser on the sample surface at the moment of applying a 6 kV to the water placed on the PTFE surface to decrease the contact angle with water.
A high voltage (6 kV) of direct current (DC) or alternating current (AC) was applied on the gap, and the ArF excimer laser was vertically irradiated on the sample surface. The water was photo-dissociated to produce H and OH. At the same time, the C-F bond of the PTFE was also photo-dissociated, and the F atom bonded to the H atom to produce HF. The OH group united with the dangling bond of C, which resulted in modifying the PTFE surface to be hydrophilic. By combined high voltage application and ArF excimer laser irradiation treatments, however, the 50-degree contact angle was yielded with 500 shots, 1/20 of 10000, when applying the DC of 6 kV, and with 100 shots only, 1/100 of 10000, when applying the AC of 6 kV. Moreover, the modified sample was observed for a change in contact angle with passage of time. The contact angle was 60 degrees after applying the high voltage, and 110 degrees when stopped. On the other hand, the sample modified by combined the high voltage application and ArF excimer laser irradiation maintained the 50-degree contact angle for one month after stopping the voltage application.
M. J. Nuevo, L. Labajos-Broncano, M. L. González-Martín and J. M. Bruque; Department of Physics, University of Extremadura, Campus Universitario, Avda. de Elvas s/n, 06071, Badajoz, SPAIN
An Experimental Study about the Effect of the Velocity on the Contact Angle in Experiments of Spontaneous Flow of Liquids in Porous Media
One of the main problems that comes when analysing the results of imbibition experiments in porous media is related to the determination of the possible effect of the velocity of the process on the contact angle. Usually, the study of the experimental results is carried out through Washburn's equation, which assumes the contact angle is a constant quantity taking a similar value to that one corresponding to equilibrium conditions. However, some research works have shown that the contact angle is a quantity that could show a dynamic behaviour of the imbibition. If it were so, this equation should be modified to take it into consideration. These works establish the contact angle as a function of the capillary number, which take into account the magnitude of the interfacial force against the viscous forces. Some theories and empirical equations have been proposed in order to describe the observed behaviour. Nevertheless, it has to be pointed out that the experiments where the dependence of the contact angle with the velocity has been found consisted of forced rise of liquids in capillaries, or induced movements of drops on flat solid surfaces. Whether spontaneous flow of liquids in porous media is affected by this effect continues being unknown. One could wonder how the cause of the movement -the contact angle- could be altered by its proper consequence -the imbibition velocity. The work we present here pretends to throw some light about the subject raised before. Concretely, it will be shown imbibition experiments carried out with diverse porous solids and liquids where the capillary number takes different values. Through this experimental study, it is sought to analyse if some of the proposed physics models predicts or describes the observed behaviour. Besides, they will be compared with the classical description given by Washburn's equation. With this purpose, a new analysis procedure, consisting of the direct study of the velocity associated to the imbibition, will be employed.
Authors gratefully knowledge the financial support given by Junta de Extremadura - Consejería de Infraestructuras y
Desarrollo Tecnológico (Dirección General de Investigación, Desarrollo Tecnológico e Innovación) under project 3PR05C011.
Klaus Opwis, Thomas Bahners and Eckhard Schollmeyer; Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY
Surface Modifications for the Control of Cell Growth on Textile Substrates
Wanted or un-wanted cell growth on fiber surfaces is an important aspect of many high-performance textiles made of synthetic fibers. The biocompatibility of textile implants, the need to prevent clogging in artificial blood vessels or in textile used for blood filtration or even anti-fouling properties of outdoor technical textiles are examples in that context. In all cases the adsorption of proteins forms the initial step of cell growth. Accordingly, the aim of a controlled modification of surface properties may be to enhance or prohibit protein adsorption. Different approaches based on a photochemical modification of the surface chemistry of fibers made PET were studied with respect to the proteins albumin and fibrinogen.
The potential of the irradiation of the synthetic fiber in the presence of a reactive substance to establish functional groups is well-known. The use of bi-functional substances offers further possibilities, e.g. cross-linking of thin-layers but also bonding of additional molecules.
The first part of this work concentrates on the direct immobilization of proteins on the fiber surface in order to enhance cell growth. Here, the fibers were irradiated in the presence of substances like diallylphthalate (DAP) and the protein. The DAP is meant to form a network incorporating the protein. Further work concentrated on the prevention of cell-growth making use of the well-known property of low molecular weight polyethyleneglykol (PEG) to decrease unspecific protein adsorption. PEG is easily cross-linked on the PET fiber surface using the described photo-chemical process.
Thierry Ondarçuhu1, Agnès Piednoir2
1) Nanoscience group, CEMES-CNRS, 29 rue Jeanne Marvig, 31055 Toulouse, FRANCE
2) Université de la Méditerranée, Campus de Luminy, Case 901, 13288 Marseille FRANCE
Interaction of a Contact Line With Nanometric Steps
The laws governing the spreading of liquids on surfaces are well understood at the macroscopic scale but little is known when scaling down to nanometer scale. In particular, the structure of the liquid in the very close vicinity of the contact line remains largely unknown. We used steps on alumina and graphite surfaces to probe, at nanometer scale, the structure of the contact line. The interaction of the contact line with the steps is observed during the dewetting of polystyrene films on these surfaces. We observe that, for steps heights larger than a critical value, the hole is asymmetric: the contact line is blocked by downwards steps whereas it passes through upwards steps with no interaction. This behavior is explained by simple macroscopic considerations based on the equilibrium contact angle. For steps smaller than this critical value, the contact line is insensitive to the steps: the hole grows symmetrically as on a homogeneous surface. Statistics with various polystyrene over a large number of steps on alumina show that the critical step height is about 3 times the radius of gyration of the polymer. This shows that the "macroscopic" description remains valid down to dimensions of the order of the diameter of one single molecular chain.
Pinning of a contact line on nanometric steps during the dewetting of a terraced substrate, T. Ondarçuhu, A. Piednoir NanoLett 5 (2005) 1744-1750.
Acknowledgement : We thank E. Dujardin and E. Raphaël of fruitful discussions. The partial support of the EC-funded project NaPa (Contract no.NMP4-CT-2003-500120) is gratefully acknowledged.
Statistics on the anchoring condition of a contact line on nanometric steps as a function of the polymer radius of gyration with AFM images of the two distinct situations.
Aiping Fang,1 Thierry Ondarçuhu,1 Erik Dujardin,1 André Meister,2 Raphaël Pugin2
1) Centre d'Elaboration des Matériaux et d'Etudes Structurales, CEMES-CNRS, 29 rue Jeanne Marvig, 31055 Toulouse cedex 4, FRANCE
2) Swiss Center for Electronics and Microtechnology (CSEM), CH-2007 Neuchâtel, SWITZERLAND
Nanoscale Dispensing of Droplets
We report on a newly developed liquid nanodispensing system (NADIS) designed to pattern substrates on the nanometer scale by deposition of nanodroplets. This AFM-based method uses a small aperture milled by Focused Ion Beam (FIB) at the apex of a hollow AFM tip to transfer liquid from a reservoir to the surface. We discuss the influence of the various parameters (hole size, tip functionalizationů) on the size of the deposited droplets. The dynamics of the process is also deduced from force curve measurements during the deposition. We show that attoliter droplets (100 nm in diameter) can be reproducibly dispensed on a surface opening the way to single molecule deposition.
- Meister, A.; Liley, M.; Brugger, J.; Pugin, R.; Heinzelmann, H. Appl. Phys. Lett. 2004, 85, 6260-6262.
- Fang A., Ondarçuhu T., Dujardin E, Meister A., Pugin R., Nanolett. submitted.
Acknowledgement : The partial support of the EC-funded project NaPa (Contract no.NMP4-CT-2003-500120) is gratefully acknowledged.
Array of nanodroplets (diameter 250 nm) deposited by NADIS on an amine treated silica surface.
Dennis Palms1,3, Rick Fabretto1, Rossen Sedev1, Joel De Coninck2 and John Ralston1
1) Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095
2) Centre de Recherche en Modelisation Moleculaire, Universite de Mons Hainaut, 7000 Mons, BELGIUM
Measurement and Interpretation of Dynamic Contact Angles and Contact Angle Hysteresis
The contact angle (CA) that a liquid forms on a solid surface is the principal analytical parameter to elucidate the wetting properties of the given system. For any real surface though, there is no single contact angle, but various angles exist and usually differ from each other. This work aims at elucidating the roles these different angles play and how they can be interpreted to obtain a wider picture of the solid-liquid interactions, which are of great importance for applications like coating, printing, selective deposition, or biosensors.
Dynamic contact angles (DCA) of water and squalane on two surfaces, poly ethylene terephthalate (PET) and an amorphous fluoropolymer (AF1600), were determined over a velocity range of four orders of magnitude using the Wilhelmy Plate Technique. The molecular kinetic theory of wetting (MKT) was applied to analyse the data and calculate (static) advancing and receding contact angles rather than waiting an appropriate amount of time after forced movement of the three-phase contact line. Special care was given to the data fitting to reliably extract the principal parameters of the MKT, the average distance between two adsorption sites, âÜ, and the quasi-equilibrium jump frequency, K0.
Mechanical energy was introduced to the system to obtain a ížvibratedíĘ angle, where acoustic vibrations were applied at specific time intervals. Analysis of the data indicated that the same single-valued contact angle was obtained regardless of whether the contact line was advancing or receding over the substrate, allowing a good estimate for the equilibrium contact angle.
Jin-Goo Park; Hanyang University, Div. of Materials and Chemical Engineering, Ansan, 426-791, KOREA
Preparation and Characterization of Hydrophobic Anti-stiction Layer in Nano Imprinting
(Abstract not yet available)
M. Ojha, S. Panchangam. P.C. Wayner, Jr. and J. L. Plawsky; Dept of Chemical and Biological Engineering, Rensselaer Polytechnic Institute
110 Eighth St., Troy, NY 12180
Effects of Surface Structure on Contact Line Behavior
The effects of surface structure on the contact angle and wettability of surfaces has a long history dating back more than 50 years to the pioneering work of Cassie, Wenzel, Goode and others. Recently, the effects of surface roughness has become important as work on superhydrophobic surfaces by Miwa et al. and patterned, switchable surfaces by Lahann et al. has generated a great deall of interest. The atomic force microscope has enabled detailed characterization of surface roughness and enabled researchers to tie roughness to the macroscopic contact angle, however little work has been done at the microscale, trying to tie surface parameters to properties of a meniscus at the contact line. Here we report on studies looking at octane and pentane on structured surfaces formed by plasma etching and deposition processes and by the deposition of a thin, nanoporous film. We note that the adsorbed film thickness ahead of the contact line is a strong function of surface roughness as is the contact angle and curvature at the contact line. Both the contact angle and curvature exhibit large jumps in the region of the contact line that are functions of the surface roughness. The variation in adsorbed film thickness leads to an apparent Hamaker constant that is now a function of the surface structure as well as the dielectric properties of the media.
Carel Jan van Oss; Department of Microbiology and Immunology; Department of Chemical and Biological Engineering, and Department of Geology; University at Buffalo, State University of New York, South Campus, Buffalo, NY 14214-3000
Properties of Water in Colloidal And Biological Systems
Some of the different unusual and hitherto often unstudied physico-chemical properties of water which, in various ways, are at the origin of the polar interactions occurring in water, are discussed. These properties include the hyper-hydrophobicity of the water-air interface, the cluster formation of water molecules in the liquid state and the extraordinary variability of the ratio of the electron-accepticity to the electron-donicity of liquid water as a function of temperature (T). This ratio is linked to the cluster size of liquid water and is in contrast with the product of the electron-accepticity and the electron-donicity of liquid water (i.e., the quantitative expression of its polar cohesion energy) which varies very little with T. These phenomena, which are typical for liquid water, influence all polar interactions that take place in it. All of these are treated from the viewpoint of the properties of liquid water itself, including the properties of advancing ice fronts when immersed in water and the surface properties of ice at 0o C.
Frieder Mugele; University of Twente, PO Box 217, 7500 AE Enschede, THE NETHERLANDS
Generation of Charge-Controlled Microdroplets Using AC-Electrowetting
Electric fields are a versatile tool both for the manipulation and for the generation of liquid droplets in microfluidic applications.
Here, we present an experiment that combines both aspects. Liquid droplets in a standard electrowetting configuration are
induced to oscillate periodically between two morphologies, one in which the droplet is attached to a wire that is barely
immersed into the droplet at zero voltage, and a second one in which the droplet is detached from the wire. As the droplet
oscillates between the two morphologies, it forms a thin capillary neck that eventually pinches off in each oscillation cycle. The
charge of the droplet immediately after the detachment is determined is determined by the relation between the frequency of
the applied AC voltage and the RC time constant of the droplet which diverges as the diameter of the capillary neck vanishes.
For high frequency (or low liquid conductivity) the droplet is discharged during the pinch off process resulting in an abrupt
increase of the contact angle. Under these conditions, the droplet oscillation dynamics are entirely determined by the
hydrodynamic response of the system to the abrupt contact angle variation upon breaking or re-establishing the connection to
the wire. This is evidenced by the good agreement between the experimental surface profiles and corresponding computational
fluid dynamics calculations using the volume of fluid method. As an application we demonstrate that self-excited droplet
oscillations can be used to promote mixing in digital microfluidic devices. Finally, we emphasize that the discharging
mechanism presented here is applicable to any situations involving electric field-induced droplet generation, such as
continuous inkjet printing or electrospray ionization.
Hossein Tavana and A. Wilhelm Neumann; Department of Mechanical Eng., University of Toronto, Toronto, Ontario M5S IA4, CANADA
Contact Angles: Measurement and Interpretation
Contact angles measured with many liquids on a given polymeric solid surface fall close to a smooth curve that represents the surface tension of the solid, when plotted as a function of liquid surface tension (lvcos vs. lv). However, the small deviations in the contact angles from these curves hinder the determination of solid surface tensions accurately. The deviations were disregarded in the past, since a suitable averaging yielded acceptable solid surface tensions with an error of 1-2 (mJ/m2). With the recent advancement in the measurement techniques, it was shown that the deviations are not experimental errors but have physical causes. Investigation of contact angles of a series of n-alkanes and liquids consisting of "bulky" molecules on the films of different fluoropolymers identified several mechanisms as the possible cause for the deviations: vapor adsorption onto the polymer film, alignment of liquid molecules in the vicinity of the solid surface, reorientation of the polymer chains upon contact with the test liquids, and strong dipolar interactions between liquid molecules and polymer chains. It is shown that shape, size, chemical composition, and the molecular configuration of liquid molecules as well as of the polymer chains all play a role. In the light of the results obtained, requirements for the determination of accurate surface tension of fluoropolymer films especially with respect to the probe liquids will be presented.
Dandina N. Rao and Subhash C. Ayirala; The Craft & Hawkins Department of Petroleum Engineering, Louisiana State University, Baton Rouge, LA 70803-6417
Mechanistic Modeling of Dynamic Vapor-Liquid Interfacial Tension in Complex Petroleum Fluids
Determination of vapor-liquid interfacial tension for crude oils is crucial in improved oil recovery processes such as gas and chemical injection, and in multiphase flow dynamics in porous media. The measurement of interfacial tension for complex fluids such as crude oils, especially at demanding conditions of pressure and temperature that exist in petroleum reservoirs, is arduous and hence there has long been a need for a simple model to predict interfacial tension in multicomponent hydrocarbon systems. In this paper, we propose a mechanistic model of dynamic vapor-liquid interfacial tension for crude oils based on individual phase compositions. The widely used parachor model has been modified to incorporate mass transfer effects through the ratio of vapor-liquid diffusivities raised to an exponent. The sign and magnitude of the exponent in the proposed model have been used to characterize the type and extent of the governing mass transfer mechanism (vaporizing or condensing) responsible for attaining vapor-liquid phase equilibria.
A detailed discussion on the 'parachor' concept has been provided to understand the underlying physics and thermodynamics. Three different crude oils with measured vapor-liquid interfacial tension data have been investigated using the proposed model. The proposed model has been able to predict vapor-liquid interfacial tensions accurately for all the three crude oils considered. Positive exponents obtained during modeling indicate that vaporization of components from crude oil into the vapor phase is the governing mass transfer mechanism for attaining vapor-liquid phase equilibria in these three cases. The exponent in the proposed model has been found to be a strong function of crude oil composition. In addition, this paper addresses the inadequacy of the currently available interfacial tension models to be applied to multicomponent hydrocarbon systems and thus provides a new mechanistic model to predict dynamic vapor-liquid interfacial tension in crude oils.
Mathilde Reyssat and David Quéré; ESPCI, Laboratoire de Physique et Mécanique des Milieux Hétérogènes, CNRS UMR 7636, Paris, FRANCE
On ź fakir ╗ Drops
Hydrophobic surfaces can be made super-hydrophobic by creating a texture on them. This effect, sometimes referred to as the "fakir effect", is due to air trapping in the structure, which provides a composite surface made of solid and air on which the deposited drop sits. Here we give evidence for this effect using forests of micro-pillars, made by photolithography and deep etching. This allows us to control the density of solid and air under the drop, and thus the degree of super-hydrophobicity. However, the "fakir state" is not always the most stable situation for a drop on a hydrophobic surface. The drop may instead fill the microstructure and this other state, called the "Wenzel state", has very different properties. We show how to observe transitions between these two states. We also achieve materials with a density gradient of micropillars, and discuss the possibility of inducing spontaneous drop motion on such surfaces.
SEM image of a surface decorated with a forest of micropillars.
Hans Riegler; MPIKG, Am Mühlenberg, D-14476 Potsdam, GERMANY
Wetting Properties, Interfacial Mobility and Aggregation Behaviour of Long Chain Alkanes at Solid/vapour Interfaces
(Abstract not yet available)
Université de Technologie de Compiègne, 60205 Compiègne Cedex, FRANCE
Influence of Wetting Parameters and Mixing Conditions on Characteristics of Water-rich Powders Obtained by Encapsulation
In a recent work the authors put across the development of water-rich powders containing up to 97 % (by weight) of water. Despite its high liquid content the product behaves still like a powder and can be characterized by its particle size distribution, apparent density and flow properties. The principle of the operation consists of mixing for 10 to 30 s the required amounts of the water and a highly hydrophobic powder in a high shear blender (17000 rpm). The hydrophobic powders are commercially available fumed silica constituted of sintered nanosize particles of silicon dioxide treated with various hydrophobic agents. In previous woks the authors pointed out the structure of fumed silica shells formed at the air/water interface using several techniques such as Langmuir-Blodgett balance, ESEM and freeze-fracture microscopy.
This work emphasizes the effects of mixing conditions (i.e. rotational speed and operating time) as well as the hydrophobicity extent of the fumed silica on the end-use properties (particle size distribution, form, density, flowability and minimum release pressure) of final products.
D. K. Sarkar, M. Farzaneh; Université du Québec à Chicoutimi, CANADA G7H 2B1
Superhydrophobic Aluminum Surfaces
Chemical etching has been used to create nanostructured patterns on aluminum surfaces. Micro/Nanostructures of the surfaces have been examined using Atomic Force Microscopy (AFM) and Scanning electron microscope (SEM). The patterned surfaces have been passivated using stearic acid and fluoroalkylsilane molecules to obtain low surface energy surfaces terminated with -CH3 and -CF3 radicals respectively. Optimized annealing temperatures have been obtained for both the systems to achieve highest contact angle and lowest hysteresis. These surfaces are found to be highly superhydrophobic with water contact angle more than 170o and have a very low hysteresis. However, -CF3 terminated surfaces show less hysteresis as compared to -CH3 terminated surfaces. These experimental results will be discussed in the lights of existing theoretical models.
N. Saleema1, D. K. Sarkar1, M. Farzaneh1, E. Sacher2
1) Canada Research Chair on Atmospheric Icing Engineering of Power Networks and Industrial Chair on Atmospheric Icing of Power Network Equipment, Université du Québec à Chicoutimi, CANADA G7H 2B1
2) Regroupement Québécois de Matériaux de Pointe, Department of Engineering Physics, École Polytechnique, C.P. 6079, Montreal, Québec., CANADA H3C 3A7
Effect of Temperature on Superhydrophobic Zinc Oxide Nanotowers
Superhydrophobic zinc oxide nanotowers have been grown successfully on silicon surfaces by chemical bath deposition (CBD).
Chemically and ultrasonically cleaned silicon substrates were immersed in a beaker containing 100 ml of 0.1M Zn(NO3) 6H2O
and 4 ml of NH4(OH) 28% solution. The CBD was performed in an oven at 70 oC for 20 minutes. The dried samples were
passivated using stearic acid (SA) molecules for lowering the surface energy. The SA passivated samples were annealed at
various temperatures ranging from 70 oC to 350 oC. Water contact angle measurements and Fourier transform infrared
spectrometry (FTIR) were performed for the samples at each annealed temperature. The achieved contact angle of water at
various temperatures remains nearly constant at 160o with a hysteresis of less than 5o and the tendency of water drop is to roll
off easily from the surface. FTIR studies reveal that the intensity of SA starts to reduce from 160 oC and evaporates completely
at 350oC making the sample highly hydrophilic. The partial passivation of surface due to annealing and the consequent
behavior of water contact angle will be discussed with the existing theoretical models considering the surface morphology of
ZnO nanostructured surfaces.
A. Safaee, D. K. Sarkar, M. Farzaneh; Université du Québec à Chicoutimi, CANADA G7H 2B1
Superhydrophobic Properties of Silver Coated Copper
Superhydrophobic properties of copper surfaces covered with silver nanoparticles have been studied. The silver nanoparticles
have been achieved by reduction of silver ions from silver nitrate solution on copper substrates using galvanic exchange
reaction. The sizes of the nanoparticles have been controlled by varying the concentration of the solution and the deposition
time. The concentration of silver ions was varied from 0 to 0.4 molar and the deposition time was varied from 1 to 1000
minutes. These nanostructured samples have been passivated with stearic acid molecules to obtain low surface-energy. The
contact angle and hysteresis of micrometer size water drops have been studied on these samples. The obtained contact angle
is as high as 150o and hysteresis is as low as 4o. However, strong dependence of hysteresis has been observed for the samples
obtained with different silver ion concentration in the solution. The experimental results, taking into account the surface
morphology, will be discussed with the existing theoretical models.
Frank Schröter1, Thomas Sottmann2, Dierk Knittel1, Eckhard Schollmeyer1
1) Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY
2) University of Cologne, Institute for Physical Chemistry, Luxemburger Str. 116 ,50939 Köln, GERMANY
Phase Behavior of Non-ionic Microemulsions of Water/Silicone Oil/Surfactant
Liquid mixtures of water, oil and amphiphiles are of growing interest in research and engineering. The behavior of these
systems is dependent on the chemical structure of the components and on pressure and temperature. Those systems show
one -, two- and threephase regions. With regard to certain application problems in the textile industry, the ternary phase
behavior of ethylene oxide surfactants with water and low molecular weight silicone oils, tetra- and pentacyclosiloxane (D4 and
D5), has been investigated. The objective of the studies was to define microemulsions, i.e. stable colloidal dispersions, with a
minimum amount of amphiphiles. Several systems were characterized with the help of concentration-temperature-diagrams
(fish-cut-diagrams). Furthermore, it was examined, if ethylene oxides are as effective as silicone polyether surfactants.
A. Synytska1, L. Ionov1,2, S. Minko3, K.-J. Eichhorn, M. Stamm1, K. Grundke1
1) Leibniz Institute of Polymer Research Dresden e.V., Hohe Str. 6, 01069 Dresden, GERMANY
2) Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307 Dresden, GERMANY
3) Clarkson University, Chemistry Department, Potsdam, NY13699-5810, USA
Model Structured Surfaces from Core-shell Particles. Influence of Chemical and Topographical Heterogeneities on Surface Wettability
It is well known that the surface properties of polymers are strongly influenced by the topography of the surface. In particular, wetting processes can be controlled by the surface roughness1-5. The understanding of wetting on rough surfaces is therefore of great importance for fundamental research, but also for numerous industrial applications such as coatings, paintings, adhesives, microfluidic technology, microelectronics, etc.
In this work we report about the preparation, characterization and application of regularly patterned surfaces for wetting experiments aimed to a better understanding of wetting on hydrophobic rough surfaces. This approach is based on use of core-shell colloidal particles. The surface is built up from self-assembled submicrometer- and micrometer-sized monodisperse core-shell particles forming ordered arrays6. Such surfaces can potentially be both model surfaces for fundamental research and templates for technologically relevant micro scale structures with unique geometric and topographic properties.
1. Barthlott W, Neinhuis C (1997) Planta 202: 1
2. Wenzel RN (1936) Ind Eng Chem Res 28: 988
3. Quere D (2003) Nanotechnology, 14: 1109
4. Patankar NA (2004) Langmuir 20: 7097
5. Marmur A, Krasovitski B (2003) Langmuir 19: 8343
6. Synytska, A.; Ionov, L., V. Dutschk, Eichhorn, K. - J., Minko, S., Stamm, M., Grundke, K. (2006) Progress in Colloid and
Polymer Science, in print.
H. Tavana, A. Amirfazli, and A.W. Neumann; Laboratory of Applied Surface Thermodynamics, Department of Mechanical and Industrial Engineering, University of Toronto, Toronto Ontario, CANADA
Fabrication of Superhydrophobic Surfaces of n-Hexatriacontane and Study of their Wetting Properties
Superhydrophobic surfaces can be fabricated by different techniques such as plasma etching, laser treating, sol-gel processing,
etc. These techniques are normally time-consuming and involve complicated multi-stage processes and application of several
treatments to attain desirable roughness and hydrophobicity. In this work, a straight-forward method is presented to prepare
superhydrophobic surfaces of n-hexatriacontane in a single-step process using a physical vapor adsorption (PVD) technique.
The randomly-distributed roughness features that vary in size from hundreds of nanometers to several micrometers combined
with the hydrophobic nature of n-hexatriacontane guarantees very large contact angles of ~171░ for water. Furthermore, very
small roll-off angle and contact angle hysteresis are obtained, indicating a Cassie wetting regime. Superhydrophobic surfaces
of n-hexatriacontane retain their wetting characteristics over a long period of time and are chemically stable, as confirmed by
contact angle measurements and XPS analysis, respectively.
S. Temmel1, T. Höfler2, W. Kern2
1) Polymer Competence Center Leoben GmbH, A-8700 Leoben, Austria
2) Graz University of Technology, Institute for Chemistry and Technology of Organic Materials, A-8010 Graz, Austria
Surface Properties of Polymers Functionalized by Uv Irradiation
In this paper we report on the surface properties of polymers obtained by UV-induced modification. The exposure of a polymer to UV light in the presence of an UV sensitive gas is a simple and effective way to increase the surface tension of a plastic to make it useful to various industrial applications. The introduction of acid groups (-SO3H) onto the surface of polyethylene was performed by photosulfonation. On the other hand ammonia in the presence of a VUV light source (Xe-excimer lamp) provides the attachment of basic groups (-NH2) onto LDPE or PVF surfaces. In both cases an increase in wettability and changes in electrochemical effects could be observed.
Moreover, we investigated the surface properties of polymers which contain photolabile groups. Photo-Fries rearrangements in
polymers containing phenyl ester units produce o-hydroxyphenone units. Both contact angle testing and zeta potential
measurements proved that acidic phenolic units are generated at the polymer surface upon UV illumination. The changes in (I)
surface tension, (II) streaming potential and (III) refractive index were investigated for several polymers containing phenyl
ester units. Such photoreactive layers are under investigation as functional surface coatings for a variety of substrates.
Po-zen Wong; Department of Physics, University of Massachusetts, Amherst, MA 01002
Multilayer Adsorption on Fractal Surfaces
When a liquid film is adsorbed on a fractal surface of dimension D, the film volume is expected to increase as V ~ l3D, where l
is a characteristic length scale given by either the film thickness t or the minimum radius of curvature r. It has been a common
practice to determine D by adsorption isotherm measurements in which t or r is varied by changing the vapor pressure P.
Some interpreted the data using the Frankel-Halsey-Hill equation for the film thickness t ~ [ln(P/Po)]1/3, but others have used
the Kelvin equation for the radius of curvature r ~ [ln(P/Po)]1. These two approaches are clearly in direct contradiction of each
other. We studied the problem by performing both small-angle scattering (SANS) and nitrogen adsorption isotherm
measurements on a common set of shale samples. The SANS results gave the fractal dimension D of each sample which was
then used to test the two interpretation schemes for the isotherms. We found that the FHH equation gave D < 2 for each
sample whereas the Kelvin equation consistently gave D values that were lower than the SANS results. In order to understand
this discrepancy, we carried out a numerical simulation of Van der Waals adsorption in a spherical pore. A power-law
distribution of such pores was used to represent a surface of known fractal dimension. The results show that film thickness and
curvature are both important at any vapor pressure and their effects could not be cleanly separated. Hence the use of either
the FHH equation or the Kelvin equation alone is an oversimplification of the situation and would generally lead to erroneous D
Mariëlle Wouters; TNO Industrial Technology, Polymer Technology, De Rondom 1, Eindhoven 5612 AP, THE NETHERLANDS
Aspects of Wettability and the Improvement of Adhesion of UV Curable Powdercoatings on Polypropylene Substrates
(Abstract not yet available)
Jerry Y. Y. Heng and Daryl R. Williams; Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
The Influence of Surface Chemistry in the Wetting Behaviour of Crystalline Pharmaceutical Solids
The surface energy of crystalline pharmaceutical solid state materials will influence its wetting, crystal growth, fracture, dispersion, colloidal stability, flow and adhesion properties. Thus, a comprehensive understanding of the wetting properties of pharmaceutical solids is of both a fundamental and practical importance in pharmaceutical product and process engineering.
In the work reported here, the wetting behaviour of two polymorphs (form I and form II) of paracetamol and racemates of ibuprofen were systematically investigated. This study was faciltated by the growth of macroscopic single crystals (> 2cm), enabling direct contact angle measurements on specific facets of the crystal. The advancing contact angles, a on various facets of these crystals were determimed using a liquid sessile drop, and the surface energy for the individual facets were computed using various semi-empirical relationships.
It was observed that the a of probe liquids is significantly different on various facets for both paracetamol polymorphs as well as for ibuprofen forms. In the polymorphic paracetamol system, where identical molecules assume different crystal lattices, both materials exhibited anisotropic wetting behaviour. Contrasting wetting phenomena was observed between the two forms of paracetamol and no relationship was found between similarly Miller indexed facets. The wetting behaviour for form I of paracetamol was however observed to depend on availabilities of hydroxyl groups on the surface of specific facets, as confirmed by X-ray Photoelectron Spectroscopy measurements. The wetting behaviour of racemic ibuprofen and S-(+)-ibuprofen were also anisotropic, but their differences were smaller owing to their similar crystal lattice dimensions.
Two alternate and somewhat opposing surface energy concepts have evolved during the past 40 years. A surface component
approach pioneered by Fowkes, but enhanced by Owens, Wendt, van Oss, Chaudhary, Good, and an equation of state model
proposed by Neumann. The wetting behaviour and the calculated surface energies for the crystalline solid systems reported
here reveals a direct correlation with the localised surface chemistry and structural morphology. The results of this work
supports the Fowkes' type of surface energy component approach.
Wen Zhong1, Ning Pan2, David Lukas3
1) Department of Textile Sciences, University of Manitoba, Winnipeg, MB R3T 2N2 CANADA
2) Department of Biological and Agricultural Engineering,
University of California, Davis, CA 95616
2) Technical University of Liberec, Liberec, CZECH REPUBLIC
Wetting and Adhesion in Fibrous Materials: Stochastic Modeling and Simulation
Wetting and adhesion are frequently observed phenomena in the processing and use of fibrous materials, when an interface is
created between fibrous substrate and a liquid or solid (i.e. coating or resin). Fibrous materials have a unique structure of
complex geometry, with pore distribution from intra-fiber to inter fiber spaces. Still, the physical basis of wetting and adhesion
are those molecular interactions within a solid or liquid or across the interface between a liquid and a solid. Stochastic
modeling and simulation methods, namely, Ising's model combined with Monte Carlo simulation, are therefore used in the
studies of wetting and adhesion behaviors of fibrous materials, including liquid wetting/wicking in fibrous structures, aerosol
deposition and filtration through fibrous filters, single fiber pull out process in a composite, and tearing behavior of coated
fabrics. The complicated mechanisms involved in different problems can be realistically simulated with a relatively simple
algorithm. The interaction across the interface (cohesion within a single substrate, adhesion between different media) can be
represented in a Hamiltonian expression of the system. The minimization of the system Hamiltonians yields the most likely
new steps for system evolvement, while the Monte Carlo method is used to select the one to actually occur, reflecting the
stochastic agreement with the behavior of real systems. The approach is proved to be useful in studies of similar interfacial