ABSTRACTS


The following is a list of the abstracts for papers which will be presented in SEVENTH 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, Firefox ... etc.)




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INDEX BY AUTHOR

(CLICK ON AUTHOR NAME TO GO TO FULL ABSTRACT)

INDEX BY TITLE

 A. Amirfazli


A New Method for Measuring the Contact Angle of Asymmetric and Symmetric Drops

Alidad Amirfazli

Drop Adhesion to Surfaces Exposed to a Shearing Airflow

Costin Anghel



Contact Angle Measurements for Monitoring Influence of Atmospheric Pressure Plasma on Wood Surfaces

Thomas Bahners

The “Do’s” and “Donts” of Wettability Characterization in Textiles

Edward Bormashenko

Novel Investigations of Liquid Marbles

Laurence Boulangé


Physico Chemical Study of Environment-friendly Emulsifiers for the Road Industry Using Drop Shape Analysis

Miguel A. Rodríguez-Valverde

A New Strategy to Predict the Equilibrium Contact Angle of Rough Homogeneous Surfaces from Contact Angle Hysteresis Measurements

Shreerang S. Chhatre


Girifalco – Good Analysis on Perfluorinated SiOx Surfaces

 Chang-Hwan Choi



Effects of Micro and Nano Particles on Wetting Dynamics of Evaporating Droplets on Superhydrophobic Surfaces

Y.L. Chow



A Study of Grey Cotton Fabric Using Laser Technology and Contact Angle Goniometry

Jules S. Diawara


Forced Wetting of Steels by Liquid Zinc

Yu Fu



Effects of Nano-additives on Dynamic Wetting Behavior and Flowability of Epoxy Resins

A. A. Hamouda


Wettability Alteration of Sand Stone by Nitrogen Based Component and its Effect on the Interfacial Charge Between Asphaltenic Model Oil and Sulfate and Magnesium Ions

Augustin Karasangabo



Investigation of the Nature of Liquid Steel – Alumina Interfacial Interactions from Sessile Drop Measurements: Cases of Fe-ti and Fe-p Alloys

Halim Kusumaatmaja

Wetting on Membranes

Y.L. Lam



Surface Physical and Chemical Analysis of Plasma-treated Cotton Fabric Subjected to Wrinkle-resistant Finishing

L. Mazzola

An Innovative non Contact Method to Measure Surface Free Energy on Micro Areas

Srinivas Mettu


Stochastic Relaxation of the Contact Line of a Water Drop on a Solid Substrate Subjected to White Noise Vibration: Roles of Hysteresis

Adam J. Meuler


Towards Practical Omniphobic Coatings

Masataka Murahara

Plasma Pre-treatment Effect for Photo-chemical Modification and Patterned Functional Group Substitution onto Low Wettable Materials

Niklas Nordgren

Tailored Interfacial Properties by Surface Grafting: From Tunable Biofiber Adhesion to Superhydrophobic Cellulose

Mahesh V. Panchagnula

Equilibrium Shapes of Drops on Hysteretic Surfaces

Kyoo-Chul (Kenneth) Park



Robustness Analysis of Non-Wetting Surfaces Based on Distorted Liquid-Air Interfaces of Droplets

Marko Petrič



Contact Angle Measurements on Wood And Calculation of Its Surface Free Energy

Sonja Richter


Contact Angle Measurements for the Assessment of Corrosion Issues in Carbon Steel Pipelines Carrying Crude Oil.

Jonathan Rothstein


Drag Reduction Using Superhydrophobic Surfaces

M.E.R. Shanahan



Wetting Hysteresis as Induced by Liquid Nano Suspensions

Konrad Terpiłowski


Apparent Surface Free Energy of Ultrafiltration Membranes

Tamir Stein

Electrostatically Driven Droplets Deposited on Superhydrophobic Surfaces

Rafael Tadmor


The Influence of Normal Force on the Lateral Force at the Interface Between a Liquid Drop and a Surface

Peichun Amy Tsai



Wetting Transition, Drop Impact, and Micro-flows upon Hydrophobic Microstructures

Rajneesh Verma

Superhydrophobic Surface of Perfluorocyclobutyl Ethers (PFCBS) Produced Through Electrospinning

Andreas Wego


Photochemical Functionalization of Carbon Fibers for Enhanced Matrix Adhesion

Andreas Wego



Creating Super-hydrophilic Surfaces by Photo-induced Micro-folding

Christophe Ybert




Liquid Dynamics at Superhydrophobic Surfaces: from Friction to Teapot Effect

 

 


S. F. Chini, A. Amirfazli; Department of Mechanical Engineering, University of Alberta, Edmonton, AB, CANADA T6G 2G8


A New Method for Measuring the Contact Angle of Asymmetric and Symmetric Drops


Contact angle measurement is important, as it defines the wetting characteristic of the surface (also the drop adhesion force). In most drop shedding studies, drops are asymmetric. Literature lacks an automated method for measuring the accurate contact angle of asymmetric drops. In this study, an automated method for measuring the contact angle of both symmetric and asymmetric drops, i.e. optimum sub-pixel polynomial fitting (OSPPF), is developed. “OSPPF” is verified using synthetic drops with known contact angles (between 10 and 170 degrees), and good agreements (less than 1 degree error) were obtained. “OSPPF” also, calculates the drop height, wetting width and tilt angle of the camera with respect to the drop base line. “OSPPF” automatically detects the drop boundary, and contact points with sub-pixel resolution. “Canny method” with Otsu's threshold is used to find the drop boundary. Sub-pixel location of the boundary is found using midpoint of the sigmoid of pixel intensity (the midpoint has the highest pixel intensity change). For cases, where contact point is not readily observable or pixelized, a novel algorithm is developed to detect the exact location of the contact points. Use of the median filter (which preserves the drop boundary and removes the noises) along with the Savitzky-Golay filter, makes the OSPPF method robust to a reasonable level of noise (i.e. Gaussian noise with variance of 0.15). Example of application of OSPPF for drops on tilted surfaces as well as horizontal surface will be presented in either sessile or pendant configurations.




Fig. - User interface of the OSPPF is shown.



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Andrew J. B. Milne and Alidad Amirfazli; Department of Mechanical Engineering, University of Alberta, Edmonton, AB, CANADA


a.amirfazli@ualberta.ca


Drop Adhesion to Surfaces Exposed to a Shearing Airflow


In this talk, we use surface science and fluid dynamics principles to explain incipient motion of sessile drops exposed to shearing airflow, with application, e.g. to airfoil icing and fuel cell flooding. Processing high speed video, the variation of contact angles from quiescent (axisymmetric) conditions to incipient motion/runback can be analyzed as the air and drop speed changes. Contact angle is seen to change from quiescent values to values near the advancing and receding when the drop starts to move. The differences between the upstream/downstream and receding/advancing contact angles will be discussed, and how these affect adhesion. By placing the drop on a floating element wall shear sensor an independent measure of the adhesion of the drop can be calculated by monitoring the drag on the drop. Through experiments with water, hexadecane, and PDMS liquids (0.5- 100 ìl) on PMMA, Teflon, and a superhydrophobic aluminum surface (SHS), wetting parameters such as surface tension, drop shape and contact angle are found to be major controllers of both adhesion and drag forces. Exponential functions are proposed to relate necessary air velocity to drop base length and projected area. By normalizing results, systems can be collapsed to a single curve that also explains results from other researchers, vastly increasing predictive power. SHS are seen to shed drops more easily compared to the other surfaces, with some evidence that the drops roll along the surface instead of sliding. Figure 1: Showing a drop on superhydrophobic aluminum under shear flow, with far left image showing undeformed drop in quiescent conditions. Subsequent images show a deformation of the drop and evolution of the contact angles (middle two images), eventually leading to the shedding of the drop (far right image).


Increasing Airflow/Time


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Costin Anghel and Bernard Riedl; Wood Science Department, Laval University, Sainte-Foy, Quebec G1K 7P4, CANADA


Contact Angle Measurements for Monitoring Influence of Atmospheric Pressure Plasma on Wood Surfaces


Plasma treatment has been used over the last few years in order to alter the surface properties of wood. Depending of plasma reactors type and plasma gas, various properties can be improved, such as wood wettability, water repellence and coating adhesion. Atmospheric plasma reactors present the advantage that they could be inserted in a production line at very low cost, allowing the development of a new generation of wood products.


In this study, the effect of several plasmas on sugar maple (Acer saccharum) and black spruce (Epicea mariana) is evaluated by contact angle analysis and coating pull-off tests. According to experimental results, it turns out that the wettability of maple and spruce can be highly influenced by plasma gas and exposure time. Repetition of contact angle measurements after 1 and 2 weeks revealed that the effect of atmospheric plasma on wood surfaces is not permanent. It is important to highlight the effect of normal pressure air plasma on maple, which possibly leads to the development of industrial plasma reactors at atmospheric pressure for wood industry.


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Thomas Bahners; Deutsches Textilforschungszentrum Nord-West e. V.

Institut an der Universität Duisburg-Essen Adlerstraße 1, 47798 Krefeld


The “Do’s” and “Donts” of Wettability Characterization in Textiles


Innovative technologies for surface modification and finishing constitute a key factor to product development and optimization of modern textiles for technical and industrial application. Most surface treatments introduce chemical modifications to the fiber surface that affect the free surface energy. This is done either with the obvious aim to change the wetting behavior with regard to water or oils, or to affect properties that are related to surface energy and wettability, such as, e.g., adhesion phenomena, surface conductivity, adsorption of proteins etc.


On planar substrates, the measurement of the contact angle of specific fluids and making use of formalisms such as, e.g., Neumann or Owen-Wendt equations is a proven method to determine the free surface energy – and, accordingly, often applied to textile substrates. It has to be said, though, that the critical consideration of analytical methods cannot be overemphasized as far as textile substrates are concerned. The geometry of a textile – defined by the topography of the fiber, the construction of the yarn, and the construction of the fabric – is extremely complex. In addition, polymer fibers may be porous and take up water and/or humidity from the environment. Thus, the apparent ‘contact angle’ is the result of simultaneous spreading (on a rough surface), penetration, and capillary motion in the multi-porous system, and – in many cases - can be doubted to provide any information at all.


Given this background, textile researchers make use of various simple to difficult to interpret testing methods ranging from drop penetration tests to modifications of the Wilhelmy-method.


The presented paper is meant to critically discuss to pros and cons of various methods common the textile researcher


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Edward Bormashenko; Ariel University Center of Samaria, Applied Physics Faculty, Ariel, Israel, 40700, P.O.B. 3


E-mail: edward@ariel.ac.il


Novel Investigations of Liquid Marbles


Liquid marbles are non-stick droplets coated with organic or non-organic powder. The nature of contact of liquid marbles with solids and liquids is discussed. Effective surface tension of liquid marbles was measured by three independent experimental techniques: vibration, shape analysis, and maximal marble height. Marbles obtained with various hydrophobic powders: polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, graphite and lycopodium, were studied. The effective surface tension depends strongly on the kind of the powder coating the marble. The capillary interaction between particles coating the marble was involved for qualitative interpretation of the reported data.


Electric properties of "conductive liquid marbles" coated with graphite powder are presented. Formation of marbles coated with hydrophilic powders (graphite) is discussed. Technological applications of "liquid marbles" are proposed, including revealing of water pollution.



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Laurence Boulangé (1), Flora Sterczynski (1, 2)


1) EIFFAGE Travaux Publics, Centre d'Etudes et de Recherches de Corbas, FRANCE

2) CPE Lyon, Villeurbanne, FRANCE


Physico Chemical Study of Environment-friendly Emulsifiers for the Road Industry Using Drop Shape Analysis


Our objective was first to develop new physico chemical methods to characterise the aggregate, the bitumen, and the bitumen emulsion surfaces, to compare the properties of the new sustainable emulsifiers with those currently used in the road industry and finally to explain the role of the aggregate / bitumen interface in the bitumen emulsion breakdown.


It was possible by using a Drop Shape Analysis System to determine the surface tension of complex liquids such as bitumen, surfactant containing aqueous phase and bitumen emulsions. The interfacial phenomena between a bitumen emulsion and an aggregate are driven by the polar and dispersive interactions. Creating a bitumen emulsion can be described by the interfacial thermodynamics where the polar interactions play a major role in the emulsion adhesivity on the aggregate but also in the emulsion breakdown.


Several vegetal emulsifiers can completely fulfil the standard specifications required for the bitumen emulsions in the road industry. As a general rule, using environment friendly emulsifiers decreased by a factor between 3 and 5 the quantity of acid added in the emulsion.


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Javier Montes Ruiz-Cabello, Felipe II Guerrero-Barba, Miguel A. Rodríguez-Valverde, Miguel A. Cabrerizo-Vílchez; Biocolloid and Fluid Physics Group, Department of Applied Physics, University of Granada, SPAIN


A New Strategy to Predict the Equilibrium Contact Angle of Rough Homogeneous Surfaces from Contact Angle Hysteresis Measurements


In adhesion phenomena, wettability of solid surfaces is a controlling parameter. Wettability is usually evaluated by contact angle measurements. Engineered surfaces are very often chemically heterogeneous and rough, thereby several undesired effects are found such as stick-jump-slip behavior, meta-stability... These effects cause a strong variability in experimental contact angles and hide the solid surface energetics. In order to obtain meaningful contact angles, it is recommended to measure the two extreme angles, which delimit the range of contact angle hysteresis. These angles are called advancing and receding contact angles and their values become relatively reproducible using the same experimental method for a given surface. Otherwise, the values of advancing/receding contact angle measured by different interfacial methods usually disagree for a given surface. Regardless of the delicate preparation of solid surfaces, that disagreement reported in literature is not always explained by the experimental uncertainty (e.g. optical resolution) or the measuring conditions (ambient vibration, thermal agitation…).


In this work, the sessile drop and captive bubble methods were compared using textured PDMS surfaces and dematerialized water. The results of contact angle hysteresis were explained by a simplistic theoretical model based on asymmetric sawtooth-like topographies. A new approach was proposed to predict the equilibrium contact angle of rough homogeneous surfaces. This approach was verified with the concerning values of vibration-induced contact angle.


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Wei Xu, Rajesh Leeladhar, and Chang-Hwan Choi; Department of Mechanical Engineering, Stevens Institute of Technology, NJ, USA


Effects of Micro and Nano Particles on Wetting Dynamics of Evaporating Droplets on Superhydrophobic Surfaces


A superhydrophobic surface, characterized as a surface onto which the contact of a liquid droplet exceeds 150̊ with very low contact angle hysteresis, has many engineering applications such as microfluidics and biomedical. Although the wetting dynamics of droplets on the superhydrophobic surfaces had been extensively studied with a variety of micro and nano-patterns in different thermodynamic conditions, most tested liquids were limited to be pure water. However, most microfluidic and biomedical applications deal with liquids containing various micro and nano-sized particles. Thus the systematic understanding of the effect of micro and nano-particles on the droplet wetting dynamics is essential but still lacking. In this paper, we report the wetting dynamics of particle-laden liquid droplets in evaporating on superhydrophobic surfaces with systematically controlled surface parameters and particle compositions. Several wetting phenomena, including evaporation kinetics, wetting transition and dry-out deposition pattern, will be examined and compared with that of pure liquid. The results presented in this paper will enable better understanding of the interfacial wetting phenomena of complex fluids, resulting in significant impact on the design and performance of various microfluidic and biomedical devices and systems using particle-laden droplets.



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Shreerang S. Chhatre, Jesus O. Guardado,* Joseph M. Mabry, § Gareth H. McKinley, and Robert E. Cohen; Massachusetts Institute of Technology, Cambridge, Massachusetts 02139


† Department of Chemical Engineering,

* Department of Materials Science and Engineering,

‡ Department of Mechanical Engineering,

§ Space and Missile Propulsion Division, Air Force Research Laboratory, Edwards Air Force Base, California 93524


Girifalco – Good Analysis on Perfluorinated SiOx Surfaces


Fluorodecyl POSS has one of the lowest solid surface energies (γsv = 10 mN/m) ever reported in the literature. In fluorodecyl POSS, the silsesquioxane cages (T8) are surrounded by eight 1H,1H,2H,2H-heptadecafluorodecyl groups. In an attempt to gain a molecular-level understanding of the surface behavior of Fluorodecyl POSS we synthesized POSS cages with varying length of perfluorinated side groups and certain other SiOx molecules with structures that include rings (Q4) and straight chains (D2). The effect of molecular architecture on wettability was assessed through contact angle measurements on a flat silicon wafer spin-coated with a thin layer of each of these molecules. Their solid surface energies were estimated by Zisman analysis with a set of n-alkanes [from hexadecane (γlv = 27.5 mN/m) to pentane (γlv = 15.5 mN/m)] as probing liquids. These results compared favorably with the Girifalco – Good analysis for a broad range of polar and non-polar liquids. The Lifshitz-Van der waals (dispersive) component of the solid surface energy contact7-abs.gif increased from a cage (T8) to a ring (Q4) and to a straight chain (D2) and also as the perfluorinated chain length decreased for the cage molecules. The fluorodecyl Q4 and D2 molecules had a significantly higher polar component of the surface energy contact7-abs1.gif . Such differences in the solid surface energy can be rationalized on the basis of the difference in the –Si/O– architecture of these molecules.


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Y.L. Chow, C.K. Chan and C.W. Kan; Institute of Textile and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, HONG KONG


E-mail: florence.cyl@gmail.com


A Study of Grey Cotton Fabric Using Laser Technology and Contact Angle Goniometry



In this paper, the surface structure of natural grey cotton fabrics were changed by laser irradiation. The cotton fibres show a characteristics sponge-like morphology after treating with CO2 laser irradiation. The impact on surface morphology of cotton with laser was evaluated using Scanning Electron Microscope (SEM). Apart from this, the wettability of grey cotton fabric treating with laser was examined by contact angle meter. After treating with laser, the values of contact angle of grey cotton fabrics decreased. As for the wetting performance, the laser irradiation is able to cause modification on grey cotton fabric, and thus it is believed that the wetting properties and dyeability of laser treated cotton may also be affected. The dyeing properties of laser treated cotton fabrics were studied. Moreover, the laser irradiation can induced cracks and engraving effect on the fibres. After laser treatment, the breaking strength decreased greatly. The reduction of tensile strength indicated the laser could cause damage on the fibres.


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Jules S. Diawara; Laboratoire de Génie des Procédés et Matériaux, Ecole Centrale Paris, 92290 Châtenay Malabry, Bureau 349, FRANCE


Forced Wetting of Steels by Liquid Zinc


(Abstract not yet available)



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Yu Fu and W. H. Zhong; School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164


Effects of Nano-additives on Dynamic Wetting Behavior and Flowability of Epoxy Resins


The performance of a polymer matrix can exert significant influence over a wide range of properties of the fiber-reinforced polymer composite and is hence critical for manufacturing high-performance fiber reinforced polymer composites for demanding applications in various industries. The addition of nano-additives into polymer resins have shown enhanced mechanical properties, but the processability can be affected negatively due to the increased viscosity from the addition of nano-fillers. Therefore, it is desirable to develop nano-modified resins with enhanced mechanical and thermal properties without degrading the processability. Specifically, improved wetting behavior and excellent adhesion capability are the targets of many researchers. We studied the effects of nano-fillers and combinations of nano-fillers and diluents on the wetting behavior of epoxy resin. To evaluate the effect of the matrix modification on its wettability quantitatively, the measuring techniques of Wilhelmy plate and Du Nouy ring are used to characterize dynamic wetting behavior of the epoxy matrices. The experimental results indicate that the nano-modified epoxy resins, not only possess excellent dynamic wetting performance with an organic reinforcement, but also exhibit extraordinary flowability through reduced viscosity. The resultant nano-modified epoxy resin with reduced viscosity enables energy efficient and environmentally benign resin infusion processing for high quality and high performance FRP composites.


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A. A. Hamouda, University of Stavanger, P. O. Box 8002 Ullandhaug

4068 Stavanger, NORWAY


Wettability Alteration of Sand Stone by Nitrogen Based Component and its Effect on the Interfacial Charge Between Asphaltenic Model Oil and Sulfate and Magnesium Ions


The paper addresses the challenge in wettability alteration of water wet sandstone (SS) to oil wet. The purpose of the wettability alteration is to understand the oil recovery process from asphaltenic oil by different recovery methods at a later stage of this project. A nitrogen based component has been identified to alter the wettability of pure silicate to more oil wet i.e. contact angle above, in this case 100o. The synergy effect between component and asphaltene is demonstrated, where the wettability of the SS to more oil wet. The interfacial charge and interfacila pH of the system in presence of seawater active ions, such as SO4 and Mg, gives an insight into asphaltene behaviour in presence of these ions.


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Augustin Karasangabo and Bernhard Christian ; University of Leoben, Franz-Josef-Straße 18, A- 8700 Leoben, AUSTRIA


Investigation of the Nature of Liquid Steel – Alumina Interfacial Interactions from Sessile Drop Measurements: Cases of Fe-ti and Fe-p Alloys


The wettability of alumina by binary and ternary alloys of the system Fe-Ti-P has been investigated using sessile drop experiments conducted under inert gas atmosphere in the temperature range of 1550 to 1620̊C. The surface and interfacial structures have been explored by scanning electron microscopy and energy dispersive X-ray spectroscopy.

Substantial additions of Ti are known to induce steel melts to wet Al2O3 due to the formation of a Ti rich reaction product at the alloy/ceramic interface, but the present work has shown that even low Ti concentrations can induce a reactive wetting process leading to an improvement of the wettability of Al2O3 by Fe alloys.


The contact angle of molten steel containing P on Al2O3 decreased with increasing P content. The improvement of the wetting behaviour in this system was attributed solely to the adsorption of P on the Al2O3 side of the interface without formation of a reaction product layer. The addition of P as a ternary alloying element to the system Fe-Ti proved to be beneficial to the wetting behaviour. The measured contact angles were much lower than those in the binary systems Fe-Ti and Fe-P.


According to experimental observations, it turns out that the wettability of liquid Fe-based alloys, when an Al2O3 surface is present is not only a function of the metal/oxide couple but is also dependent on the oxygen partial pressure, whereas temperature variations bring about a comparatively small effect.


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Halim Kusumaatmaja, Y. Li, R. Dimova and R. Lipowsky; MPI of Colloids and Interfaces, Am Muhlenberg 2, D-14476 Golm/Potsdam, GERMANY


Wetting on Membranes


Biomimetic membranes exposed to several aqueous phases are studied both theoretically and experimentally. Specific examples are provided by lipid vesicles and phase separating polymer solutions. The theory reveals the existence of an intrinsic contact angle between the membranes and the aqueous phases, reminiscent of the Young’s angle in the usual wetting geometry. An explicit relation is derived by which this intrinsic angle can be determined from the effective contact angles as measured by optical microscopy. A detailed comparison between theory and experiment provides strong evidence that the intrinsic contact angle represents a material parameter, in contrast to the effective contact angles. The theory is then used to describe the protrusion (budding) of one of the phases from the vesicle body.


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Y.L. Lam, C.W. Kan, C.W.M. Yuen and C.H. Chui; Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, CHINA


Tel: (852) 2766 6531 ; Fax: (852) 2773 1432

Email: 07901799r@polyu.edu.hk


Surface Physical and Chemical Analysis of Plasma-treated Cotton Fabric Subjected to Wrinkle-resistant Finishing


In this investigation, the cotton fabrics were treated with oxygen plasma gas and/or wrinkle-resistant finishing agent with polycarboxylic acid. The results of wicking rate, contact angle and wettability tests revealed that the atmospheric plasma treatment significantly improve the hydrophilicity of the cotton fiber. Such improvement greatly enhances the effectiveness of post-finishing processes. Surface morphology of cotton specimens has been investigated to evidence the changes and the presence of metal oxide on the fibre surface. Study also showed that chemical composition of cotton fabric surface varied upon plasma and wrinkle-resistant treatment. The surface chemical composition of the treated cotton specimens were evaluated with different characterization methods, namely FTIR-ATR, and EDX. The experimental results were thoroughly discussed.


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L. Mazzola, M. Sebastiani, E. Bemporad and F. Carassiti; Mechanical and Industrial Engineering Department, University “Roma Tre”, Rome, Italy


E-mail address: luca.mazzola@stm.uniroma3.it


An Innovative non Contact Method to Measure Surface Free Energy on Micro Areas


Surface Free Energy (SFE) is a property quite difficult to measure but very important for the influence that it has on patterned materials concerned in the microelectronics, aerospace or biomedical technologies.

Today contact angle method measure the global mean value of SFE on areas of mm2 size. It is not possible with this method to evaluate deeply the effects of roughness, surface defects, chemical contaminations.

Nanoindentation and Atomic Force Microscopy techniques provide an alternative direct measurement method of the SFE on the small areas (μm2 or nm2) through a contact mechanism triggered by the contact of two bodies. In order to evaluate the adhesion properties, two models Johnson-Kendal-Roberts and Maugis-Dugdale use the pull-off force for the extraction of the indenter tip from the sample. The main limitation of this approach is that the measurements involve the loss of the original surface morphology. In fact the adhesion value obtained refers to the energy balance between two conformal surfaces depending mainly from the morphology of the harder material (i.e. diamond tip).

In this work is described an innovative methodology for the SFE measurement using nanoindenter device. During the tests, the nanoindenter tip was attract to the sample surface until there was a contact. The SFE value is evaluated using experimental force of attraction and displacement of the nanoindenter spherical tip when it approaches the sample surface.

By this method the sample surface is not altered by the tip, therefore respect to pull-off force method, it could be very useful to evaluate SFE considering the morphology of the sample (controlled roughness or pattern).


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Srinivas Mettu and Manoj K. Chaudhury; Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015


Stochastic Relaxation of the Contact Line of a Water Drop on a Solid Substrate Subjected to White Noise Vibration: Roles of Hysteresis


We study the relaxation of three phase contact line of a sessile drop of water on a low energy surface from non equilibrium state to equilibrium state. The external force required to drive contact line to equilibrium state is supplied to drop by subjecting it to a white noise vibration. In non equilibrium state, contact line of sessile drop is acted upon by restoring spring force due to surface tension of liquid as well as resistive force due to contact angle hysteresis. Drop remains pinned at a metastable state when spring force is not sufficient enough to restore contact line to the equilibrium state. With an appropriate amount of external vibration, drop reaches a global equilibrium state. Present study elucidates the dynamics of relaxation analyzed using a modified Langevin equation. The relaxation time of contact line obtained in experiments is higher than the Langevin relaxation time. The measured fluctuation of the displacement of the contact line is highly non-Gaussian as opposed to Gaussian when hysteresis is completely eliminated. It is also shown that an exponential distribution of the displacement fluctuation arises due to the non-linear hysteresis term in the Langevin equation. The large time of relaxation and the anomalous displacement fluctuation suggest that hysteresis is present during the relaxation process of the drop even though the final state reached by the drop is free of hysteresis. We also compare the displacement fluctuations of the contact line on two different surfaces: a silicone rubber and a fluorocarbon monolayer to demonstrate that fluctuation of displacement may be used as a tool to study the surface properties of low energy substrates.


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Adam J. Meuler, Kyoo-Chul (Kenneth) Park, Joseph M. Mabry, Gareth H. McKinley, and Robert E. Cohen


Towards Practical Omniphobic Coatings


Super liquid-repellent surfaces have piqued the interest of many commercial and academic researchers over the past decade. Generally these surfaces have a texture that resists penetration of the liquid into the substrate topography, meaning droplets sit on a composite (solid-liquid-air) interface and are often characterized by a high apparent contact angle and low contact angle hysteresis. Unfortunately many of the surfaces described in the literature are of limited utility in applications due to poor mechanical properties, optical opacity, expensive fabrication procedures, and/or non-robust repellency against low surface tension liquids (e.g., oils). Here we describe the development of a replica molding process to prepare crosslinked fluoroelastomer substrates with submicron re-entrant surface texture. Essential steps in this protocol include the preparation of a master mold using photolithographic techniques, filling the mold and subsequently curing crosslinkable oligomers, and releasing the fluoroelastomer from the template. These optically transparent, mechanically flexible substrates may be characterized by a robust liquid repellency and could find utility as coatings on, for example, touchscreens or optics and electronics equipment.


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Masataka Murahara; Professor Emeritus of Tokai University, JAPAN


Plasma Pre-treatment Effect for Photo-chemical Modification and Patterned Functional Group Substitution onto Low Wettable Materials


here is a method to form microscopic roughness on the surface of a sample in order for a film or adhesive hard to peel off, but it is unsuitable to material surfaces. Thus, the undamaged surface was demonstrated by chemically substituting the functional groups that a coating agent or adhesive had on various materials. A few thin films were successfully deposited, but many were not depending on the kinds of materials and came off if wiped. Then, hydrophilic groups (-OH) were substituted on a sample surface beforehand, and photo-adhesion or coating was carried out. The sample surface was firstly treated by discharge plasma for promoting efficiency of hydroxyl group substitution, and hydroxyl groups were substituted on the sample surface by photochemical reaction of the modification surface and water when the material presented high wettability temporarily; as a result, the interface of adhesion or coating was united persistently.


The contact angle with water of silicone film is 111 degrees; those of PC, PP, PE, fused silica, and sapphire are 101, 90, 95, 40, and 72 degrees, respectively. When those surfaces were irradiated by glow discharge plasma of DC 2 pole sputtering system for 5 minutes, the contact angles of all the surfaces dropped to 5-30 degrees. The contact angles, however, returned to the originals as soon as the water applied to the treated surfaces evaporated. After plasma treatment, a single shot of the patterned ArF excimer laser beam (10 mJ/cm2, 10ns) was irradiated on each pretreated sample surface. In the case of silicone film, the contact angle with water became lower to 6 degrees after the five-minute plasma treatment. Water was applied to the treated surface; which was irradiated with the patterned ArF laser beam at one shot. A hydrophilic property was generated on the part exposed corresponding to the pattern from this result, and the contact angle with water was maintained at 50 degrees for one month; however, on the part unexposed, the contact angle with water returned to the original degree.


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Niklas Nordgren Linn Carlsson, Daniel Nyström, Hanna Lönnberg, Josefina Lindqvist, Emma Östmark, Per Antoni, Camilla Nilsson, Anna Carlmark, Linda Fogelström, Anders Hult, Mats Johansson, Mark W. Rutland and Eva Malmström; Department of Fibre and Polymer Technology, Coating Technology, KTH Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, SWEDEN


Tailored Interfacial Properties by Surface Grafting: From Tunable Biofiber Adhesion to Superhydrophobic Cellulose


The increasing drive to use sustainable resources, like cellulose fibers, in composite applications where previously synthetic materials have been used, has led to issues concerning interfacial compatibility. Moreover, there is a growing need to integrate novel properties and functionality into traditional cellulose based products, such as paper and textiles. The direct grafting of polymer architectures from bio-fibers allows for surface properties to be tailored extending the range of possible applications of these materials.


In this work, surface initiated atom transfer radical polymerisation (ATRP) has been used to render cellulose surfaces superhydrophobic or dual-responsive by varying the architecture and monomer composition of the grafts. Interestingly, branched graft-on-graft structures of long alkyl chains display surface self-cleaning properties similar to that previously seen using environmentally detrimental fluorinated compounds.


Biopolymer grafts have also proven to act as efficient compatibilizers between filler and matrix in cellulose based composites. A recent study using atomic force microscopy (AFM) in colloidal probe mode shows the adhesion between grafted cellulose microspheres to be promoted by chain entanglements in a dynamic manner. Results further indicate that the adhesion and the interfacial toughness can be tuned by varying the length of the graft.


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Bharadwaj R. Prabhala1, Mahesh V. Panchagnula1, and Srikanth Vedantam2


1) Department of Mechanical Engg., Tennessee Technological University, Cookeville, TN 38501, USA


2) Department of Engineering Design, Indian Institute of Technology Madras, Chennai, TN 600036, INDIA


Equilibrium Shapes of Drops on Hysteretic Surfaces


We study equilibrium three dimensional shapes of drops on hysteretic surfaces. We develop a modification to the publicly available surface energy minimization code Surface Evolver to handle contact angle hysteresis. We achieve this by incorporating a mobility relation for the triple line into the Evolver simulations. We demonstrate this model's versatility by studying three problems in which parts of triple line advance while other parts either recede or remain stationary. The first problem, as shown in Figure 1, focuses on the shape of a pendant drop on a vertical hysteretic surface whose volume is increased till impending sliding motion is observed. In the second problem as shown in Figure 2, we examine the equilibrium shapes of coalescing sessile drops on hysteretic surfaces. Finally, we study coalescing puddles in which gravity plays a leading role in determining the equilibrium puddle shape alongside hysteresis


contact7-abs2.gif  

contact7-abs3.gif  

Figure 1: Pendant drop on a vertical surface

Figure 2: Drop coalescence on a hysteretic surface.



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Saurabh Mittra1 and Robert E. Baier2


1) CPF (Pepsi) & NEHF (Lipton) Inc, 25 Copeland Drive, Ayer, MA 01432


2) Department of Mechanical and Aerospace Engineering, Industry/University Cooperative Research Center for Biosurfaces, State University of New York at Buffalo, NY 14214


Infrared Microscopic Monitoring of Microfouling on Germanium Surfaces


Microfouling appears at all solid interfaces with biological fluids, depositing biofilms on a submicrometer protein-dominated “conditioning” film with secondary particulate matter—usually bacteria— growing to micrometer and thicker layers. Disadvantageous effects of microfouling range from heat transfer retardation in pasteurization of dairy products and blocking of cooling lines in beverage manufacture to masking of optical sensors and clogging of microfluidic biosensor circuits. Since heat transfer can be monitored by infrared techniques, and infrared-transparent semiconductors—especially germanium—are widely employed platforms for emerging biosensor and microfluidic lab-on-a-chip devices, this investigation employed noninvasive monitoring of microfouling processes by infrared microscopy through germanium prisms already optimized for multiple attenuated internal reflection infrared spectroscopy of thin-film deposits. The results showed closed-cell surface planar resolution of about 50 micrometers, and depth resolution of 0.5 micrometer, allowing interior “conditioning” film formation to be noninvasively monitored and discriminated from consolidated biofilm, polymer film, and mineral deposits based on both radiance vs temperature plots and thermal images, compared with pre-deposited fibrinogen and hyaluronic acid control film baselines. Infrared microscopy will have a useful role in noninvasive monitoring of induction-period and microfouling events in semiconductor-based biosensors and microfluidic circuits of the future, as well as allow remote, non-contact recording of heat transfer efficiencies in biofilm-limited food processing and bio-pharmaceutical manufacturing operations.



Kyoo-Chul (Kenneth) Park, Shreerang S. Chhatre, Wonjae Choi, Robert E. Cohen, and Gareth H. McKinley


Robustness Analysis of Non-Wetting Surfaces Based on Distorted Liquid-Air Interfaces of Droplets


Liquid droplets in the Cassie-Baxter state form liquid-air interfaces that are not flat but distorted due to pressure differences across the interfaces. These distorted interfaces play an essential role in the transition from the composite Cassie-Baxter state to the fully-wetted Wenzel state and in the determination of the robustness of the composite state. However, there are few studies that consider the details of the distorted interfaces for a wide range of liquids and there is a lack of an a priori method to evaluate the robustness of three-dimensionally complicated textures. We have investigated the shape of distorted liquid-air interfaces and their transition conditions experimentally by using droplets of various low surface tension liquids on millimeter-sized re-entrant surface textures. The experiment results are in good agreement with our newly-developed finite element simulations. These three-dimensional simulations of the interfacial shape provide a predictive tool for the robustness of a wide range of proposed microtextures in terms of the breakthrough pressure at which the distorted liquid-air interface collapses and the droplet transitions to the Wenzel state.



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Marko Petrič and Milan Šernek; University of Ljubljana, Biotechnical Faculty, Department of Wood Science & Technology, amnikarjeva 101, SI-1000 Ljubljana, SLOVENIA


marko.petric@bf.uni-lj.si


Contact Angle Measurements on Wood And Calculation of Its Surface Free Energy


Surface properties of wood are important for its bonding and finishing abilities. In addition, many novel procedures have appeared to overcome less favourite properties of wood (e.g. dimensional instability or susceptibility to weathering), like modification and plasma treatments. Consequently, extensive work has been performed in the past to study wetting phenomena of wood and its surface energetics. Contact angles on wood’s surfaces depend on numerous features like for instance wood species, shares of early and late wood, low molecular weight extractives that migrated to a surface, previous history of a surface, surface roughness, moisture content, porosity, etc. This complexity causes ambiguity on obtained contact angle and surface energy data, since the surface energy calculations assume thermodynamic equilibrium.


Various contact angle measurement techniques regarding wood have been reported and several approaches for surface free energy calculations have been applied. The result is that for the same wood species the reported data on contact angles and surface energies substantially differ.

The aim of this paper, based on extensive review of available literature data, is to systematically describe problems and data on contact angle measurement techniques, wetting of wood and its surface energies. The presented state of the art on wood wettability and surface energy studies may contribute to more certain interpretations of the obtained data in the future.


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Sonja Richter1, Chong Li2, Francois Ayello3, Xuanping Tang1, Win Robbins1, Srdjan Nesic1

 

1) Institute for Corrosion and Multiphase Technology, Department of Chemical Engineering, Ohio University, Athens, OH 45701, USA

 

2) ExxonMobil Upstream Research Company, PO Box 2189 Houston TX, 77252, USA

 

3) Det Norske Veritas, 5777 Frantz Rd., Dublin, OH, 43017, USA

 

Contact Angle Measurements for the Assessment of Corrosion Issues in Carbon Steel Pipelines Carrying Crude Oil.

 

Carbon steel pipelines are used in the oil and gas industry for the transportation of crude oil. Commonly, there is water in the feed and if it flows at the bottom, it can cause corrosion problems, but if it is entrained in the oil phase, corrosion problems will not occur. Furthermore, the crude oil contains surface active chemicals, both added chemicals (such as corrosion inhibitor) or naturally occurring, which can both inhibit the corrosion, and change the wettability of the steel surface, and thus preventing free flowing water from wetting the pipe wall. The ability of the chemicals to alter the wettability of the steel surface is estimated by measuring the contact angle of the oil-in-water and water-in-oil, as well as the oil-water interfacial tension. The in-situ wettability, at various flow rates, is estimated by measuring the conductance at the pipe surface with conductance pins, a method developed for this specific purpose. The conductance pins can be applied to both small-scale benchtop equipment as well as large-scale flow loop equipment. There was a good correlation between increased wettability as shown by contact angles and the in-situ measurements.

 

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Jonathan Rothstein; Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA 01003

 

Drag Reduction Using Superhydrophobic Surfaces

 

A series of experiments and direct numerical simulations (DNS) will be presented which demonstrate significant drag reduction for both laminar and turbulent flows of water through channels using superhydrophobic surfaces with well-defined micron-sized surface roughness. The surfaces are fabricated from PDMS to incorporate precise patterns of ridges or posts that can support a shear-free air-water interface. A flow cell is used to measure the pressure drop and velocity profile as a function of the flow rate for a series of channel geometries and superhydrophobic surface designs. DNS are performed for flow past superhydrophobic surfaces which both complement and extend the range of geometries and Reynolds number obtained in the experiments. We will show that drag reductions up to 75% and slip lengths up to 150mm can be obtained in turbulent flows past superhydrophobic surfaces. Additionally, we will show that slip along the air water interface forestalls the transition from laminar to turbulent flow. The drag reduction is found to increases with increasing post/ridge spacing and the fraction of air-water interface. In turbulent flows, the drag reduction increases with Reynolds number before eventually reaching a plateau. These results suggest that in turbulent flows, the drag reduction scales with the thickness of the viscous sublayer and not the overall channel height as in laminar flows.

 

 

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J. R. Moffat, K. Sefiane and M. E. R. Shanahan; Laboratoire de Mécanique Physique (LMP)-UMR CNRS 5469, Université Bordeaux 1, 351 Cours de la Libération, 33405 TALENCE Cedex, FRANCE

 

Wetting Hysteresis as Induced by Liquid Nano Suspensions

 

(Abstract not yet available)

 

 

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Tamir Stein; Ariel University Center of Samaria, Department of Chemical Engineering and Materials. Bar-Ilan University, Chemistry Department.

 

Electrostatically Driven Droplets Deposited on Superhydrophobic Surfaces

 

Rapid progress in the field of microfluidics inspired intensive research in the field of actuation of liquid droplets. Microfluidic devices demonstrated potential for diverse applications as DNA microarrays, drug screening, optical displays etc. Droplets could be actuated by different factors including surface stresses, external field and other. Electrostatically displaced and levitated drops were reported lately. Our letter is focused on the electrostatic actuation of sessile drops, which can serve as an alternative to electrowetting control of the shape of sessile drops.

The reported method is a non-contact one; this may be an important advantage for optical applications. On the other hand it demands relatively high fields which are undesirable in a view of safe handling of engineering devices. In the future this electrostatic actuation of sessile drop may be can serve as a method of pinning force measurements on superhydrophobic surfaces, and as alternative method to measure surface tension of liquids.

 

tsteinimg.jpgSchematic illustration: Electrostatic actuation of a water droplet. Solid line corresponds to the initial drop state; dashed line describes the maximal drop deformation.

1.     Ch-M. Ho, Yu-Ch. Tai, Annu. Rev. Fluid Mech. 30, 579 (1998).

2.     S. Chandrasekhar and E. Fermi, Astrophys. J. 118, 113 (1953).

3.E. Bormashenko, T. Stein, G. Whyman, Y. Bormashenko, and R. Pogreb. Langmuir 22, 9982–9985 (2006).

 

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Rafael Tadmor, Prashant Bahadur, Aisha Leh, Hartmann E. N'guessan, Rajiv Jaini, Lan Dang and Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont TX 77710

 

The Influence of Normal Force on the Lateral Force at the Interface Between a Liquid Drop and a Surface

 

A novel instrument allows for the first time measurements of the lateral adhesion forces at a solid-liquid interface, f||, in a way that is decoupled from the normal forces, f^. We use it to measure how f|| between a drop and a surface is influenced by different f^ and different histories of drop resting periods on the surface prior to sliding, trest. The variation of f|| with trest is similar for different f^ and always plateaus as trest →¥. We show that the f|| plateau value is higher when f^ is lower. This seemingly counter intuitive result is in agreement with recent theories

 

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Peichun Amy Tsai1, Christophe Pirat1, Detlef Lohse1, Alisia M. Peters2 , Rob Lammertink2, Matthias Wessling2, Sergio Pacheco3 and Leon Lefferts3

 

1) Physics of Fluids Group, University of Twente, THE NETHERLANDS

2) Membrane Technology Group, University of Twente, THE NETHERLANDS

3) Catalyst Materials and Process Group, University of Twente, THE NETHERLANDS

 

Wetting Transition, Drop Impact, and Micro-flows upon Hydrophobic Microstructures

 

Hydrophobic microstructures, displaying superhydrophobicity, are both intriguing and offer perspectives for microfluidic applications. In this talk, three examples of wetting effects on regular and unregular water-repelling surfaces are presented, namely:

 

(i) An evaporation-triggered wetting transition at which a gently deposited water drop on the microstructures jumps from the Cassie-Baxter- to the Wenzel-wetting state

 

(ii) A drop impact on superhydrophobic substrates, with an emphasis of the influences of nano-roughness and air pressure, and

 

(iii) Laminar micro-flows over hydrophobic micro-grooves, with which effective slippage can be achieved.

 

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Rajneesh Verma, Neetu Tomar and Dennis W. Smith, Jr.*; Department of Chemistry, Clemson University, Clemson, SC-29634

 

* Corresponding author; E-mail: dwsmith@clemson.edu

 

Superhydrophobic Surface of Perfluorocyclobutyl Ethers (PFCBS) Produced Through Electrospinning

 

Semi fluorinated polymer especially perfluorocyclobutyl (PFCB) aryl ether polymers are in high demand in the industries due to their versatile nature such as high thermal resistance, chemical resistance and tunable refractive index to name a few. They are prepared by radical mediated [ 2+2 ] thermal cyclo dimerization of Triflourovinylether (TFVE) monomers (Scheme 1)1

rvermafig.jpg

 

 

 

 

 

 

 

 

 

 

 

 

Scheme.1 Radical mediated [ 2+2 ] thermal cyclo dimerization of TFVE monomers

 

The biphenylperfluorocyclobutyl (BP-PFCB) polymers known to generate hydrophobic surfaces due to their low surface energies.2 Superhydrophobic surfaces are generated by simple one step method of electrospinning of BP-PFCB polymer. The hydrophobicity and superhydrophobicity can be changed by changing the surfaces morphology, which inturn can be controlled by changing electrospinning conditions. Superhydrophobicity of the BP-PFCB polymer (Contact angle> 150º) was achieved by varying various electrospinning parameters such as flow rate, voltage, distance and concentration.

 

References:

1.Babb, D.A. Fluoropolymers: Synthesis; Plenum Press: New York, 1999, pp 25-50.

2 .Iacono, S. T.; Ligon, Jr., C.S.; Vij, A. Mabry, J. M.; Smith, D. W., Jr. Poly Prepr, 2005, 46 (2), 640

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Konrad Terpiłowski1, Małgorzata Bielska2, Krystyna Prochaska2, Emil Chibowski2

 

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

 

2) Institute of Chemical Technology and Engineering, Poznan University of Technology, Poznan, POLAND

 

Apparent Surface Free Energy of Ultrafiltration Membranes

 

The hydrophobic properties of three polymeric membranes for utrafiltration (Cellulose acetate CA, Polysulfone PS, Polyvinylidene fluoride PVDF) were determined by advancing and receding contact angle measurements and then the values of free surface energy were estimated. The contact angles were measured by sessile drop method for water, surfactant solutions (Sodium dodecylsulfate SDS, hexadecyltrimethylammonium bromide CTAB, oxyethylated coconut fatty acid methyl esters OMC), and binary mixtures of each ionic with the non-ionic surfactants. The apparent surface free energy was calculated using hysteresis approach [1] and Neumann equation of state [2]. Using Tadmor’s [3] approach the equilibrium contact angles were also evaluated. The obtained results enabled to conclude about hydrophobicity of the ultrafiltration membranes.

 

 

ACKNOWLEDGEMENT

We acknowledge the financial support from Polish Ministry of Higher Education and Science, Project No. N204 130 435 and DS-32/067/2010.

 

REFERENCES

 

[1] E. Chibowski, Adv. Colloid Interface Sci., 103, 149 (2003).

[2] A.W. Neumann, R.J. Good, C.J. Hope, M. Sejpol, J. Colloid Interface Sci. 49, 291 (1974).

[3] R. Tadmor, Langmuir, 20, 7659, 2004

 

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Andreas Wego1, Lutz Prager2 and Thomas Bahners1

 

1) Deutsches Textilforschungszentrum Nord-West e.V., Adlerstr. 1, 47798 Krefeld, GERMANY

email: info@dtnw.de

 

2) Leibniz-Institut für Oberflächenmodifizierung e.V., Permoserstr. 15, 04318 Leipzig, GERMANY

Email: lutz.prager@iom-leipzig.de

 

Creating Super-hydrophilic Surfaces by Photo-induced Micro-folding

 

Highly hydrophobic finishes find increasing interest for a wide range of technical surfaces, especially under the assumption of improving cleanability or even creating self-cleaning properties. In recent years, however, the opposing nature of a surface, i.e. super-hydrophilicity, was found to lead to similar or even better properties with regard to dirt take-up, cleanability and self-acting cleaning effects. A common technique in this context is to employ photo-catalytic anatas, which under UV irradiation yields extremely low water contact angles and, at the same time, radicalic decomposition of organic debris. The approach has found application in the finishing of roof tiles, car windows and coated textiles, to name but a few.

 

The general description of roughness-dependent wetting by, e.g., Wenzel’s equation indicates, however, that extreme wetting is also achievable without the integration of photo-catalytic TiO2, which, if integrated in organic coatings applied to textiles, is aggressive to coating and textile as well.

 

The aim of the presented work, therefore, was to study the wetting behavior of micro-structured organic coatings, as technically applied to technical textiles as, e.g. tarpaulins or textile roofs. In this work, the micro-roughness is achieved by a two-step curing process of acrylates where UV irradiation with λ < 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.

 

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Christophe Ybert; LPMCN, Batiment Brillouin, Université Lyon 1, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, FRANCE

 

 

Liquid Dynamics at Superhydrophobic Surfaces: from Friction to Teapot Effect

 

 

The possibility to affect liquid flows through surface properties was naturally put forward by the recent emergence of small-scales fluidic devices, as downsizing invariably emphasizes the role of surfaces, with respect to bulk properties. Such strategy of flow modification by surface effects is a priori restricted to the natural scales setting the interactions between the surface and the nearby liquid that is, essentially to nanometric scales. In this context, superhydrophobic surfaces have emerged as possessing not only remarkable (non-)wetting properties but also unique dynamical properties.

 

Starting with liquid-solid friction properties, I will first discuss how such surfaces can enhance surface slippage by orders of magnitudes compared to conventional smooth surfaces. More importantly, I will show how such performances quantitatively relate to the very details of the superhydrophobic surface structure (topology, length scale, etc.) rather than on the mere wettability parameter.

 

In a second step, I will then show that the impact of superhydrophobic surfaces on fluid dynamics extends significantly beyond the previous frictional properties. As an illustration, I will discuss how they allow revisiting some large scale, inertia-dominated, flows as encountered in splashing or in the flow separation and trickling phenomena (the so-called teapot effect). In these macroscopic situations too, for which surface effects have been usually ignored in view of the large Weber numbers involved, superhydrophobic surfaces will prove to have a dramatic influence.

 

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