Meenakshi Annamalai and Thirumalai Venkatesan*; Nanoscience and Nanotechnology Institute (NUSNNI) – Nanocore, 5A Engineering Drive 1, T-Lab Building, National University of Singapore, Singapore 117411

Wetting Studies at Macro and Nanoscale

Understanding interaction of water molecules with the surface of different materials has become a very interesting theme of research. Large body of theoretical and experimental research work helps us to understand how the interfacial water exactly interacts with the surface structure/chemistry of the materials. Surface chemistry and surface roughness are the key properties that decide the interactions between water molecules and surfaces. Motivated in this direction, we have performed a systematic study of water contact angle and surface energy measurements on less explored oxide thin-films and two dimensional van der Waals structures ranging from exotic rare-earth oxides to graphene, MoS₂, WS₂ and their heterostructures. Alongside these macroscale measurements we also show an atomic scale approach to locally probe the wetting properties of materials. Such an approach enables to locally probe contact angles and evaluate surface energies of nanopatterned surfaces. In such a scenario using the conventional water droplet method would result in obtaining a value which is an average of all local values. Atomic scale measurements are also backed up by DFT calculations suggesting that molecular simulations and measurements on atomic scale can be extrapolated to macroscopic surface wetting problems.

^*Corresponding Author

This work was done in collaboration with:

Electrochemical Energy Laboratory, Massachusetts Institute of Technology, USA

Department of Material Science, University of Milano-Bicocca, Milano, Italy

MESA+ Institute of Nanotechnology, University of Twente, Netherlands

U.S. Department of Energy, National Energy Technology Laboratory, USA

SKKU Advanced Institute of Nanotechnology (SAINT), Center for Human Interface Nanotechnology (HINT), Sungkyunkwan University, Republic of Korea

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 Thomas Bahners¹ , Milan Kelch ², Jochen S. Gutmann 1, 3 Jörg Müssig²

1) Deutsches Textilforschungszentrum Nord- West gGmbH, Krefeld GERMANY

2) Hochschule Bremen, Bionik- Innovation- Centrum, The Biological Materials Group, Bremen GERMANY

3 ) Universität Duisburg- Essen, Physikalische Chemie and CENIDE, Essen GERMANY

Improvement of Fiber- Matrix Adhesion and Damping in Cellulose/Polyolefin Composite Materials by Means of Photochemical Fiber Surface Modification

  Fiber- matrix adhesion is an essential aspect for the mechanical properties of fiber- reinforced composites. But even if adhesion is strong, an abrupt change in mechanical properties at the fiber- matrix interface will result in reduced tenacity and insuffi cient damping. In contrast in nature , many plant structures exhibit graded transitions of mechanical properties between reinforcing elements and surrounding tissues [1].

Given this background, the scope of the presented study w a s to deposit organic thin- layers on reinforcement fibers by photo- polymerization, thus mimicking natural structures, and evaluate the potential to increase adhesion as well as damping behavior in bio- based fibers composites. Here, the focus is put on trend- setting composites based on textile structures made of regenerated cellulose fibers (viscose) embedded in polyolefins. These materials are in increasing demand – e.g. in food industry – but exhibit significant deficiencies in view of mechanical properties.

Diallylphthalate (DAP) and pentaeritritholtriacrylate (PETA) were employed as monomers for thin- layer formation. Making use of the characteristic absorption properties of these monomers, graft- co- polymerization as well as homo- polymerization processes can be initiated in a given monomer system by appropriate choice of the light source. Besides the hydrophobic nature of the established layers, it was known that mechanical and thermo- mechanical properties of poly- DAP and poly- PETA are influenced by monomer concentration and UV exposure time [2 ].

 Present results indicate a favorable effect on composite properties especially if PETA is used as the monomer. Fiber- matrix adhesion – characterized by pull- out tests as well as interfacial shear strength – were found to be influenced by parameters of the photochemical process, with monomer concentration and UV exposure time as the main factors.

 A significant finding shown by inverse gas chromatography (IGC) was that affinity of substances to the modified fiber surfaces – and the properties of this specific composite - were ruled by the water- octanol partition coefficient log p rather than by the related surface energies. This is believed to be due to the high water content and water sorption of the fibers. Accordingly, the shielding of the fiber surfaces by the deposited layers reduces water sorption and increases adsorption of substances with high log p as, e.g., benzene.

[1]     X. Wang, H. Ren, B. Zhang, B. Fei and I. Burgert, J. R. Soc. Interface 9 (2012) 988 – 996

 [2]    S.- L. Gao, Edith M ä der, A. Wego and E. Schollmeyer, Appl. Surf. Sci. 255 (2009) 9139 –9145.

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Ajay Kadiyala and Jayashree Bijwe; ITMMEC, Indian Institute of Technology Delhi, INDIA

Micro and Nano Sic Based Polyether Ether Ketone (PEEK) Coating on Stainless Steel: Tribology and Surface Energy Correlation Studies

Coatings to improve control friction and wear of components in severe applications are extensively find their way in engineering components. Poly-ether ether ketone (PEEK) has shown tremendous potential in applications such as bearing and slider materials. Considerable research on PEEK coatings using different techniques, such as flame spraying, plasma spraying, thermal spraying, printing and electrophoretic deposition have been reported. In the present work powder coating technique is employed. The coatings were characterized by contact angle, SEM.

Attempts have been made to explain frictional behavior in terms of surface energy. Frisbie et al. established the connection between chemical nature, adhesion and friction. The general rule is higher the surface energy better is adhesion and friction. The aim of the present work was to find out the effect of nano and micro SiC filler in PEEK coating of surface energy and relation with the friction performance. The ratio of surface energy/ hardness of coating was found to be proportional to the adhesion and frictional properties.

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Ludmila Boinovich and A.Emelyanenko; Institute of Physical Chemistry & Electrochemistry, Leninsky Prospect 31, Moscow 119991, RUSSIA

Surfactant Induced Deviation in Wetting Behaviour of Superhydrophobic Surfaces

E-mail: Boinovich@mail.ru

Recent advances in the control of surface wetting lead to the development of the diversity of functional materials with the special wettability for the industrial applications. Superhydrophobic surfaces have aroused researchers' intense interests due to their importance in both academic researches and practical applications. One of the key points for academic studies is the behavior of superhydrophobic surfaces in outdoor conditions of exploitation where the organic airborne contaminations are ubiquitously present. Typically such contaminations act as surfactants for aqueous medium/air and aqueous medium/solid interfaces. At the same time, for the superhydrophobic coatings fabricated on the basis of fluorine-containing hydrophobic agents such contaminations are surface inactive with respect to the superhydrophobic coating/air interface. Thus the evolution of wettability of superhydrophobic surfaces with respect to aqueous phases will be significantly affected by the surface energy of organic contaminations present in the atmosphere, their solubility in water, vapor pressure, their chemical structure.

In this talk we will demonstrate the intriguing peculiarities of contact angle behavior for water droplets atop of superhydrophobic surfaces in the presence of various type of surfactants and will discuss physics underlying the three phase equilibrium.

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Edward Bormashenko^1,2, Yelena Bormashenko², Roman Grynyov¹, Hadas Aharoni², Gene Whyman¹ and Bernard P. Binks3

1) Ariel University, Physics Department, P.O.B. 3, 40700, Ariel, ISRAEL

2) Ariel University, Chemical Engineering and Biotechnology Department , P.O.B. 3, 40700, Ariel, ISRAEL

3) Surfactant & Colloid Group, Department of Chemistry, University of Hull,

Hull. HU67RX. UK

Self-Propulsion of Liquid Marbles: Leidenfrost-Like Levitation Driven by the Marangoni Flow

Self-propulsion of liquid marbles filled with aqueous alcohol solutions and placed on a water surface is reported. The characteristic of velocity of the marbles is ca. 0.1 m/s. The phenomenon of self-propulsion is related to the Marangoni solutocapillary flow caused by the condensation of alcohol, evaporated from the liquid marble, on a water surface. The Marangoni flow in turn enhances the evaporation of alcohol from marbles. Addition of alcohol to the water supporting the marbles suppresses the self-propulsion. The propulsion of liquid marbles is mainly stopped by water drag. The velocity of the center of mass of marbles grows with the increase of the concentration of alcohol in a marble. The velocity of marbles’ self-propulsion is independent on their volume.

                 0 sec                                   60 sec                        90 sec

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Edward Bormashenko; The Ariel University Center of Samaria, 40700, Ariel, ISRAEL

Cold Plasma treatment of Liquid Surfaces

(Abstract not yet available)

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Edward Bormashenko; The Ariel University Center of Samaria, 40700, Ariel, ISRAEL

Electrical Charging of Surfaces under the Cold Plasma Treatment

(Abstract not yet available)

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Junqi Yuan, Jian Feng and Sung Kwon Cho; Dept. of Mechanical Engg. & Materials Science, University of Pittsburgh, Pittsburgh, PA 15261

Control of Floating Objects by Di-electrowetting

Cheerios effect is a common phenomenon named after observations that breakfast cereals floating in milk tend to be attracted to or repelled from the sidewall of bowl. This attraction/repulsion is driven by capillary forces and can be controlled by changing hydrophobicity (contact angle) of sidewall. Previously, we reported control of Cheerios effect by applying electrowetting to conductive liquid (water). However, this is not applicable for non-conductive (dielectric) liquids because electrowetting is not effective for dielectric liquids. We introduces di-electrowetting to change wettability of dielectric liquids and thus to control Cheerios effect. By controlling the contact angle of the sidewalls via di-electrowetting and thus distorting the adjacent interfaces, Cheerios effect can be controlled to manipulate floating objects in dielectric fluid. In this control, the titling angle of the sidewall is found to be critical. Theoretical calculation and experimental results are compared for various titling angles and applied voltages.

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Luisa Coriand¹, Nadja Felde^1,2, Susanne Pfeifenbring¹, and Angela Duparré¹

1) Fraunhofer Institute for Applied Optics and Precision Engineering, Albert-Einstein-Strasse 7, 07745 Jena, GERMANY

2) Friedrich-Schiller-University, Institute of Applied Physics, Max-Wien-Platz 1, 07743 Jena, GERMANY

Investigation of Oleophilic and Oleophobic Nanorough Surfaces Immersed in Air or Water

Functional surfaces with improved or novel properties are of great interest for a variety of applications such as self-cleaning effects minimizing the use of chemical detergents, and superoleophilic engineering surfaces reducing the friction of tribological systems. To achieve excellent wetting behavior, thorough enlightenment of the structural and wetting properties as well as of their relationship are required.

In the framework of this research, a wetting analysis method for underwater applications was developed. With this method, we can perform systematic investigations of oil wettability while the surfaces are immersed in water.

With the aim to investigate the relationship between the surface structure and oleophilic or oleophobic wetting behavior, surface roughness analysis was realized by atomic force microscopy allowing the calculation of power spectral density functions and wetting parameters. Furthermore, our wetting analysis methods for hydrophobic and hydrophilic wetting systems were used to characterize the wetting behavior of the oleophobic and oleophilic surfaces in air, too.

The investigation was performed for sol-gel coatings with a graded nano-roughness.

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M. Diallo¹, H. Duval¹, A. Koltsov², J.-M. Mataigne², M.-L. Giorgi¹

1) Laboratoire de Génie des procédés et matériaux (LGPM) CentraleSupélec, Université Paris-Saclay, Grande Voie des Vignes, 92295 Châtenay-Malabry Cedex, FRANCE

2) ArcelorMittal Global R&D - Automotive Products Centre, Voie Romaine BP 30320,57283 Maizières-Lès-Metz, FRANCE

Wetting Dynamics of Liquid Lead on Silica-patterned Iron

As well known, the spreading of a liquid droplet on a solid substrate is very sensitive to the presence of chemical heterogeneities on the solid substrate. In this study, wetting experiments with liquid lead on heterogeneous surfaces were performed at 450°C using the dispensed drop technique. The heterogeneous surfaces were composed of regular silica-patterned high-purity iron with different pillar sizes (from 5 to 500 µm) and spacing (from 5 to 500 µm). In this system, iron is wetted by liquid lead whereas silica is not.

The dynamic wetting of the liquid lead droplet on these heterogeneous surfaces was filmed at very short contact time (less than 1 s) with one image every millisecond, in order to measure the evolution of both the spreading diameter and the contact angle as a function of time. The contact angle hysteresis was deduced from these measurements. At the end of the spreading, the triple line of the solidified droplet was observed to be pinned on iron and to avoid the silica pillars (in a scanning electron microscope).

The experimental results obtained, namely the final contact angle, the contact angle hysteresis, the maximal spreading diameter and the dynamic contact angle, will be compared to calculations from models proposed in the literature.

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Alexandre M. Emelyanenko, Ludmila B. Boinovich, Kirill A. Emelyanenko, and Alexandr G. Domantovsky; A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky prospect 31 bldg. 4, 119071 Moscow, RUSSIA

E-mail: ame@phyche.ac.ru

Nanosecond Laser Micro and Nanotexturing for the Design of Superhydrophobic Coatings Robust to Long-term Contact with Water, Corrosion Active Medium, Cavitation, and Abrasion

An existing and emerging applications of laser-driven methods make an important contribution to the advancement in nanotechnological approaches for the design of superhydrophobic surfaces. In this study we describe the superhydrophobic coating on various metals, designed by nanosecond IR laser treatment with subsequent chemisorption of fluorooxysilane. We have shown that one of the most important steps in fabricating superhydrophobic coatings, i.e., surface texturing applied to impart multimodal roughness, may be simultaneously used for modifying the physicochemical properties of the thick surface layer of the substrate itself.

Coating characterization reveals extreme water repellency, chemical stability in long-term contact with water, durable corrosion resistance in concentrated potassium halides solutions and excellent durability of functional properties under prolonged abrasive wear and cavitation loads. Besides, coatings demonstrate self-healing properties after mechanical damage.

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Kirill A. Emelyanenko, Alexandre M. Emelyanenko and Ludmila B. Boinovich; A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky prospect 31 bldg. 4, 119071 Moscow, RUSSIA

E-MAIL ADDRESSES

 emelyanenko.kirill@gmail.com (K.A.E.);

 ame@phyche.ac.ru (A.M.E.)

 boinovich@mail.ru

The Description of Wetting Behavior of Alkanes on Water with Accounting for Water Solubility and Image Charge Effects

The wetting behavior of medium-chain hydrocarbons on water is analysed on the basis of the isotherm of disjoining pressure. Different types of surface forces, acting in the films of alkanes on water are discussed. It is shown that an important contribution to the surface forces originates from the solubility of water in alkanes. The equations for the distribution of electric potential inside the film are derived within the Debye–Hückel approximation, taking into account the polarization of the film boundaries by discrete charges at water-alkane interface and by the dipoles of water molecules dissolved in the film. On the basis of above equations we estimate the image charge contribution to the surface forces, excess free energy, isotherms of water adsorption in alkane film and the total isotherms of disjoining pressure in alkane film. The results indicate the essential influence of water/alkane interface charging on the disjoining pressure in alkane films, and the wettability of water surface by different alkanes is discussed.

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Frank M. Etzler, School of Pharmacy, LECOM, 1858 W. Grandview Blvd. Erie, PA 16509,

E-mail: fetzler@lecom.ed

Statistical Considerations for the Evaluation of Surface Free Energies from Contact Angle Data

Over the past few decades many papers have appeared in the literature concerning the determination of surface free energy of solids using either contact angles. Such calculations are based on models advanced by Owens and Wendt, Chaudhury, Good and van Oss, Chang and Chen as well as Kwok and Neuman. A perquisite for such calculation of surface free energy is the determination of contact angles of several liquids on the solid surface. Earlier, Kwok et al. stressed the need to obtain contact angles that conform to the assumptions required by Young's equation. [ Kwok et al, Langmuir 13, 2880 (1997)]. These authors also demonstrated that some liquids on certain surfaces failed to exhibit appropriate behavior. In many studies insufficient data are available to assess the quality of individual contact angle values. In this presentation, the statistical consequences of the choice of test liquids and the model chosen on the calculated surface free energy of various solids is explored. It is suggested that surface free calculations include an over determined data set and that a statistical analysis be performed to assess the quality of the measurements and the fit of the chosen models. Such analysis is important when the liquid interaction with the surface cannot be directly assessed and was done Kwok et. al.

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Michele Ferrari, Francesca Cirisano, Alessandro Benedetti, Libero Liggieri, Francesca Ravera, Eva Santini; CNR – Istituto per l’ Energetica e le Interfasi, 16149 Genova, ITALY

 Corresponding author: m.ferrari@ge.ieni.cnr.it

Amphiphobic Coatings for Protection in Seawater Environment

Highly hydro and oleophobic (amphiphobic) materials dedicated to the marine environment represent a relatively young field achieving growing interest as innovative solution, where technological and ecological aspects allow to be merged, taking into account the limitations imposed by international laws in terms of environment and protection.

In this work a superhydrophobic (SH) coating for applications has been characterized and tested in both laboratory and field conditions, since investigations in real seawater are crucial to evaluate the behaviour of SH surfaces because of a complexity not reproducible in laboratory. Because of the real conditions where the surface can operate, oleophobicity has been investigated.

Preliminary tests for wearing, thermal stress and durability have been also performed in order to study amphiphobic systems for different applications related to the marine environment.

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M.-L. Giorgi¹, J.-M. Mataigne², A. Koltsov²

1) Laboratoire de Génie des procédés et matériaux (LGPM) CentraleSupélec, Université Paris-Saclay, Grande Voie des Vignes, 92295 Châtenay-Malabry Cedex, FRANCE

2) ArcelorMittal Global R&D - Automotive Products Centre, Voie Romaine BP 30320,57283 Maizières-Lès-Metz, FRANCE

Influence of Kinetic Energy on Wetting of Steel Surfaces by Liquid Zinc in Two Conditions : Sessile Droplet and Continuous Galvanizing

The continuous galvanizing process is commonly used to form zinc coatings on steel sheet in order to increase resistance to corrosion. In this process, steel sheets are immersed in a molten Zn-Al (0.2wt.%) bath at about 450°C. The coating quality is mainly determined by the reactive wetting between the steel surface and the liquid metal.

In the industrial process, one key parameter is the steel substrate kinetic energy, related to its velocity in the galvanizing bath (around 2 m s^-1). Because of its high inertia, the liquid metal is dragged downwards by the steel strip movement at the entrance of the bath, which would correspond to a contact angle higher than 90°. Nevertheless, good wetting in such processes can hardly be understood without assuming the establishment of a small enough contact angle. Hoffmann and Cox-Voinov laws predict a dynamic contact angle less than 90° for the considered speed, and could be valid next to the steel strip where the amount of liquid to accelerate remains small enough so that inertia can be neglected. Consequently, a dimensional analysis will be proposed to compare inertia, capillary forces and viscous dissipation and to define characteristic lengths relevant of the considered system.

At the laboratory scale, dynamic wetting can be studied by means of the dispensed drop technique. The final contact angle of a liquid Zn – Al (0.2 wt.%) droplet dispensed on a steel substrate decreases significantly when the initial kinetic energy of the droplet is increased. The experimental results can be related to the reactions occurring at the interface between the steel and the molten metal at very short contact time.

A discussion on the role of the kinetic energy will be proposed in both cases (industrial process and laboratory scale).

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Savvas G. Hatzikiriakos; Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver BC, V6T 1Z3, CANADA

(e-mail: savvas.hatzi@ubc.ca)

Controlled-Superhydrophobicity on Metallic Substrates Using Fs Laser Ablation

Inspiration from nature, micro/nano scale structures and surface chemistry are the most effective parameters in making superhydrophobic surfaces. Irradiation of metallic surfaces using ultra-short pulse laser results in dual scale structure and changes in the surface chemistry. One of the most important problems in designing the superhydrophobic surfaces is creating a surface which Cassie-Baxter is the stable state on the surface. In this work, regular patterned structures are created in order to control the surface morphology and henceforth the level of superhydrophobicity. Various patterns are manufactured depending on the laser parameters such as scanning speed and laser fluence. Using the Gibbs free energy analysis of surface the equilibrium contact angle and hysteresis are calculated. The optimum surface parameters for a specified type of geometry can be determined by minimizing the Gibbs free energy. Alternatively, the effects of the geometrical details on maximizing the superhydrophobicity of the nanopatterned surface are also discussed in an attempt to design surfaces with desired wetting properties. An application of these metallic surfaces (stainless steel and titanium) in platelet adhesion and protein adsorption in biocompatibility applications will also be discussed.

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H. Jennissen; Institute of Physiological Chemistry, University of Duisburg-Essen, Hufelandstr. 55, D-45122 Essen, GERMANY

Complex and Imaginary Contact Angles: a Radically New Development for Advancing Our Understanding of Wetting, or Just a Whim of Applied Mathematics?

 In 2011 [1] we reported that Wilhelmy balance data of rough surfaces in the ultrahydrophilic/superhydrophilic range often cause forces leading to values of cos . > 1, which at that time had been termed as undefined and erroneous. We showed that the solution of this inequality is an imaginary number, which we interpreted as a dynamic imaginary contact angle, for the case that the real part of the underlying complex contact angle (i.e. intrinsic contact angle) is zero [2]. Concerning the question of a "physical basis", we felt that such a basis, which may as well be a "chemical basis", is important but not mandatory for an applied mathematical necessity (see [2]). This approach immediately enabled a novel analysis of superhydrophilic surfaces [3,4]. It should be recalled that according to current doctrine all superhydrophilic surfaces by definition have the peculiarity of possessing the same lowest contact angle of zero. According to our view characteristic imaginary or complex contact angles of different values can now be assigned to hitherto superhydrophilic surfaces [3,4]. Our suggestion of complex contact angles [2,5] is supported by the recent finding of a complex surface tension of water [6] suggesting this as their primary cause. Mathematical considerations indicate that this model may be too simple [7]. On the other hand a calculation of the underlying surface tension from an experimental dynamic complex contact angle . = 1¡ + 12.8i¡ [2] (i.e. a hyperhydrophilic surface) resulted in an apparent complex surface tension of * LV . ' = 73 + 0.28i mN/m [7], i.e. with a much lower imaginary part than the expected 17i (see [6]). Thus indeed, these results and their anticipated experimental support indicate a paradigm shift in wettability research.

 [1] Jennissen, H. P. (2011) Redefining the Wilhelmy and Young Equations to Imaginary Number Space and Implications for Wettability Measurements. Materialwiss. Werkstofftech. (Mater. Sci. Eng. Technol), 42, 1111-1117.

[2] Jennissen, H. P. (2014) A General Mathematical Form and Description of Contact Angles. Materialwiss. Werkstofftech. (Mat. Sci. Engineer. Technol), 45, 961-969.

[3] Lüers,S., Seitz,C., Laub,M., & Jennissen,H.P. (2013) On the Utility of Imaginary Contact Angles in the Characterization of Wettability of Rough Medicinal Hydrophilic Titanium. In Advances in Contact Angle, Wettability and Adhesion (Mittal,K.L., ed), pp. 155-172. Wiley-Scrivener, Salem, MA.

[4] Lüers, S., Seitz, C., Laub, M., & Jennissen, H. P. (2014) Contact Angle Measurement on Dental Implants. Biomed. Tech. (Berl), 59, 180-183, (DOI 10.1515/bmt-2014-4042).

[5] Jennissen, H. P. (2012) Hyperhydrophilic Rough Surfaces and Imaginary Contact Angles. Materialwiss. Werkstofftech. (Mater. Sci. Eng. Technol), 43, 743-750.

[6] Xiong, X. M., Chen, L., Zuo, W. L., Li, L. F., Yang, Y. B., Pang, Z. Y., & Zhang, J. X. (2014) Imaginary Part of Surface Tension of Water. Chin. Phys. Lett., 31, 076801-1 to-076801-4.

[7] Jennissen, H. P. (2015) On the Origin of the Imaginary Part of Complex Contact Angles. Materialwiss. Werkstofftech. (Mat. Sci. Engineer. Technol), 46, 786-795.

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Youhua Jiang, Wei Xu, Mohammad Amin Sarshar, Chang-Hwan Choi

Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey, USA

A Generalized Model of Advancing and Receding Contact Angles for Patterned Surfaces

Two different types of surfaces, including pillar and pore patterns, are tested for the measurement and the model development of advancing and receding contact angles of sessile droplets of water. The morphology and the dynamics of a distorted three-phase contact line during the advancing and receding motions are measured using reflective interference contrast microscope. Based on the experimental observation and the thermodynamic energy change during the motions, a global model that can theoretically predict the advancing and receding contact angles regardless of the surface patterns is formulated. According to the model, the contact angles are generally affected by the contact angles on a smooth (i.e., non-patterned) surface, the lengths of both a three-phase contact line and a leading liquid-gas interface, and how those interfaces move (e.g., shape and direction).

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Adya Karthikeyan, Sylvain Coulombe and Anne-Marie Kietzig; Chemical Engineering Department, McGill University, Montreal, CANADA

Surface Wetting and Surface Tension of Stable and Unstable Carbon Nanotube Nanofluids

Chemical Engineering Department, McGill University, Montreal, Canada

Nanofluids - the engineered colloidal suspension of nanoparticles in base fluids - have captivated the interests of researchers for various scientific applications. Properties such as viscosity, thermal conductivity and surface tension of colloids differs from those of the base liquids. A rich literature explains that the properties of nanofluids vary from those of the base fluid and that this deviation is dependent on the concentration of the nanoparticles dispersed. However, we found that the wetting properties of stable multiwall carbon nanotube (MWCNT) nanofluids are the same as those of the base liquids, independent of the MWCNT concentration.

MWCNTs were grown on a stainless steel mesh (SS 316) by thermal chemical vapor deposition. In order to produce stable nanofluids, MWCNTs were functionalized with oxygen containing functional groups using a simple plasma treatment. The functionalized MWCNTs were dispersed in two polar liquids, namely water and ethanol, to prepare stable nanofluids with MWCNT concentrations (per mass) of up to 120 and 210 ppm respectively. Unstable nanofluids were prepared by dispersing the as-synthesized MWCNTs in water. Also, to understand the influence of surfactants (the classic method of producing stable nanofluids) in the wetting of nanofluids, the surfactant sodium dodecyl sulfate was used to prepare nanofluids with as-synthesized MWCNTs in water. Surface tension of the stable nanofluids prepared with functionalised MWCNTs in water and ethanol was measured by the pendant drop method. The sessile drop contact angle was determined on ultra-flat silicon wafers for the stable, unstable and surfactant-stabilized nanofluids. Our experiments showed that surface tension and wettability remain constant for different concentrations of stable MWCNT nanofluids, however, it was observed that the contact angle varies for the agglomerated nanofluids and nanofluids stabilized with surfactants. Hence we conclude that the stability of nanofluids plays a key role in altering its properties.

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Ali Kibar¹, Ridvan Ozbay², and Chang-Hwan Choi²

1) Department of Mechanical and Material Technologies, Kocaeli University, Arslanbey Campus, Kocaeli, 41285 TURKEY

2) Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA

Air Bubble Detachment on Superhydrophobic Surfaces

In this study, the air bubbles growing and departing on superhydrophobic surfaces are examined experimentally. The spreading diameters and the contact angles in the case of growing bubbles and the receding diameters and the volumes in the case of departing bubbles were analyzed. When a superhydrophobic surface is submerged into the water, the surface is covered with a thin air layer. Therefore, a bubble grows on the superhydrophobic surface with little contact at the three phase contact line. The upward-facing superhydrophobic surface has a capacity to hold a large bubble on the surface. Then, the bubble pinches off the superhydrophobic surface with a large diameter.

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Kock-Yee Law; Research and Innovative Solutions, 27 Valewood Run, Penfield, NY 14526

(lawkockyee@gmail.com)

Wettable Slippery Surfaces. Self-cleaning Effect and Mechanism

The phenomenon of self-cleaning displayed by the Lotus leaf and many other plant and insect surfaces has attracted tremendous attention recently. Self-cleaning surface is usually superhydrophobic and non-wettable, and is characterized by a very large contact angle and a small sliding angle. Wettable surfaces, on the other hand, are characterized by small contact angles (e.g., ≤50^o). It is very uncommon to have surfaces that are highly wettable and slippery (sliding angles ≤10^o) at the same time. In this report, recent work on wettable, slippery surfaces from the author’s lab as well as others is reviewed.^1-8 The application of these surfaces as self-cleaning coating is presented. The fundamental mechanism leading to the slipperiness, despite of the small contact angles, is proposed and discussed.

References

1) Chen, W.; Fadeev, A. Y.; Hsieh, M. C.; Oner, D.; Youngblood, J.; McCarthy, T. J. Langmuir 1999, 15, 3395-3399.

2) Krumpfer, J. W.; McCarthy, T. J. Faraday Discuss. 2010, 146, 103-111.

3) Cheng, D. F.; Urata, C.; Masheder, B.; Hozumi, A. J. Am. Chem. Soc. 2012, 134, 10191-10199.

4) Urata, C.; Masheder, B.; Cheng, D. F.; Miranda, D. F.; Dunderdale, G. J.; Miyamae, T. Hozumi, A. Langmuir 2014, 30, 4049-4255.

5) Cheng, D. F.; Masheder, B.; Urata, C.; Hosumi, A. Langmuir 2013, 29, 11322-11329.

6) Kovacs, G. J.; Law, K. Y.; Zhao, H.; Sambhy, V. U.S. Patent 8,226,207, 2012.

7) Sambhy, V.; Law, K. Y.; Zhao, H.; Chugh, S. U.S. Patent 8,544,987, 2013.

8) Rabnawaz, M.; Liu, G.; Hu, H. Angew. Chem. Int. Ed. 2015, 54, 12722-12727.

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Choongyeop Lee, Seunggeol Ryu and Youngsuk Nam; Department of Mechanical Engineering, Kyung Hee University, Yongin-city, KOREA

Water Penetration Through Copper Mesh During Drop Impact: Influence of Surface Wettability

Here we show how water penetration through the copper mesh with microscale pore size is influenced by the surface wettability during drop impact by comparing the water penetration through a hydrophobic (HPo) mesh with that through a superhydrophobic (SHPo) mesh. In case of hydrophobic (HPo) mesh, the water penetration is well described by the force balance between the dynamic pressure upon impact and the capillary force. However, additional water penetration route appears on SHPo mesh during a lift-off of water droplet in addition to one upon drop impact. Due to this additional penetration mechanism, it is shown that the SHPo mesh is more easily penetrated by the impacting drop over HPo one and reducing the pore size does not necessarily lead to the enhanced resistance to the water penetration. We study the origin of this additional water penetration based on dynamic behavior of the water droplet right before the penetration.

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Junghoon Lee, Youhua Jiang, Chang-Hwan Choi; Department of Mechanical Engineering, Stevens Institute of Technology, Castle Point on Hudson, New Jersey 07030

Oil-Impregnated Anodic Aluminum Oxide Layers for Omniphobic Surfaces

Oil-impregnated surfaces have a promising potential for non-stick, self-healing, anti-icing and anti-bacterial surface. We designed and tested various types of oil-impregnated anodic aluminum oxide (AAO) layers, and demonstrated their applications to omniphobic and non-stick surfaces for metallic substrates. Four types of AAOs, including typical nanoporous AAOs with small or large pores, and pillared AAOs with single or bundled pillars, were fabricated for the oil-impregnation. Perflorinated oil was impregnated into the nanostructures of the hydrophobized AAOs to have a high affinity with the perfluorinated oil. We examined the omniphobic properties of the oil-impregnated AAO layers, compared with the conventional air-impregnated AAO layers, by testing liquids with different surface tensions. The nanoporous AAO with a large diameter stably immobilized the perflorinated oil in the nanostructures, exhibiting robust slippery behaviors for both high and low surface tension liquids. In contrast, the nanoporous AAO with a small diameter or the pillared AAOs showed limited durability for slipperiness.

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Eric Loth; University of Virginia, Room 308 MEC, 122 Engineer's Way P.O. Box 400746, Charlottesville, VA 22904

Micro-dynamics of Wetting (High Spatial and Temporal Resolution)

(Abstract not yet available)

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Lasse Makkonen; Principal Scientist, VTT Technical Research Centre of Finland, Box 1000, 02044 VTT, FINLAND

Young’s Equation Revisited

Young’s construction for the contact angle at a three-phase intersection forms the basis of wetting and capillarity theory. Here, compelling evidence is found from recent experimental results on the deformation of a soft solid at the contact line, and displacement of an elastic wire immersed in a liquid, on that no active surface tensional force exists on a solid. Consequently, Young’s equation cannot be interpreted by a balance of surface forces. This experimental result is explained conceptually and is consistent with the thermodynamic explanation of sliding friction. Young’s equation is then derived by interpreting it by surface energies. This derivation shows that the a priori variable in finding the equilibrium is not the position of the contact line, but the contact angle itself. This provides the explanation for the pinning of a contact line and opens a way to explain related phenomena, such as the contact angle hysteresis.

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Lasse Makkonen; Principal Scientist, VTT Technical Research Centre of Finland, Box 1000, 02044 VTT, FINLAND

A Quantitative Theory of Contact Angle Hysteresis

The origin of contact angle hysteresis has been controversial because Young’s equation predicts no contact line pinning on a homogeneous surface. Here, a theory of contact angle hysteresis is derived from first principles. It is shown that contact angle hysteresis and contact line pinning are fundamental phenomena that occur already on an ideal smooth surface. The theory is quantified by utilizing Berthelot’s rule. The model is corroborated by experimental data with a large number of solid-liquid combinations. This fundamental theory is then used to model contact angles hysteresis on a textured surface. These theoretical results are also in quantitative agreement with experimental data.

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Lasse Makkonen; Principal Scientist, VTT Technical Research Centre of Finland, Box 1000, 02044 VTT, FINLAND

Determining the Surface Energy of a Solid by Contact Angles

For two centuries, solid surfaces have been characterized by measuring the contact angle of a liquid at a three-phase contact line. Quantification of the surface energy of a solid has required the use of Zisman’s method, where measurements using a variety of different liquids are required, or empirical relationships, such as Neumann’s equation of state. Here, it is shown that the connection between the surface energy and the static and dynamic contact angles can be found by a purely physical theory. This theory allows determining both the solid-vapour and solid-liquid interface energies from a measurement of a contact angle of a single liquid. This is demonstrated by showing that, for non-polar solids, the theory provides values of the solid surface energy that are at least as consistent as those obtained by the empirical fitting formulas.

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Ridvan Ozbay¹, Ali Kibar², and Chang-Hwan Choi¹

¹) Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, New Jersey, UNITED STATES

²) Department of Mechanical and Material Technologies, Kocaeli University, Kocaeli, TURKEY

Bubble Adhesion on Superaerophobic Surfaces: Effects of Surface Morphology

The adhesion force of captive air bubbles on micropillared superaerophobic (i.e., superhydrophilic) surfaces is experimentally investigated. Particularly, the effects of surface morphology on superaerophobicity are investigated systematically using micropillared patterns with varying solid fractions. The sliding angle and the adhesion force of an air bubble on the surfaces are analyzed for the superaerophobicity. Theoretically, the adhesion force of an air bubble on an inclined surface depends on the contact width and the contact angles at the uphill (advancing) and downhill (receding) sides, and it is balanced by other external forces such as buoyant force and Laplace pressure. Results shows that contact angle hysteresis and the adhesion force reduce with the decrease in a solid fraction of the micropillared surfaces and that superaerophobicity can further be promoted by the decrease in a solid fraction due to a thin water layer formed between the bubble and the surfaces.

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D. Panchanathan, G. Kwon, K. K. Varanasi, G. H. McKinley; Dept. of Mechanical Engg., MIT, Cambridge, U.S.A.

Quantifying the Kinetics of Photocatalysis on Nanoporous Titania Surfaces using Contact Angle Goniometry

The photocatalytic and hydrophilic nature of TiO₂ (titania) coatings can be exploited to ensure preferential wetting of water over oil under ultraviolet (UV) irradiation and this provides a mechanism for membrane surface recovery from fouling events. In this work, we studied the photoinduced cleaning ability of nanoporous titania coatings in oil-water environments for fouling recovery in oil/water applications. Fouled hydrophobic surfaces were irradiated with UV light in a fully-submerged oil-water environment to photocatalytically decompose the organic pollutant (oil phase) and restore hydrophilicity. The kinetics of this conversion from hydrophobicity to hydrophilicity were studied in situ under various UV intensities using goniometric measurements. A simple adsorption-photocatalysis model (LuCY – Langmuir-Hinshelwood Cassie-Baxter Young) was developed to quantitatively interrelate two surface phenomena - photocatalysis and wetting. In this way, we can quantify the kinetics of photocatalysis on nanoporous surfaces in situ using wetting data. We also demonstrate that UV irradiation can be used for in situ removal of oil fouling from a mesh coated with TiO₂ nanostructures. The calibrated kinetic model can subsequently be applied to optimally control wetting recovery in fouling remediation and droplet coalescence applications.

Sponsorship: King Fahd University of Petrolem and Minerals (KFUPM)

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Keun Park* and Hyun-Joong Lee; Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul, KOREA

*Corresponding author: Email: kpark@seoultech.ac.kr

Development of Superhydrophobic/hydrophilic Hybrid Surface by Selective Micropatterning and Electron Beam Irradiation

In this study, surface wettability of polycarbonate (PC) films was modified using selective micropatterning using ultrasonic imprint lithography and electron beam irradiation. To modify surface wettability selectively in a specified region, these treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle. The semi-hydrophobic PC film was modified to create a superhydrophobic state by virtue of the selective micropatterning and fluorinate coating. The electron beam irradiation had an opposite effect so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in contact angle on a single surface, as high as 107.7°, and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability.

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Davide Rossi¹ , Antonio Bettero¹, Nicola Realdon¹, Paola Pittia²

1) Department of Pharmaceutical and Pharmacological Sciences, University of Padova, ITALY

2) Department of Bioscience and Technology of Food, Agriculture and Environment, University of Teramo, ITALY

 Development of a Method for Contact Angles Measurements at

 Perfluoropolyether/perfluoropolyether Interface Employing Fomblin Hc/25̈pfpe as “ Fluid Film ” for Surface Energy Characterization of Some Water Solutions

 The fluoropolymer Fomblin HC- 25 perfluoropolyether ’ s (PFPE) is a biocompatible fluid used to characterize topical formulations in contact on skin & mucous membranes. It was used for the first time as liquid test for topical formulations surface energy characterization and for the development of a new PFPE ‘ s tensiometric marker used to evaluate the quality of thermal muds (TVS mud index ñ ). In this work a procedure enabling to use PFPE fluoropolymer in the form of a solid trial film (named “ fluid film ” ) being based on its self- repellent nature was developed. The measurement of the contact angle at PFPE/PFPE fluid film ’ s (PFPEf) interface and the consequent determination of the surface- energy profile of the Fomblin HC- 25 PFPEf and its dispersed and polar components, showed PFPE capacity to perform itself either as a solid ( “ fluid film ” ) or as a liquid. In the light of these outcomes, the method for the characterization of Fomblin HC- 25 (PFPE) has been defined with the acronym of Solid Like Method (SLM) and consented also to characterize the surface free energies of aqueous glycerin & sodium chloride solutions proving its dual capacity for solid & liquid tests. This new approach is quick and easy to use and open new perspectives in tensiometric application allowing the determination of surface energy components of natural or artificial fluids by avoiding the influence of roughness and frictions factors at the interface on contact angles measurements.

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Hernando S. Salapare III* and Frédéric GUITTARD; Université de Nice-Sophia Antipolis, CNRS, Laboratoire de Physique de la Matière Condensée (LPMC), UMR 7336, Parc Valrose, 06100 Nice, FRANCE

*Corresponding Author. E-mail: salapare@unice.fr

Superhydrophobicity of Candle Soot Film Deposited on Rf Plasma-treated Poly(ethylene Glycol-co-1,3/1,4 Cyclohexanedimethanol Terephthalate) (PETG)

Poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) (PETG) surfaces were microstructured via oxygen plasma produced in reactive ion etching (RIE) configuration of an RF plasma device. The changes on the sample surfaces were determined by water contact angle measurements and profilometry. Surface wettability was enhanced for the plasma treated samples together with an increase in the surface roughness for the plasma treated samples as compared to the control samples due to surface etching. Superhydrophobic candle soot films with a maximum water contact angle of 164° were deposited via a simple flame method on the control and plasma-treated samples. Durability tests on superhydrophobic surfaces defined by Malavasi et al. were modified for the study. Durability tests such as water, ethanol, HCl acid, NaOH, and NaCl immersions were performed on the samples with the results demonstrating that samples with higher surface roughness values exhibited better candle soot film adhesion to the samples. [2]

References:

[1] I. Malavasi, I. Bernagozzi, C. Antonini, M. Marengo, Surface Innovations 3 (2015) 49-60.

[2] H.S. Salapare III, F. Guittard, Surface Innovations 3 (2015)192-195.

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D. K. Sarkar; Centre Universitaire de Recherche sur l’Aluminium (CURAL), Université du Québec à Chicoutimi, 555 Boulevard de l’Université, Chicoutimi, Québec, CANADA G7H 2B1

EMAIL: dsarkar@uqac.ca

Studies of Corrosion Properties of Nanostructured Superhydrophobic Thin Films on Metals

Superhydrophobic thin films were fabricated both on aluminum and copper substrates by chemical process namely, (i) chemical etching followed by passivation with organic acid molecules; (ii) electrophoretic deposition (EPD) of functionalized ZnO nanoparticles and (iii) electrodeposition of organic-inorganic composite materials. The physical and compositional analyses of the deposited thin films were characterized by SEM/EDX, ATR, XRD as well as contact angle goniometer. Furthermore, the corrosion properties of the superhydrophobic thin films were analyzed with both polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl aqueous solutions. The results demonstrate that the superhydrophobic thin films on both aluminum and copper substrates display better anti-corrosion properties than the as-received metal substrates. The comparison of results pertaining to the compositional and corrosion properties of these thin films will be discussed in this work.

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Mohammad Amin Sarshar, Chris Swartz, Chang-Hwan Choi

Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA

Icephobicity of Superhydrophobic Surfaces: Effects of Environmental Conditions

Four superhydrophobic surfaces with different surface roughnesses and wettabilities are tested for icephobicity including both anti-icing and de-icing properties. Anti-icing test is conducted utilizing an icing wind tunnel which allows to observe how much ice gets accumulated on the surfaces in a dynamic condition (i.e., with forced supercooled water droplets by wind). For the de-icing test, sessile droplets of water are frozen on the surfaces in a static condition (i.e., no wind) and the adhesion force between the frozen droplets and the surfaces were measured using a force sensor. Results show that whereas a superhydrophobic surface with a less receding contact angle delays the ice accumulation in a dynamic condition more effectively, the same surface can exhibit higher adhesion force for the ice grown in a static condition. The distinct behaviors are attributed to the different freezing mechanisms affected by the environmental conditions.

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Sara L. Schellbach, ¹* Sergio N. Monteiro² and Jaroslaw W. Drelich¹*

1) Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA

2) Military Institute of Engineering, IME, Praça General Tiburcio, 80, Praia Vermelha, Urca, 22290-270 Rio de Janeiro, RJ, BRAZIL

A Novel Method for Contact Angle Measurements on Natural Fibers having Non-Uniform Cross Sections and Rough Surface

Natural fibers are attractive alternatives to synthetic fibers as reinforcement in the formation of polymeric composites due to their biodegradation, low price, low density and good insulation properties. Non-uniformity of natural fiber dimensions, cross-sections and rough surfaces cause the characterization of physical and surface properties, including wettability, to be more challenging than for synthetic fibers. Traditional methods of contact angle measurements on fibers, such as drop-on-fiber and tensiometry, are difficult to apply to natural fibers and typically do not conclude with reproducible contact angle data. A novel method of contact angle measurements on fibers is proposed. In this method, a liquid column is formed between two fibers spaced by a fraction of a millimeter and the contact angle is analyzed for menisci at both sides of the liquid column. In this study, advancing and receding water contact angle measurements were conducted for commercially available fibers of hemp, curaua, fique, jute, piassava, pineapple, ramie and sisal. All the natural fibers were found to be weakly hydrophobic, with the advancing water contact angles typically between 39 to 50 degrees and contact angle hysteresis varied from 2 to 30 degrees.

*Corresponding authors

SLS - Email: slschell@mtu.edu; JWD - Email: jwdrelic@mtu.edu, Phone: 1-906-487-2932

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Michael Schmitt and Florian Heib; Physical Chemistry, Campus B 2 2, Saarland University, 66123 Saarbrücken, GERMANY

E-mail: mic.schmitt@mx.uni-saarland.de

Fundamentals of Reproducible/enhanced Contact Angle Analyses

Characterization of wetting behaviour by contact angles of sessile drops (horizontal and inclining plate geometry) is essential in science and in industry. One of the most important challenges in this area is to build a standard method of measuring even more analysing dynamic contact angles in a reproducible manner. In other words the presentation deal with the question “What is the most appropriate to measure contact angle?”

The first part of this presentation will provide you with the necessary information concerning the restrictions of most commercial image/CA analysis. This problem based on the image transformation/fitting can be solved by the developed high-precision drop shape analysis, HPDSA [1].

Within the second part the manual analysis will schematically be compared with the different automatic procedures which were recently developed [2][3]. These statistical procedures lead e.g. to advancing and receding angles (specific angles) which are not liable to subjectivity and allow the surface properties to be described/analysed much more in detail. The first procedure based on statistical analysis can be called enhanced manual analyses which have the additional benefit to be able to investigate the distributions of the CA events. The second procedure is the average “behaviour” of the CA measurement which is investigated by fitting the raw data and averaging/simulating. Thereby the whole measurement can be stored with only four parameters. Even specific angles can be obtained from these adaptive functions. Comparing the data with the function leads to the possibility to analyse the surface in detail[1].

[1] M. Schmitt and F. Heib, J. Chem. Phys., 2013, 139.

[2] M. Schmitt, K. Gross, J. Grub and F. Heib, J. Colloid Interface Sci., 2015, 447, 229-239.

[3] M. Schmitt, J. Grub and F. Heib, J. Colloid Interface Sci., 2015, 447, 248-253.

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Daniel Scholz; DataPhysics Instruments GmbH, Raiffeisenstrasse 34, 70794 Filderstadt, GERMANY

Measuring Adhesive Forces of Liquids on Solid Surfaces using a Tensiometer

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Digvijay Singh and Robert Baier; State University of New York at Buffalo, Buffalo, NY

Contact Angle and Wettability Correlations for Bioadhesion to Reference Polymers, Metals, Ceramics and Tissues

A new preparation of a clinically valuable bioadhesive, actively glutaraldehyde-tanning bovine albumin gel (BioGlueTM ), allowed an examination of the specific surface characteristics of reference materials influential in biological adhesion. The expected direct correlation with water wettability was disappointing, while the experimental Critical Surface Tension (CST) values empirically determined for the substrata comprising both polar and dispersive surface features showed a superior and linear correlation. It was surprising that the presence of active glutaraldehyde cross-linking did not produce covalent binding to either fresh or native tissues of blood vessels, ureters or pericardium, and that the shear release strengths of between 20 & 30 psi were similar for all materials with intermediate surface energies above 30 mN/m. Two interesting anomalies invite further analysis: [1] Stronger-than-predicted binding occurred to Pyrolytic Carbon (the blood-compatible material of synthetic heart valves), tentatively attributed to the pi-pi bonding of superficial ring structures from both adhesive & adherend, and [2] weaker-than-expected bonding occurred to polished metallic alloys of titanium and steel (used in orthopedic appliances), tentatively attributed to a smeared Beilby layer of interfacial oxides removable by slight roughening. 

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Birgitt Boschitsch Stogin, Xianming Dai, and Tak-Sing Wong;

Department of Mechanical and Nuclear Engineering and the Materials Research Institute, The Pennsylvania State University, University Park, PA, USA

Wenzel Wetting on Slippery Rough Surfaces

Liquid repellency is an important surface property used in a wide range of applications including self-cleaning, anti-icing, anti-biofouling, and condensation heat transfer, and is characterized by apparent contact angle (???) and contact angle hysteresis (????). The Wenzel equation (1936) predicts ??? of liquids in the Wenzel state [1], and is one of the most fundamental equations in the wetting field. However, droplets in the Wenzel state on conventional rough surfaces exhibit large ????, making it difficult to experimentally verify the model with precision. As a result, precise verification of the Wenzel wetting model has remained an open scientific question for the past ~79 years. Here we introduce a new class of liquid-infused surfaces [2, 3] called slippery rough surfaces?surfaces with significantly reduced ???? compared to conventional rough surfaces?and use them to experimentally assess the Wenzel equation with the highest precision to date.

[1] R.N. Wenzel, Ind. Eng. Chem. 28: 988-994 (1936).

[2] T.S. Wong et al., Nature 477: 443 ? 447 (2011).

[3] X. Dai, B.B. Stogin, S. Yang, T.S. Wong, ACS Nano 9: 9260 ? 9267 (2015).

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Hana Sourková; Technical University of Liberec, Faculty of mechatronics informatics and interdisciplinary studies, Studentská 1402/2, Liberec:  461 17, CZECH REPUBLIC

Surface Tension Characterization of Plasma Treated Powders as a Process Control for Industrial Application

Determination of surface tension is a standard control method of materials treated by plasma before adhesive bonding or varnishing. Fast and simple methods are used in industry during process control e.g. contact angle analysis or determination of surface energy by test inks. These methods can be successfully used for solid and compact materials. Difficulties occur while trying to establish surface tension at powders. Several methods can be used to determinate surface characteristics of powder materials. Melting a powder to a plate is one of the methods enabling an application of the same techniques as for solid materials. Washburn is another method used to characterize surface wettability and is directly specified for powder materials. These methods cannot be used for all materials and some are not suitable for industrial application due to time consumed and high costs. Fast and reliable method is necessary in order to quality control during production of plasma treated powders. For a reliable process control a method independent on variable powder parameters e.g. particle size distribution and-or particles roughness is desired. Detailed analysis of a large amount of Washburn data from the control of a serial production was performed. The results from Washburn data were compared with contact angle measurements on the powder adhered on an adhesive tape. Ability of powder to disperse in water was also tested and ECSA analyses was performed on selected samples. Based on this analyses a method for on-line process control was proposed.

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Konrad Terpiłowski¹ Marta Tomczyńska-Mleko², Stanisław Mleko³ and Emil Chibowski¹

 1) Department of Physical Chemistry-Interfacial Phenomena, Maria Curie Sklodowska University, Lublin, POLAND

2) Institute of Plant Genetics, Breeding and Biotechnology, University of Life Sciences in Lublin, POLAND

3) Department of Milk Technology and Hydrocolloids, University of Life Sciences in Lublin, Poland

The Surface Properties of Biopolymers Obtained with the Presence of Gluten

The aim of the research was to obtain biopolymers based on wheat gluten, whey protein concentrate (WPC) and montmorillonite (MON). Ternary biopolymers were formed as heat-induced gels and they were hardened by water evaporation. Adding 7 % of MON and 5 % WPC to gluten caused ca. four times higher values of storage modulus. Increased moduli values with adding MON and WPC to gluten were probably caused by reinforcing effect of MON, which decreased mobility of gluten chains and possible interactions between gluten and whey proteins by disulphide interchange. Increase in gluten protein concentration and addition of WPC and MON caused increase in viscosity measured by dissipation of ultrasound vibrations. Evaporation of water from the gels formed very hard material with high puncture force values. Obtained gels wered very plastic and it was easy to form any type of shapes. They could be used to produce biodegradable pottery (e.g. flowerpots) with the mechanical properties similar to non-degraable clay products. Surface properties of obtained materials were investigated by contact angle measurements, determination of apparent surface free energy. Topography of obtained materials were determined by optical profilometry and SEM microscopy. Chemical surface composition were investigated by XPS technique.

References:

M. Wesołowska-Trojanowska, M. Tomczyńska-Mleko, K. Terpiłowski, M. Kawecka-Radomska, S. Mleko, Ternary Biopolymer Based on Wheat Gluten, Whey Protein Concentrate and Montmorillonite, J. Inorg Organomet Polym, 26 (2016) 555-562

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Salma Falah Toosi¹, Sona Moradi¹, Narges Hadjesfandiari², Jayachandran N. Kizhakkedathu^2,3, and Savvas G. Hatzikiriakos¹

1) Department of Chemical and Biological Engineering,

2) Centre for Blood Research and Department of Chemistry,

3) Department of Pathology and Lab Medicine,

The University of British Columbia, Vancouver BC, V6T 1Z3, CANADA

The Effect of Superhydrophobicity on the Bacterial Adhesion on Polymeric Surfaces

Dual scale, superhydrophobic nano/micro structures were fabricated on various polymeric surfaces (PTFE, PLA and PE) by using a simple one step femtosecond laser ablation method. Several distinctly different micro/nano-patterns were fabricated including uniaxial and biaxial ones. The effect of femtosecond laser irradiation process parameters (fluence, scanning speed and beam overlap) on the surface morphology and thus the wetting properties were studied in details by using profilometry, SEM, XPS, and CA analysis. A hot-embossing process was also developed to nano-imprint the SS and PTFE laser-ablated morphologies onto the surface of any desired polymeric substrate, including PE and PLA rendering most of them superhydrophobic. The effect of superhydrophobicity on the adhesion of both gram negative and gram positive bacteria on various polymeric surfaces was investigated.

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Pan Guo, Yusong Tu, Jinrong Yang, Chunlei Wang, Nan Sheng, and Haiping Fang; College of Physics Science and Technology, Yangzhou University, 88 South University Ave., Yangzhou, Jiangsu 225009, P.R. CHINA

Water-COOH Composite Structure with Enhanced Hydrophobicity Formed by Water Molecules Embedded into Carboxyl-Terminated Self-Assembled Monolayers

By combining molecular dynamics simulations and quantum mechanics calculations, we show the formation of a composite structure composed of embedded water molecules and the COOH matrix on carboxyl-terminated self-assembled monolayers (COOH SAMs) with appropriate packing densities. This composite structure with an integrated hydrogen bond network inside reduces the hydrogen bonds with the water above. This explains the seeming contradiction on the stability of the surface water on COOH SAMs observed in experiments. The existence of the composite structure at appropriate packing densities results in the two-step distribution of contact angles of water droplets on COOH SAMs, around 0° and 35°, which compares favorably to the experimental measurements of contact angles collected from forty research articles over the past 25 years. These findings provide a molecular-level understanding of water on surfaces (including surfaces on biomolecules) with hydrophilic functional groups. It is worth noting that composite structures may also exist on many other surfaces with hydrophilic groups, which extends our understanding of the behavior of water on surfaces, including surfaces on biomolecules.

1.     P. Guo, Yusong. Tu, J. Yang, C. Wang, N. Sheng, and H. Fang, Water-COOH Composite Structure with Enhanced Hydrophobicity Formed by Water Molecules Embedded into Carboxyl-Terminated Self-Assembled Monolayers, PRL 115, 186101 (2015)

2.     Chunlei Wang, Bo Zhou, Yusong Tu, Manyi Duan, Peng Xiu, Jingye Li, and Haiping Fang, Critical Dipole Length for the Wetting Transition Due to Collective Water-dipoles Interactions, Sci. Rep. 2, 358 (2012).

3.     Chunlei Wang, Binghai Wen, Yusong Tu, Rongzheng Wan, and Haiping Fang, Friction Reduction at a Super-Hydrophilic Surface: Role of Ordered Water, The Journal of Physical Chemistry C 119, 11679 (2015).

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G. Paz-Gómez¹, M.J. Otero-Díaz¹, J.A. del Caño-Ochoa², Clara Moyano³, G.R. Guerrero², M.A. Cabrerizo-Vílchez¹, M.A. Rodríguez-Valverde¹

1) Biocolloid and Fluid Physics Group, Department of Applied Physics, University of Granada, SPAIN.

2) Department of Mechanical Engineering, University of Cordoba, ctra. Madrid-Cádiz km 396, E-14071 Córdoba (SPAIN).

3) Parker Instrumentation Products Division Europe, UNITED KINGDOM.

Water-Repellent Non-stick Coatings

In this work we have modified commercial non-stick coatings by sandpaper abrasion and sandblasting, separately, to reach water-repellency properties. We used a fluoropolymer coating supplied by Whitford Worldwide. We evaluated two types of coatings. The PTFE-based coating was sintered on aluminium surfaces at different temperatures and next polished with sandpaper of different grit number. Before polishing, we measured the roughness, contact angle hysteresis, critical sliding angle, hardness and thickness of the “smooth” sintered surfaces. We also prepared the same coating but sintered at a fixed temperature and sandblasted with two types of sand to reach the water repellency. We measured the topography parameters and water tensile adhesion of the water-repellent coatings by using the number of bounces of a bouncing drop. We classified the final non-stick coatings as their water repellency and we justified this behavior from the sintering temperature (initial roughness and hardness), grit number and sandblasting conditions (type and size of abrasive particle, blasting time).

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M. F. Ismail and Prashant R. Waghmare; Interfacial Science and Surface Engineering Lab, Department of Mechanical Engineering, University of Alberta, Edmonton, CANADA, T6G 2G8

Universality in Freezing of Asymmetric Drop

We present the experimental and theoretical analysis of asymmetric water droplet freezing phenomenon. The focus is to demonstrate the systematic variations in the asymmetric frozen drop and validate the universality of singularity in pointy shape frozen drop in such asymmetric drops. We observe that the tip angle universality is also valid for asymmetry drop where the lateral shifting of pointy tip is noticed. The proposed ‘two-triangle’ model quantifies the location of the tip as a function of asymmetry of the drop that shows good agreement with the experiments. Finally, we demonstrate the universal law for tip shifting and height of the asymmetric frozen drop based on the observed experimental results and theoretical analysis.

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Chunlei Wang; Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jialuo Road 2019, Jiading Shanghai, Shanghai 201800, CHINA

Ordered Water Monolayer That Does Not Completely Wet Water and molecular-scale hydrophilicity at Room Temperature

Viewed macroscopically at room temperature, water always completely wets other water due to the formation of hydrogen bonds. In 2009, based on molecular dynamics simulations, we predicted the phenomenon of a liquid water droplet on a water monolayer, which has been termed as “ordered water monolayer that does not completely wet water” at room temperature [1,2]. This can be attributed to that the ordered water structure reduced the possibility of hydrogen bond formation between the ordered water and the molecules above this monolayer. Recently, scientists experimentally and theoretically found the similar phenomenon on sapphire c-plane surface and TiO₂ surface, the talc, hydroxylated Al₂O₃, hydroxylated SiO₂ and some metal surfaces [3]. This ordered water monolayer can be used to reduce the surface friction at the superhydrophilic surfaces [4]. We also observed the phenomenon “ordered ethanol monolayer does not completely wet ethanol” at room temperatures on a simple model surface based on MD simulations[5].

[1] Wang and Fang et al., Phys. Rev. Lett. 103,137801 (2009)

[2] Wang and Fang et al. J. Phys. Chem. C 115, 3018 (2011)

[3]Xu and Wang et al., J. Phys. Chem. C 119, 20409 (2015)

[3] Wang,and Fang et al. J. Phys. Chem. C 119, 11679 (2015)

[4] Wang and Fang et al. J. Phys. Chem. C, 118,1873 (2014)

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Zuankai Wang; Department of Mechanical and Biomedical Engineering, City University of Hong Kong, HONG KONG

Bioinspired Materials: the Quest for the Maximum Water Repellency and Multifunctional Application

(Abstract not yet available)

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D.G. Waugh, J. Lawrence, A. Gillett and C.H. Ng; Laser Engineering and Manufacturing Research Group, Faculty of Science and Engineering, University of Chester, Thornton Science Park, Pool Lane, Ince, Chester CH2 4PU, UK

Laser Surface Treatment: Modulating Wettability Characteristics of Materials to Control Biological Cell Adhesion and Growth

Lasers offer the ability to modify the surfaces of materials both topographically and chemically. Such laser surface treatments can be employed to modulate the wettability and adhesion characteristics of numerous materials. This work details how lasers can be used to surface treat both metals and polymers for the manipulation of the wettability characteristics and details the subsequent effects on biological cell adhesion and growth. The laser-modified surfaces were analyzed using 3D surface profilometry to ascertain an increase in surface roughness when compared to the as-received sample. The wettability characteristics were determined using the sessile drop method and showed variations in contact angle. For Polytetrafluoroethylene (PTFE), it was seen that the laser surface treatment gave rise to a super-hydrophobic surface with contact angles of up to 150° being achieved. For nylon 6,6, it was observed that the contact angle was modulated approximately +10° for different samples which could be attributed to a likely mixed state wetting regime. The surface morphology and composition of the materials were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. The success of enhanced adhesion and spreading of mesenchymal stem cells (MSCs) and osteoblast cells on laser surface treated samples, when compared to as-received samples, is evidenced and discussed in this work.

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Ming Jin, Daniel Frese, Carsten Scheithauer, Thomas Willers

KRÜSS GmbH, Borsteler Chaussee 85, 22453 Hamburg, Germany

Raymond Sanedrin; KRÜSS USA, 1020 Crews Road, Matthews, NC 28105, USA

Replacing the Solid Needle by a Liquid One When Measuring Static and Advancing Contact Angles

Generally, the optical determination of static and advancing contact angle (CA) is made on drops applied or extended, respectively, onto a substrate through the use of thin solid needles. Although this method is used extensively, this way of dosing can be time consuming, cumbersome and if not performed meticulously can lead to erroneous results. Herein, we present a recently developed way of applying drops onto substrates using a liquid jet produced by an elaborate dosing system acting as a “liquid needle”, compare Figure. This is a fundamentally different way of dosing. To the best of our knowledge, so far it was not possible to observe comparable CA results on the same substrates when using a liquid jet dosing or the traditional way of drop deposition. We present a static contact angle study on 14 different surfaces with four different liquids utilizing the two different dosing systems. We find and explain that drops deposited with the here used specially designed liquid jet indeed have precise CAs as the ones deposited with the traditional needle based system.

Furthermore, we demonstrate how this liquid needle facilitates advancing contact angle measurements with a high speed of the contact line of 1.1mm/s. We will compare those results to data from dynamic Wilhelmy CA measurements, where the speed is significantly smaller (3.3μm/s).

The liquid needle has advantages in terms of measurement speed and more importantly in control of the dosing process over the traditional needle dosing system. Possible errors caused by the drop deposition as they can occur for the solid needle dosing are intrinsically excluded thus resulting in a better reproducibility. Further, it facilities drop deposition on super liquid-repellent surface not being possible with solid needles. Therefore, we believe replacing the solid needle by a liquid one will be more advantageous for many CA studies.

Reference: Ming Jin, Raymond Sanedrin, Daniel Frese, Carsten Scheithauer, Thomas Willers; Colloid Polym. Sci. (2016), DOI 10.1007/s00396-015-3823-1

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Mikalai Krutsko, Natallia Yakavets, Olga Opanasenko; The Institute of General and Inorganic Chemistry of the National Academy of Sciences, Minsk, BELARUS

Surface Wetting of Oil Resin-Asphaltene Substances Modified by Surfactants

Colloidal structure of heavy oil dispersible systems is thermodynamically unstable, and the plugging of wells and pipelines occurs as a result of the formation of deposits of the resin-asphaltene substances (RAS). To prevent the loss of stability of heavy oil systems the use of surfactants is promising. Their use contributes to the creating of the optimum conditions of conducting of the engineering processes at various stages of oil production and processing of heavy oil dispersible systems.

In this connection it is important to determine the surface free energy (SFE) of powdery RAS that characterizes the ability of the material to wetting. The RAS isolated from the oxidized bitumen modified of the cationic and nonionic ethoxylated surfactants were used.

To determine the SFE of RAS samples we used the acid-base method. Speeds wetting by test fluids and capillary constants of RAS samples were defined on “Tensiometer K100 MK-2”. Based on the sorption measurements (Washbourn’s method) were determined contact angles and adhesion characteristics (energy of wetting, the adhesion work and spreading coefficient) for wetting of the RAS by liquids with different dispersion, acidic and basic components of the surface tension.

The studies allow us to estimate the effect of surfactants of different chemical nature on the processes of wetting and the magnitude of SFE of oil RAS.

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Masaki Yamaguchi¹, Tetsuhiro Sakata¹, Shunsuke Tamura¹, Kensuke Yokoi²

1) Graduate School of Science & Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, JAPAN

2) School of Engineering, Cardiff University, The Parade, Cardiff CF24 3AA Wales, UK

E-mail: masakiy@shinshu-u.ac.jp

Numerical Studies of Dynamic Droplet Moving for Fluid Analysis

Background: A theory which can enable to estimate the dynamic droplet moving has not been established. We propose a dynamic contact angle model in order to investigate a water droplet moving behavior numerically onto a flat surface.

Methods: The experimental system was consisted from a high speed camera (HX-6, Nac Image Technology, Japan) and a contact angle calculating software using tangent method. Distilled water was used as the sample liquid and the substrate was a silicon wafer whose equivalent contact angle, e, was 62.88. Pictures of 512 72 pixcels at a frame rate of 100 kfps (10 s/frame) were recorded. A characteristic between the dynamic contact angle, (v), and the velocity of triple point, v, was obtained experimentally. A dynamic contact angle model based on experimentally observations was proposed as a dynamic contact angle model as follows:

(v) = min if v 0, = max if v < 0 (1)

where, Ca is the Capillary number, ka and kr are material related consistants for advancing and receding, mda and mdr are maximum and minimum of dynamic contact angle, respectively. The numerical simulation uses the experimentally observed droplet behavior such as initial droplet diameter of 2.048 mm and impact speed of 1.67 m/s.

Results and Discussion: A computational fluid dynamics simulation obtained by solving the Navier-Stokes equation. The calculated results between the dynamic contact angle and the velocity of triple point agreed well with the measured results within 2.8% of errors. In addition, the maximum diameters of moving droplet of the calculated and measured results were 6.40 and 6.54 mm, respectively.

Conclusion: It was considered that precise dynamic contact angle modelling play an important role in the estimation of droplet moving behavior

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