ABSTRACTS

The following is a list of the abstracts for papers which will be presented in SIXTH 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.)

The Reciprocal Relationship Between Donor-acceptor and Dispersion Forces

Confounding factors inherent in several methods in the literature for reducing contact angles to solid surface energies and their dispersion and donor-acceptor components are discussed. A new perspective is obtained from a review of the experimental and theoretical studies of the unique structures and properties found in the molecular zone of liquid adjacent to solid surfaces. Taking this zone into account, a reciprocal relationship is found between the dispersion and donor-acceptor components of interfacial interactions between polar liquids and polar solids. On this basis, a simple empirical method is developed to separate the work of adhesion into a dispersion and donor-acceptor component. Consistent validation is obtained from contact angle data on a series of end-functionalized self-assembled monolayers, as well as two series of polymers. Also it is shown that these interactions all show amphoteric character.

Reversible Transition from Hydrophobicity to Hydrophilicity of Photon Responsive Surfaces: From Photochromic Molecules to Nanocrystals

The presented work deals with the exclusive use of light to change reversibly the wettability of surfaces. This fascinating property is due to the involvement of photoresponsive materials. Two categories of materials are investigated: organic photochromic molecules, and inorganic colloidal nanocrystals. In the case of the photochromic molecules, the wetting characteristics of surfaces of polymers doped with such molecules can be tuned when irradiated with laser beams of properly chosen photon energy. Their hydrophilicity is enhanced upon UV laser irradiation, and the process is reversed upon green laser irradiation. The mechanism involved in these transformations is the photoinduced isomerization between the isomeric forms of the photochromic molecules that have different polarities. Structuring of the photochromic polymeric surfaces enhances significantly both the initial hydrophobicity of the system and the light-induced wettability variations of the surfaces. In the case of the inorganic nanocrystals we examine different substrates coated with organic-capped TiO2 nanorods. Such nanorod-based coatings exhibit a surface transition from a highly hydrophobic state to a highly hydrophilic one under selective UV-laser irradiation. This behaviour is reversed under long dark storage. The mechanism involved is a progressive increase in the degree of surface hydroxylation of TiO2 upon UV irradiation. The surfactant molecules that cover the NRs appear to undergo simultaneous conformational changes without suffering any significant photocatalytic degradation.

1) Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY; Email: info@dtnw.de

2) Technische Universität Dresden, Institut für Textil- und Bekleidungstechnik, Mommsenstraße 13, 01062 Dresden, GERMANY

itb@tu-dresden.de

3) Leibniz-Institut für Polymerforschung e.V., Hohe Straße 6, 01069 Dresden, GERMANY; Email: ipf@ipfdd.de

The Effect of a Plasma Pre-treatment on the Quality of Flock Coatings on Polymer Substrates

Flock coating is a widely used process to create a textile-like texture on substrates of arbitrary shape and material. In the process, flock fibers - short fibers typically 1 to 3 mm long - are oriented and accelerated towards the substrate by means of an electric field. Impacting fibers are stuck to the substrate surface by an appropriate adhesive. The technique is applied to products as diverse as textiles, plastic car interior components, floor coverings or furniture with the objectives being decorative, but also functional effects, e.g., with regard to friction. Substrate materials range from polymers to metal as well as ceramics.

Primary quality criteria are adhesion of the flock fibers, but also the so-called flock density, i.e. number of fibers per unit area, and evenness. Here, influential physical and chemical factors refer to interfacial adhesion, but also charging effects by the impacting fibers. Up to now, these aspects have been addressed by choice of adhesive as well as fiber polymer and process parameters.

Present developments, especially with regard to car parts, aim at easy to recycle single-material systems, i.e. substrate, adhesive and flock fibers based on identical polymer chemistry. A system presently under investigation is comprised of a molded car component, hot-melt adhesive, and flock fiber based on aliphatic polyamides. One aspect in this study was the application of an air plasma pre-treatment of the PA substrate, mainly in order to increase hot-melt adhesion. The presented paper will give a general overview over physical and chemical properties of the treated surfaces and the resulting effects on flock coating.

Contact Angle Hysteresis on the Polymer Substrates: Experimental Techniques and Calculation of CAH Energy

Advancing and receding contact angles were measured on the various polymer substrates, namely: polyethylene, (PE), polypropylene (PP), polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) poled and non-poled. Various experimental techniques applied for contact angle hysteresis (CAH) measurement were compared. New experimental technique intended for CAH measurement is presented. Advanced angles established on different substrates with various experimental techniques were close, whereas receding angles differed significantly. The sensitivity of the receding contact angle to the experimental technique is related to behavior of the precursor film surrounding the water drop deposited on the polymer substrate. The fine structure of the triple line and the precursor film were studied with environmental scanning electron (ESEM) microscopy. New approach to calculation of CAH energy is proposed. The various existing approaches to the evaluation of the contact angle hysteresis energy are discussed.

Study of the Cassie-Wenzel Wetting Transition Using Vibrated Drops

The transition between the Cassie and Wenzel wetting regimes has been observed under vertical and horizontal vibrations of the water drop placed on the rough patterns. Vertical vibrations of the drop at the frequencies which are far from resonance were studied. In this case the wetting transition takes place under a constant force per unit length of the triple contact line as observed for various rough surfaces.

When the vibrations are horizontal the observed wetting transition is of a distinct resonance character. The resonance frequencies as established experimentally coincide with the calculated eigenfrequencies of capillary-gravity standing waves on the drop surface. The resonance Cassie-Wenzel transition is related to the displacement of the triple line caused by both the inertia force and the increase in the Laplace pressure. This strengthens the idea that Cassie-Wenzel wetting transition is more likely 1D affair stipulated by the triple line behavior. The study of the vibrated drop deposited on the rough surface supplied valuable information concerning the Cassie-Wenzel wetting transition.

Effect of the Surface Solid Heterogeneity on Protein Stabilization

Hydrophobic surfaces in prefillable syringes are known to mediate protein denaturation. A model of insulin aggregation upon exposure to glass beads has been reported. This model consists of monomer denaturation due to conformational changes. Those changes correspond to exposure to aqueous solution of the internal hydrophobic moieties leading to reversible adsorption at hydrophobic surface followed by stable intermediates which facilitate macroaggregation.

The aim of the current work was to evaluate effects of a composite surface of polysiloxane that can cause supramolecular organization of therapeutic protein in prefillable syringes. An innovative methodology of surface characterization was developed coupling dynamic water contact angle (WCA), Environmental Scanning Electron Microscopy (ESEM) and XPS analysis on genuine non planar surfaces.

A stability study with human insulin was conducted in polysiloxane coated prefillable syringes. The protein aggregation was then measured after 14 days of stabilization using DLS (Dynamic Light Scattering). There was no general trend describing the protein stability measured by DLS after contact with functionalized glass.

A first tentative model based on the Cassie Baxter equation was proposed in this paper where chemical heterogeneity of polysiloxane surface can explain the equilibrium kinetics between native forms of insulin and stable intermediates. This study contributes to improving the knowledge of the complex protein / container closer interactions and to the development of a new generation of prefillable syringes.

1) Departament of Applied Physics, Faculty of Sciences, University of Granada, E-18071 Granada SPAIN

2) GKSS Research Center Geesthacht GmbH, Institute of Chemistry, Kantstrasse 55, D-14513 Teltow GERMANY

Model For Estimation of The Young Contact Angle From Contact Angle Hysteresis Measurements

A solid surface is usually characterized, in terms of surface energetics, by the advancing (maximum) contact angle THETA_adv and the receding (minimum) one THETA_rec. However, this empirical approach does not enable to quantitatively assess the surface energy of a solid (THETA_Y) because the

contact angle hysteresis on real solid surfaces is not sufficiently understood yet to permit the calculation of the equilibrium contact angle (THETA_eq) from hysteresis measurements.Some methods were suggested in the literature for calculating the Young contact angle from contact angle hysteresis. For heterogeneous surfaces, the average of the advancing and receding angles, THETA_adv and THETA_rec, is usually employed to estimate the equilibrium contact angle. A more thermodynamic alternative was proposed by Andrieu t al. [1]: the arithmetic mean of the cosines. Schulze et al. [2] suggested as estimation of THETA_Y for rough surfaces, the extrapolated value of the contact angle at zero hysteresis using the best-fit straight lines between THETA_adv or THETA_rec and the contact angle hysteresis H= THETA_adv-THETA_rec. However, this approach is also strongly empirical. We propose in this work a more physical model based on the validity of the Wenzel equation and the model of Shuttleworth and Bailey [3]. The Wenzel equation is fulfilled if the spatial period of asperities is much lower than the characteristic size of drop or the distribution of asperities is assumed uniform. Taking as inspiration the model of Shuttleworth and Bailey, the maximum and minimum values of apparent contact angle can be understood accordingly as deviations from the equilibrium contact angle:

THETA_adv = THETA_eq (H,f) +fH

THETA_rec = THETA_eq (H,f) + (1-f)H

where the factor f (0<=f<=1) informs about the asymmetry of the free-energy curve of the system around the global minimum, such that a symmetric energy curve is found for f=1/2. In order to relate the equilibrium contact angle to the Young contact angle, the Wenzel equation is required:

cos(THETA_eq) = r_W cos(THETA_Y)

in which we need to know the explicit relation between contact angle hysteresis and roughness: rW(H, f). This way, our model is based on a two-parameter non-linear fitting although it requires knowing the topographic pattern. We assumed a saw-tooth topographic pattern with different slopes.

Different data published in the literature have been analysed with the present model. Although Schulze's model and our model exhibit similar fitting goodness, our fitting parameters can be physically interpreted. For the ethyleneglycol-paraffin system, our model presents the best balance between statistical goodness and physical coherence, i.e. similar values of THETA_Y obtained from both fittings (THETA_adv and THETA_rec data). For this case, the f- factor is close to 0.5.

1 C. Andrieu, C. Sykes and F. Brochard, Langmuir, 1994, 10, 2077.

2. Schulze RD, Possart W, Kamusewitz H, et al. Young's equilibrium contact angle on rough solid surfaces, Part 1: An empirical determination. J Adhesion Sci Technol 1989;3:39-48.

3. Shuttleworth, R.; Bailey, G. L. J. Discuss. Faraday Soc. 1948,. 3, 16. -. 22.

1) Biocolloid and Fluid Physics Group, Department of Applied Physics, University of Granada, Campus de Fuentenueva; E-18071 Granada, Spain

2) The Rudolf Peierls Centre for Theoretical Physics, Oxford University, 1 Keble Road, Oxford, OX1 3NP, UK.

Study of Contact Angle Multiplicity of Cylindrical Drops Using Lattice-Boltzmann Model

The main challenge in surface thermodynamics is to quantify meaningfully surface energies of solids from multiple observable contact angles. This variability in contact angle arises from the non-ideal features of surfaces and it becomes manifest as contact angle hysteresis (CAH), pinning or contact angle multiplicity (CAM). If it is assumed that CAH, CAM and pinning were decoupled, they might be studied independently of each other [1]. In this work, we are focused on those systems with CAM but no CAH. In these systems, there is just one observable angle closely related to the concerning specific interfacial energies (material properties), at least on average. However, unless very particular conditions, this observable angle is hardly recognizable due to the corrugation of contact line. Instead, different effective angles have been proposed in the literature in order to estimate the thermodynamically meaningful contact angle. Although a more realistic three-dimensional calculation has already been reported [2], a simplified model can provide a more profound and a new insight into CAM problem. Cylindrical drops placed on smooth striped surfaces [3] were evolved using Lattice-Boltzmann model [4]. The strips were arranged perpendicularly to the drop axis in order to mitigate CAH and strengthen CAM. The drop size was chosen smaller than the capillary length so that the gravity was neglected. Once the mechanical equilibrium was realized, the shape of each drop was studied. It has been observed that the deformation of contact line is a function of intrinsic contact angles, pattern dimensions, surface tension, liquid-vapor interface width and line tension for small size drops, as expected. Furthermore, the effective angle computed from the apex curvature radius is related with the average value of solidliquid interfacial energy. Information on the local surface energy is only contained in the drop profile close to the triple line.

Figure 1: Profiles in different OY positions of the same cylindrical drop on a patterned surface with two stripes of intrinsic contact angles 120º and 30º. The boundaries are parallel to the OX edge. The profile in a) has been taken in a Y position where the intrinsc contact angle is 30º and the contact profile in b) istaken in a Y position where the intrinscic contact angle is 120º. Contact angle measured taking the top of the drop was 79,9º in both situations (Cassie angle is 79,5º). Extreme values of contact angle measured taking the profile close to the contact line were 41º in a) and 105º in b).

[1] M.A. Rodríguez-Valverde, F.J. Montes Ruiz-Cabello, M.A. Cabrerizo-Vilchez (2008) "Wetting on axially-patterned heterogeneous surfaces", In press. 10.1016/j.cis.2007.12.002 [2] I. Stanimir, N. P. (2006). "Nonaxisymmetric drop shape analysis and its application fro determination of the local contact angles." Journal of Colloid and Interface Science 301(2): 677-684.

[3] M. Iwamatsu (2006). "Contact angle hysteresis of cylindrical drops on chemically heterogeneous surfaces " Journal of Colloid and Interface Science 297(2): 772-777.

[4] A. Dupuis and J. M. Yeomans (2004). "Lattice Boltzmann modelling of droplets on chemically heterogeneous surfaces" Future Generation Computer System 20(6): 993- 1001.

Novel Applications of Switchable Superhydrophobic Surfaces

(Abstract not yet available)

1) Laser Zentrum Hannover e.V., Hollerithallee 8, 30419 Hannover, GERMANY

2) The Institute of Optics, University of Rochester, Rochester, New York 14627

Wettability Properties of Femtosecond Laser-induced Surface Micro- and Nanostructures and Their Influence on Fibroblast Cell Proliferation

Detailed investigations of wettability characteristics of femtosecond laser-induced surface micro- and nanostructures in silicon and platinum are performed. It is demonstrated that these structures suppress proliferation of fibroblast cells. Very good correlation between wettability characteristics and anti-adhesive fibroblast behaviour is found. This allows controlling and inhibiting proliferation of fibroblast cells on biomedical implants.

1. Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
2. Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.

Exploring Contact Angle Hysteresis and the Validity of the Cassie-baxter Equation Using Super-oleophobic Surfaces

Most natural and synthetic superhydrophobic surfaces derive their enhanced liquid repellency through the entrapment of air in their rough surface textures to form a composite (solid-liquid-vapor) interface. The Cassie-Baxter (CB) relation is widely used for predicting apparent contact angles of such composite interfaces. However, the validity of the classic CB relation has been challenged recently by McCarthy and coworkers. They suggest that the local configuration and distortion of the three-phase contact line, which is not considered specifically in the CB analysis, is responsible for significant discrepancy between the predicted and measured contact angles on patterned surfaces. We have recently used the concept of 're-entrant surface curvature' to design superoleophobic (oil-repellent) surfaces, and an intriguing corollary of the ability to construct oleophobic surfaces is that it becomes possible to directly image non-wetting three-phase interfaces in an electron microscope using non-volatile organic oils. Although our re-entrant textured surfaces are strongly oleophobic, the solid substrates themselves are weakly oleophilic, so there is substantial local contact line deformation at the foot of the liquid drop - which will amplify any discrepancies with the CB theory. We have microfabricated superoleophobic surfaces possessing three different kinds of surface textures - one-dimensional striped textures or 'grooves' that lead to strong droplet anisotropy, discrete solid pillars or 'hoodoos' dispersed between contiguous air regions and the corresponding 'reverse' structures. In each case, direct ESEM imaging shows severe local distortions of the tri-phase contact line. However, spreading experiments show that it is not the relative distortion of the composite interface per se, but the local pinning events and evolution of the contact line distortion during the advancing/receding motion of the drop that lead to the large observed discrepancies with the simple CB theory.

1) P.O. Box 1280; Hopewell Junction, NY 12533-1280

2) Boehringer-Ingelheim Pharmaceuticals, 900 Ridgebury Road, Ridgefield, CT 06877

In this work the authors review various definitions of acids and bases. Furthermore, the application of these theories to surface and adhesion science is discussed. It is clear that application of various acid-base theories may not always lead to consistent conclusions on the acid-base character of surfaces. Possible reasons for the inconsistency include the nature of the scale, the choice of reference points, the use of either poor or inconsistent statistical procedures in addition to experimental difficulties. The present authors recommend a future careful study and comparison of the various acid-base theories when applied to surface and adhesion science. The limited studies already preformed suggest this activity would be worthwhile.

Liquid Property Measurements Using Constant Diameter Nanoneedle-Tipped AFM Probes

In this report constant diameter metal alloy nanowires grown on AFM probe were used in micro-Wilhelmy measurements of surface tension and contact angle of low molecular weight liquids. Nanowires were between 5-70 microns in length and 50-500 nm in diameter. The deviation of the resulting surface tension was ~1-5 % of standard reported values of the liquids. Also, the F-D curves show well-defined stair-step events on insertion and retraction from wetting liquids, compared to the continuously growing attractive force of standard tapered AFM probe tips. In the AFM used, the stair-step feature in the F-D curve was stably monitored for nearly an hour, which provided height changes in the surface of the liquid from which the evaporation rate of even slowly evaporating liquids was determined. The constant diameter of the nanowires enabled the viscous damping by a liquid on the tip of a vibrating cantilever to be related to the equation of drag force for a cylinder, at a series of insertion depths, from which viscosity of the liquids varying from 1 to 1000 cP was measured with accuracies of 1-5 %.

E-mail: chuck_extrand@entegris.com

Super Wetting of Structured Surfaces

Super wetting of structured surfaces, sometimes referred to as hemi-wicking, was studied both experimentally and theoretically. Structured substrates with regular arrays of square pillars or frustra were machined from graphite blocks and then treated to render them lyophilic. Liquids spread over these surfaces to produce non-circular wetting areas. If the channels between the features were made shallower or narrower, liquids wicked more and spread over a larger area. The inherent wettability of the graphite was relatively unimportant -- large differences in contact angles had little influence on the spreading. Practically, this means to achieve extensive coverage, near-zero contact angles are not required. A combination of the appropriate surface structure and moderate inherent wettability can effectively flatten liquids, spreading them over very large areas.

fadeeval@shu.edu

Wetting of Hydrophobic Surfaces: Macroscopic and Microscopic Pictures

Wettability of well-defined organic monolayer surfaces of organosilanes on Si and organothiols on Au with systematic variations in hydrophobicity (water contact angles from ~0^o up to 115^o), monolayer thickness, and surface functionality has been investigated. The advancing/receding contact angles (_Adv/Rec) have been measured using wetting and non-wetting liquids, including water, formamide, ethylene glycol, methylene iodide, hexadecane, and acetonitryle. Also, the solid-liquid interfaces were characterized in-situ using ellipsometry. The ellipsometric data was consistent with the presence of the sub-nanometer gap layer at the solid-liquid interface for the surfaces with _Adv>90^o. For these surfaces, the gap thickness increased with the contact angle reaching ~ 1.2±0.2 nm for the surfaces with ~110-115^o (Fig). The presence of gap was not unique for water-hydrophobic interface: the gap was also observed for formamide, ethylene glycol, and methylene iodide on the CF₃-rich surfaces. The surfaces with <90^o demonstrated no gap with both aqueous and non-aqueous liquids. The results obtained suggested the fundamental relationship between the lyophobic repulsion (thickness of the gap) and the free surface energy (cos), providing microscopic definition of wettable (gap=0) and non-wettable surfaces (gap>0).

m.ferrari@ge.ieni.cnr.it

Adsorption of Surfactants at Superhydrophobic Surfaces in Air/Water and Oil/Water Systems

Superhydrophobic surfaces, with a water-contact angle greater than 150°, have attracted great interest for both fundamental research and practical applications. Due to the small contact area shown by these surfaces when in contact with water, interactions with aqueous environment are usually strongly reduced.

Chemical composition and geometrical structure of the surface are significant parameters governing the extreme hydrophobicity of the solid substrate. Here different superhydrophobic surfaces have been under investigation to study the effect of single surfactant solutions and mixtures on the wetting of these surfaces in air-water and oil-water systems.

The nature of the amphiphilic molecules and the substrate surface topography play important roles in research and technological fields also where the spreading control of the amphiphiles solutions is influenced by the distribution properties of the surfactant between two immiscible phases. By acting on the surfactant type and concentration, the spreading of a drop on a solid surface featuring a specific hydrophobic property can be controlled confining the volume by modification of physico-chemical parameters.

2) Chemistry Department, State University of New York at Binghamton, PO Box 6000, Binghamton, New York, 13902-6000, USA

Superhydrophobicity on Metal and Alloy Surfaces

We have developed a simple protocol for producing superhydrophobic surfaces with improved structural resistance and durability. The surface of metals and alloys were chemically etched to induce an appropriate surfaceroughness, and then chemically modified with a self-assembled monolayer of an alkane thiol, to reduce the intrinsic surface wettability. Surface roughness and low surface energy are key requirements for superhydrophobic behavior. Our superhydrophobic surfaces display water contact angles of about 165° and, at the same time, a hysteresis lower than 2° (Figure, right). These values are superior to those reported previously on metallic superhydrophobic surfaces Metallographic analysis (Figure, left) showed a strong influence of the chemical composition and grain distribution on the topography developed during etching. Etching conditions were manipulated to achieve the surface roughness required for superhydrophobic behavior (Figure, centre). The evolution of the surface topography was monitored by optical microscopy and revealed dramatic differences between the metal and the alloy, which both exhibited superhydrophobic behavior. Scanning electron and holographic microscopy as well as and laser and stylus profilometry were used to characterize the topography of the superhydrophobic surfaces.

Superhydrophobic Paper/Cellulose Surfaces Formed by Plasma Processing

Artificial superhydrophobic surfaces have been fabricated on numerous organic and inorganic materials such as polymers, glasses, metals and silicon. Considering substrate flexibility, cost and recyclability concerns, significant advantages may be realized if superhydrophobic surfaces could be generated on biodegradable substrates fabricated from renewable resources. In particular, if cellulose-based paper substrates can be rendered superhydrophobic, an extensive array of products such as food or beverage containers, self-cleaning cartons, labels, reduced fouling membranes, and microfluidic device structures could be manufactured from these low cost, flexible renewable materials. In this presentation, plasma processing sequences to generate both the appropriate roughness levels and surface energies required to establish superhydrophobicity on paper and other cellulose-based substrates will be described. The relative importance of physical surface roughness as compared to the chemical nature of the hydrophobic surface on cellulosic substrates will be indicated. Investigations to assess the mechanical and chemical stability of these surfaces will be discussed.

Contact Angles of Colloidal Particles Measured by a Novel "Film Calliper" Method

A novel experimental method for measuring the three-phase contact angle of individual colloidal particles at air-water and oil-water interfaces has been developed. The method utilizes the behaviour of colloidal particles when they are simultaneously attached to both surfaces of a free-standing thin liquid film thus forming stable particle bridges. The bridging particles spontaneously migrate to the film meniscus and accommodate at such a film thickness where the deformation of the fluid interfaces around the particles is practically missing. Measuring this thickness by optical interferometry and knowing the radius of a spherical particle allows us to calculate the particle contact angle by a simple formula relating these three quantities.

The applicability of the new method for measuring contact angles of hydrophilic particles of different sizes, wettabilities and chemical nature is demonstrated. The results obtained at the water-air interface are in excellent agreement with the contact angle values measured with alternative techniques. The film calliper method differs from the existing experimental techniques by its simplicity, reliability and applicability for measuring the contact angle of micrometer and sub-micrometer particles in real time without using artificial additives, sophisticated instruments or complex calculations.

E-mail: changfc@mail.nctu.edu.tw

Fabrication of Super-Amphiphobic Surfaces and New Type of Mold-Release Agent for Nanoimprint via Polybenzoxazine

A method for producing super-amphiphobic surfaces through plasma modification of benzoxazine films is presented. Micro-roughening and fluorination of the benzoxazine films occurs during the plasma treatment process and we fabricated a rugged surface with a micro/nano binary structure (MNBS). The combined effect of low surface energy and surface roughness results in high advancing contact angles (157° for water, 152° for diiodomethane) and low contact angle hysteresis.

On the other hand, one of the most important tasks remaining to be resolved in nanoimprint lithography is the elimination of the resist sticking to the mold during demolding. The previous approach was to apply a thin layer of fluorinated alkyl silane mold-release agent on the surface on the mold; however, this involves complicated steps and high costs. The low surface free energy material polybenzoxazine provides an efficient mold-release agent for silicon molds that is easier to process, costs less, and has no side reactions.

E-mail: doctorjx@sina.com

Research Progress of Hydrophobic Biomaterial Surfaces and Biomimetic Hydrophobicity Surfaces

Wettability is a fundamental property of a solid surface, which plays important roles in daily life, industry, and agriculture. Hydrophobic functional surfaces have aroused much interest because of their great advantages in many applications. Learning from nature gives us inspirations to construct functional surfaces with special wettability. In this paper the research results of some typical biomaterials with hydrophobicity, such as the self-cleaning effect of a lotus leaf and cicada wing, the anisotropic dewetting behavior on a rice leaf, the superhydrophobicity of a water strider's leg, and the hydrophobicity of soil animal cuticles, were reviewed. The surface characteristics of these biomaterials and their wettability mechanisms were discussed, the important research progress of biomimetic hydrophobicity surfaces were summarized, some main methods for adjusting surface wettability were introduced, the outlook for investigating biomaterial surfaces and biomimetic surfaces with special wettability was expected, and the important applications of artificial hydrophobicity surfaces were indicated.

e-mail: jianglei@iccas.ac.cn

Design and Creation of Bioinspired Surfaces with Special Wettability

Bio-inspired smart materials should be a "live" material with various functions like organism in nature, they must have three essential elements as sense, drive and control. Our recent studies are focused on the design and fabrication of bio-inspired surfaces with special wettability based on these ideas. The studies on lotus and rice leaves reveal that a super-hydrophobic surface with both a large CA and small sliding angle needs the cooperation of micro- and nanostructures, and the arrangement of the microstructures on this surface can influence the way a water droplet tends to move. Considering the arrangement of the micro- and nanostructures, the surface structures of the water-strider's legs were studied in detail. These results from the natural world provide a guide for constructing artificial super-hydrophobic surfaces and designing surfaces with controllable wettability. Accordingly, super-hydrophobic surfaces of aligned carbon nanotube films, aligned polymer nanofibers and differently patterned aligned carbon nanotube films have been fabricated. The large scale fabrications of super-hydrophobic polymer surfaces have been developed by modification of the traditional template method, the adoption of one-step coating and electrohydrodynamic processes respectively. Many of the methods had been applied in making superhydrophobic films with multi-functional properties, such as structural colored, transparent and/or conductive superhydrophobic films. Under certain circumstances, a surface wettability can switch between superhydrophilicity and superhydrophobicity, just like in Chinese ancient Taiji philosophy that "Yin" and "Yang", the two opposing fundamental properties of nature, are switchable. The cooperation between surface micro- and nanostructures and surface modification of poly (N-isopropylacrylamide) gave reversible switching between superhydrophilicity and superhydrophobicity in a narrow temperature range of about 10 °C. By grafting the copolymer of temperature-sensitive and pH-sensitive components on the surface, a dual-responsive surface that can be controlled by either or both of temperature and pH was fabricated. Besides the organic surfaces, a series of inorganic switchers were also made in our lab. UV light stimulated transition between superhydrophobic and superhydrophilic by aligned ZnO, TiO₂, and SnO₂ films are successfully prepared respectively. In addition, a dual-responsive WO₃ film with controlled wetting and Photochromism was obtained by an inexpensive and simple electrochemical deposition process. These studies have great application potentials in the fields of integrated micro-electronic devices, microfluidic control, trace bioanalysis and smart functional windows, etc..

Selected Publications:

1. Xuefeng Gao, Lei Jiang, Water-repellent legs of water striders, Nature, 2004, 432, 36.

2. Xinjian Feng, Lei Jiang, Design and Creation of Super-Wetting/Dewetting Surfaces, Adv. Mater., 2006, 18, 3063-3078.

3. Taolei Sun, Lin Feng, Xuefeng Gao, and Lei Jiang,

Bioinspired Surfaces with Special Wettability, Accounts of Chemical Research, 2005, 38, 644-652.

4. Lin Feng, Shuhong Li, Yingshun Li, Huanjun Li, Lingjuan Zhang, Jin Zhai, Yanlin Song, Biqian Liu, Lei Jiang, Daoben Zhu,

Super-hydrophobic Surfaces: From Natural to Artificial, Adv. Mater., 2002, 14(24), 1857-1860.

A Novel Design of Water- and Oil-Repellent Surface Modifier Having Double-Fluoroalkyl Groups

Fluorochemical polymers have been widely applied for water- and oil-repellent finishes because of the low surface energy of fluorocarbon. The repellency of fluorocarbon finishes depends on the structures of fluorocarbon segment, the nonfluorinated segment of the molecule, the orientation of the fluorocarbon tail, the distribution and the amount of the fluorocarbon moiety on surface. In this work, we have developed the effective and powerful fluorochemical water- and oil-repellent polymers based on the new concept of introduction of double fluoroalkyl segments per monomer unit.

Effect of double-fluoroalkyl structure on the orientation of the fluorocarbon tail was evaluated from the monolayer behavior (the surface pressure - Area measurement) of newly designed acid 1, diester of 2, 2-bis(hydroxymethyl)-propanoic acid with C₈F₁₇(CH₂)₁₀COOH. In this acid, two fluoroalkyl segments are end-capped on trimethylene chain. As expected, the rigid monolayer of acid 1 was formed on water at even the elevated temperature.

Next, though most polymeric fluorine-containing repellents contain only one fluorocarbon segment per monomer unit, we synthesized the methacrylate monomer having two (double) fluoroalkyl segments using HEMA and acid 1, and polymerized. Using this double-fluoroalkyl polymer 2, we prepared the cast film of PMMA containing polymer 2. Based on the contact angle measurements of decane and water on the cast film, the surface was found to be modified highly water- and oil-repellent even at the minimum additive amount of double-fluoroalkyl polymer (0.01 wt%/PMMA). The effectiveness was also estimated on the basis of Cassie-Baxter equation, and the alignment of double-fluoroalkyl groups on the surface was discussed.

Effects of Water and Alcohol Adsorption on Silicon Oxide Nano-asperity Adhesion

As the size of the contact decreases to the nano-scale, the measured contact forces become more sensitive to the molecular adsorption from gaseous environments. This talk will discuss the effects of water and alcohol adsorption on the adhesion force measured with atomic force microscopy (AFM) for the single-asperity contact between silicon oxide surfaces. As relative humidity (RH) increases, the adhesion force measured with AFM initially increases, reaches a maximum, and then decreases at high RH. Traditionally, this RH dependence has been attributed to the capillary force caused by the water condensation at the AFM tip-surface contact. However, the capillary force alone cannot explain the observed magnitude of the RH dependence. The origin of the large RH dependence is due to the presence of a solid-like structured water adsorbed at the silicon oxide surface at room temperature. Spectroscopic evidences of the solid-like structured water on the silicon oxide surface and a solid-adsorbate-solid model developed to calculate the contributions from capillary forces, van der Waals interactions, and the rupture of an ice-ice bridge will be discussed. In the case of alcohol adsorption, there is no solid-like phase formation. In this case, the capillary force plays a significant role in the dependence of the measured adhesion force on the alcohol partial pressure in the gas phase. The magnitude of the capillary force at any given temperature and adsorbate partial pressure depends primarily on four factors: the surface tension of the adsorbate, its liquid molar volume, its isothermal behavior, and the contact geometry. At large contacting radii, the adsorbate surface tension and the contact geometry are dominating. This is the case of surface force apparatus measurements and AFM experiments with micron-size spheres. However, as the size of contacting asperities decreases to the nano-scale as in AFM experiments with sharp tips, the molar volume and isotherm of the adsorbate become very important to capillary formation as well as capillary adhesion. This effect is experimentally and theoretically explored with simple alcohol molecules (ethanol, 1-butanol, and 1-pentanol) which have comparable surface tensions but differing liquid molar volumes.

E-mail: m.kohonen@hull.ac.uk

Observations on Insect Adhesion and Friction

The amazing ability of insects to adhere to a broad variety of surfaces is well known. The ability to attach and detach at will enables insects to forage in a highly variable environment, and also provides the means for attack and defence. A better understanding of insect adhesion and friction mechanisms may provide valuable clues in the development of new adhesives, smart friction devices and environmentally friendly methods of insect control.

We have recently established a multidisciplinary project aimed at understanding how surface properties affect the ability of insects to adhere to, and move along surfaces. In this presentation I will briefly summarise what is known about insect adhesion and friction mechanisms, and then describe the results of some of our recent experiments with various species of ants.

lewisd2@rpi.edu

Computational Method for Understanding Balance of Surface Tension Forces Against External Constraints of Varying Complexity

The shape of soap bubbles, red-blood cells, solder joints, droplets on hydrophobic surfaces, and grain growth all depend on the balance of surface tension forces against external constraints of varying complexity. Surface Evolver has improved our ability to predict the equilibrium geometries in these physical systems. This talk will examine different examples where the impact of Surface Evolver has led to increased understanding and will speculate on the future utility of this calculation technique.

Fibre Surface Engineering and the Link Between Fibre Wettability and Wet Adhesion

(Abstract not yet available)

Superhydrophobic Electrospun Nonwovens

Electrospinning has emerged in recent years as a relatively easy, efficient and robust method to make ultrafine continuous fibers with diameter on the order of 10 nm - 10 um from a variety of materials. We recently discovered electrospun fiber mats have the appropriate surface roughness for superhydrophobicity. We have developed multiple ways to make superhydrophobic surfaces in the form of flexible, breathable and free-standing nanofibrous membranes composed of electrospun fibers. Based on an understanding of the role of fibrous structure to create a surface of suitable topology, we also developed strategies to enhance the superhydrophobic property and its robustness by carefully designing the surface nanostructures of individual fibers. Superhydrophobic fibrous membranes with other functionalities such as structural color will be highlighted.

Super-hydrophobicity: Water in Air, and Air in Water

(Abstract not yet available)

Email for correspondence: glen.mchale@ntu.ac.uk

Superhydrophobicity: Localized Parameters and Gradient Surfaces

The use of Casssie and Baxter's equation and that of Wenzel have come in for some criticism of late.¹ It has been suggested that researchers use the equations mechanically without always considering the assumptions that have been made and sometimes apply them to cases that are not suitable. This debate has prompted a reconsideration of the derivation of these equations using the concept of parameters for the roughness and Cassie-Baxter solid surface fractions that are local to the three-phase contact lines.² In such circumstances, the roughness and Cassie-Baxter solid fractions depend not only on the substrate material, but also on which part of the substrate is being sampled by any given droplet. This is not simply a theoretical debate, but is one which has direct consequences for experiments on surfaces where the roughness or spatial pattern varies across the surface. This leads us on to experimental results using such surfaces. In particular, using a variation in roughness across a surface possessing a constant surface chemistry, we show different contact angles on each side of a droplet of water placed on it can generate sufficient lateral force for the droplet to move towards the lowest contact angle region. In principle, paths can be defined and water droplets can be collected by defining gradients in superhydrophobicity through changes in the lateral topography of the surface.

References

1. Gao, L.C.; McCarthy, T.J. (2007). How Wenzel and Cassie were wrong, Langmuir, 23, 3762-3765.

2. McHale, G.; (2007). Cassie and Wenzel: Were they really so wrong?, Langmuir, 23, 8200-8205.

Wetting of Microspheres and Nanotubes Using the AFM

An atomic force microscope (AFM) is used to measure the meniscus force on microspheres and nanotubes as the material is pulled through an air/liquid interface. A fluid bridge forms between the liquid and the material as it is pulled out of the liquid. The force reaches a maximum as the bridge necks down and finally detaches from the surface. The maximum force on the material can be used to calculate the surface tension of the liquid. This and the wetting force allow the contact angle of the liquid to be calculated. Contact angle hysteresis was observed as the material was pushed into the droplet. In addition, capillary waves are observed when the material first touches the liquid interface.

*Email: W.Ming@unh.edu

1) Nanostructured Polymers Research Center, Materials Science Program, University of New Hampshire, Durham, NH 03824, USA

2) Lab of Materials and Interface Chemistry, Eindhoven University of Technology, P. O. Box 513, 5600 MB Eindhoven, THE NETHERLANDS

Superoleophobic Surfaces

The well-known self-cleaning property of some plant leaves is due to a combination of low surface-energy species and a unique dual-size surface topology. We have successfully mimicked the dual-size structure by incorporating nano-raspberry-like silica particles to conventional polymer films, which have been effectively turned superhydrophobic. On the other hand, oil repellency is critical in maintaining self-cleanability for a superhydrophobic surface. We further examined the feasibility to achieve superlipophobicity on surfaces with multi-length-scaled structures, and have successfully obtained superoleophobic polymeric films and cotton textiles.

Woo-Il Lee², Jong-Kyoo Park³, K. Lawrence DeVries⁴

1) School of Nano and Advanced Materials Engineering, Engineering Research Institute, Gyeongsang National University, Jinju 660-701, KOREA

2) School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, KOREA

3) Agency for Defense Development, 4-R&D Center Daejeon 305-600, KOREA

4) Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah 84112, U. S. A.

Interfacial Adhesion Evaluation and Self-Sensing of Single Carbon Fiber/Carbon Nanotube-Epoxy Composites Using Electro-Micromechanical Technique and Dynamic Contact Angle Measurement

Interfacial adhesion and self-sensing were investigated with different dispersion solvents for single carbon fiber/carbon nanotube (CNT)-epoxy composites by electro-micromechanical technique and dynamic contact angle measurement under loading/subsequent unloading. The optimized dispersion procedure was set up to obtain improved mechanical and electrical properties. Apparent modulus and electrical contact resistivity for CNT-epoxy composites were correlated with different dispersion solvents for CNT. CNT-epoxy composites using good dispersion solvents exhibited a higher apparent modulus because of better stress transferring effects due to the relatively uniform dispersion of CNT in epoxy and enhanced interfacial adhesion between CNT and the epoxy matrix. However, good solvents exhibited a higher apparent modulus but lower thermodynamic work of adhesion, W_a for single carbon microfiber/CNT-epoxy composite. It is attributed to the fact that hydrophobic behavior with high advanced contact angle was observed for CNT-Epoxy in the good solvent, which might not be compatible well with the carbon microfiber. Damage sensing was also detected simultaneously using AE combined with electrical resistance measurement. Electrical resistivity increased stepwise with progressing fiber fracture due to the decrease in electrical contact by the CNT.

( Acknowledgement: This work was supported by Defense Acquisition Program Administration and Agency for Defense Development under the contract UD070009AD.)

1) Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, JAPAN

2) Kanagawa Academy of Science and Technology, JAPAN

anakajim@ceram.titech.ac.jp

Direct Evaluation of the Sliding Motion of Water Droplets on Hydrophobic Silane Coatings

Self-assembled monolayer (SAM) coatings of hydrophobic organosilanes have been widely used for surface modification of inorganic materials. In this study, we prepared various silane coatings with different surface morphology and compositions on Si substrates. Then, the relationship between surface characters (surface roughness, chemical composition, and homogeneity of assembly) and static or dynamic hydrophobicity on the surface were investigated. The internal fluidity of a sliding water droplet on tilted solid surfaces were directly observed using particle image velocimetry (PIV) method with a sheet-shaped laser beam and fluorescent particles. This analysis revealed that sliding acceleration in the early stage of constant acceleration region is dividable into two different components, rolling and slipping motions. The slipping/rolling ratio of sliding acceleration depended on surface morphology and homogeneity of silane coatings. Slipping velocity and acceleration became larger when a droplet slid down on smooth and homogeneous coatings. Detailed analysis clarified that the slipping motion played an important role for entire water shedding kinetics.

1) Advanced Engineered Wood Composite (AEWC) Center, University of Maine, Orono, ME 04469, USA

2) Centro de Investigación de Polímeros Avanzados-CIPA, Universidad de Concepción, Edmundo Larenas 234, Concepción, CHILE

Adhesion Properties of Wood Plastic Composites Surfaces (WPC) Using Atomic Force Microscopy

The adhesion properties of the individual components of Wood Plastic Composites are highly relevant in determining their compatibility and in case of Wood Plastic Composites boards to determine their potential application as structural components. Preliminary results indicate that WPCs have low surface energy, mainly because of the migration of the lubricant added during their processing to the board surface (G. Oporto et al., Journal of Adhesion Science and Technology 21, 1097-1116(2007)). Different treatments were performed on the WPC to increase their wettability, and those included chemical, mechanical and energetic modifications. Macroscopic analysis was performed through contact angle determinations and surface energy calculations using two different models. In this paper, a microscopic analysis was performed using Atomic Force Microscopy (AFM) to determine adhesion properties of WPC composites and individual components before and after a corona discharge treatment, and a correlation between the macro and microscopic adhesion behavior will be discussed. For the microscopic analysis, non functionalized and functionalized tips (hydroxyl, methyl and carboxyl attached groups) were used to determine pull-off forces (adhesive forces) during an AFM contact mode experiment. Histograms of the adhesion forces were determined after a series of more than one hundred force curve determinations. Additionally, short and long range forces were determined using a dual AC AFM mode operation.

1) University of Ljubljana, Biotechnical Faculty, Dept. of Wood Science & Technology, Jamnikarjeva 101, SI 1000, Ljubljana, SLOVENIA

2) Laboratoire d'Etudes et de Recherches sur le Materiau Bois, University Henri Poincare Nancy I, Faculty of Sciences, Vandoeuvre-les-Nancy, FRANCE

Wettability of Various Wood Based Materials and Their Surface Free Energies

Dynamic contact angle measurements of test probe liquids and several solventborne and waterborne wood coatings on wood based materials are presented and discussed. Contact angles were determined by the Wilhelmy plate method. The substrates were different wood species (beech, pine and spruce); chemically and thermally modified wood; and wood, modified by viscoelastic thermal compression. The increased hydrophobic character of modified wood was revealed from high advancing contact angles of water. In contrast, waterborne coatings exhibited much better wetting on modified substrates then on unmodified ones. Good wetting of modified wood by waterborne coatings is an interesting result, opening possibilities for applications of environmentally friendly waterborne surface finishing systems on modified wood. In addition, surface free energies of unmodified and modified wood were investigated, using the Lifshitz van der Waals/acide-base approach. The results were related to chemical changes of wood components due to modification processes.

CASTI, CNR-INFM Regional Laboratory, Department of Physics, University of L'Aquila, via Vetoio, 67010 Coppito- L'Aquila - ITALY

¹ NANO-Center for Advanced technologies S.r.l, Department of Physics, University of L'Aquila, via Vetoio, 67010 Coppito- L'Aquila - ITALY

e-mail: phani_ayala@yahoo.com

Super Hydrophobic Films Based on Organic-inorganic Hybrid Coatings - Potential Application in Aeronautic, Automotive and Biomedical Applications

Organic-inorganic hybrid materials can offer multifunctional properties tailoring from submicrometer to nanometer length scales in various applications such as micro and nano photonic devices including, waveguides, light emitting devices, quantum dot devices, photonic band gaps and holographic materials. In the present investigation, hybrid materials based on methyltrimethoxy silane, phenyltrimethoxy silani, perfluorolky silanes, fluorine based polymers, polyvinyl chloride based polymers were spin / dip coated on to different substrates glass, quartz, and polycarbonate substrates at room temperature. The deposited films have been cured under UV irradiation for better polymerization followed by annealing at 100^oC (for polycarbonate), 200^oC and 300^oC (for other substrates) for 30 minutes. To improve the scratch resistance properties of these coatings nanoscale silica nanospheres have been incorporated into the matrix by sol-gel process. UV-visible spectroscopy (UV-vis), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) have been used for optical absorbance, vibrational and stretching bands, and phase formation of the deposited of the films, respectively. The deposited films are transparent, hard, scratch resistance and in particular hydrophobic. Friction coefficient measurements have been carried out by using steel and Al₂O₃ as counter bodies. Adhesion strength failure and hardness measurements on plastic substrates were examined by using scratch resistance tester and nanohardness tester, respectively. These developed hydrophobic nanostructured coatings with multifunctional properties can be applied on to monuments to protect the surfaces from dirt, and dirt rainy water. Apart from these nanostructured coatings find applications in the protection of surfaces such as tiles, wood, metal, plastic, glass their by applying in different industrial sectors.

1) Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

2) School of Materials, Arizona State University, Tempe, Arizona 85287;

3) Harrington Department of Bioengineering, Arizona State University, Tempe, Arizona 85287.

Design of Surfaces with Photo-induced Superhydrophilic to Superhydrophobic Switching

This presentation will describe the design and study of nanowire surfaces functionalized with photochromic monolayers for which the wetting angle of liquids can be reversibly switched by more than 100 degrees. In these studies we introduce a modified wetting model to predict the apparent contact angle for complete wetting of rough surfaces based on the measured angles on the corresponding smooth surface which provides better agreement with experimental data. This modified model corrects for the missing aspect of the Wenzel model that the critical angle for liquids to penetrate pores on rough surfaces is typically observed to be below 90°. We compare our model with experiment using aqueous dimethylformamide solutions over the full range of wetting angles on smooth Si surfaces and rough Si nanowire surfaces coated with a photochromic azobenzene monolayer. Our modified model shows excellent agreement with the experiments as well as with previously published data. We demonstrate how this model can be used to help design and optimize the amplification of light induced contact angle changes on a rough surface. The control of wetting behavior is illustrated for surfaces with nanowires of varying lengths and surface density, corresponding to different levels of roughness. At the greatest roughness we achieve optical switching between the extreme cases of superhydrophilic and superhydrophobic wetting.

1) Département des sciences du bois, Université Laval, Québec, CANADA

2) FP Innovations, Forintek Division, Québec, CANADA

3) Centre for Advanced Wood Processing, Faculty of Forestry, Vancouver, CANADA

Plasma Treatment for Enhanced Adhesion of Coatings to Wood

Wood is a standard construction material in North America. Indoors and especially outdoors, coatings are necessary to maintain appearance and color and protect from UV radiation, water and oxidation. Coatings can be water or solvent-based and contain a high solids content.

In general in polymer materials there are now commercials systems to treat plastics with different plasma or corona type treatments to enhance adhesion of paints and inks. These treatments use different gases: water, oxygen, nitrogen, argon and mixes of these. Plasma can be of 'cold' type, and even partly 'atmospheric' in continuous systems. In preliminary work we have determined that nitrogen plasma treatment as well as simply exposing wood to vacuum lowers adhesion (as measured with pull-off tests) and increases water contact angle, while some other plasmas, such as those derived from nitrogen-hydrogen mixtures and water vapour, enhances adhesion and lowers water contact angle. These effects can be correlated with contact angle measurements and photoelectron spectroscopy results. There was little change in the appearance of wood as measured through color (Lab) measurements.

Moving Contact Lines: Can the Interfacial Width Remove the Stress Singularity?

Extensive molecular dynamics (MD) simulations of partially miscible binary fluids are used to study the effect of interface width, surface tension and flow boundary conditions on the dynamics of contact lines. Recent theoretical work suggested that for broad interfaces, diffusion could balance the advective flow near the contact line and thus eliminate the stress singularity from the no-slip boundary condition. This requires diffusive flux perpendicular to the fluid interface, while our simulations show that the diffusive flux is parallel to the interface. Moreover, we find that results for the apparent dynamic contact angle are only a function of the capillary number and the slip length describing the flow boundary condition far from the contact line. Changing the interface width and surface tension by an order of magnitude or more does not affect this relation or indicate a role of diffusion. In contrast the slip boundary condition has a pronounced effect on the contact angle. All simulations show a first order transition to entrainment at a contact angle of about 135 degrees.

Effect of Line Tension on the Work of Adhesion for Rock-oil-brine Systems

In a recent experimental study, the concept of line tension has been evaluated for rock-oil-brine systems at reservoir conditions to characterize the rock-oil adhesion interactions. This study suggests that line tension-based modification of the Young's equation provides a more realistic description of rock-oil adhesion interactions at reservoir conditions. These experimental findings suggest that effect of line tension should be incorporated in the calculation of work of adhesion for better understanding of the effect of adhesion forces on oil recovery from the petroleum reservoirs. In this present experimental study, we would like to report our efforts to calculate the work of adhesion for different rock-oil-brine systems after incorporating the effect of line tension on the work of adhesion.

Measurement of line tension and its effect on the work of adhesion for several rock-oil-brine systems has been investigated using actual conditions and fluids from different petroleum reservoirs. The work of adhesion has been calculated for each of the systems studied after incorporating the line tension effect on it. This experimental study suggests that the traditional approach of determining the work of adhesion for rock-oil-brine systems undermines its impact on rock-oil interactions. The calculation of work of adhesion for different rock-oil-brine systems after incorporating the effect of line tension suggests that adhesion forces are much stronger than predicted conventionally.

The Porosity and Wettability Properties of Hydrogen Ion Treated Polytetrafluoroethylene

(PTFE) materials are evaluated using optical transmittance, contact angle, SEM, and FTIR tests. The materials are irradiated using a low energy hydrogen ion shower (LEHIS) produced by a Gas Discharge Ion Source (GDIS). Mass spectrometry shows the ion shower constituents to be *H**+ *and 2 *H*ǽ where the monatomic ion is the dominant species. The duration of treatment and ion shower energy are varied to determine their effects on the PTFE specimens. The ion shower energy is varied by changing the plasma discharge current (Id) at intervals of 1 mA. Results show treatment using lower Id improved material hydrophobicity and IR-absorbance while higher Id resulted in enhanced hydrophilicity and slightly lower IR absorbance. Transmittance and wettability are found to have a positive correlation, i.e., a wettable surface is determined to be optically transmissive as well. SEM images showed that as the surface of the material roughens, its optical transmittance, wettability, and surface tension increased. The surface modification is essentially morphological as there is no observable shifting of the IR absorption peaks.

Superhydrophobic Binary Structures: Preparation, Characterization and Ice Adhesion

Substrates consisting of micro-patterns have been created by chemical etching. Nanolayers of RTV silicone rubber films with varying thickness have been coated by spin-coating method and nanolayers of fluorinated hydrocarbon films with varying thickness have been deposited by plasma enhanced chemical vapour deposition (PECVD) method on the existing micro-patterned substrates to achieve binary structures. The morphological studies have been carried out by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The compositional study has been performed by Fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The comparative study on the superhydrophobicity achieved by these methods will be discussed in the present paper and the results on the ice adhesion on these superhydrophobic binary structures will also be discussed.

1) Université Bordeaux 1, Laboratoire de Mécanique Physique, CNRS UMR 5469, 351 Cours de la Libération, 33405 Talence Cedex, FRANCE

2) University of Edinburgh, School of Engineering and Electronics, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JL, UK

Kinetics of Triple Line Motion during Evaporation

A sessile drop evaporating in an unsaturated environment may change shape in various ways. Under some circumstances, the wetting triple line (WTL) stays static on the solid surface for a while, leading to a decrease of contact angle. The WTL then recedes quickly, causing increased contact angle. "Stick-slip" cycles then ensue.

Wetting hysteresis of sessile drops of ethanol on a randomly rough PTFE has been studied. The above mentioned stick-slip behaviour has been clearly seen. Periods during which the wetting triple line is static, maintaining constant drop contact radius, but leading to decreased drop height and contact angle, are followed by a period of receding wetting accompanied by increasing contact angle and height.

A simple model using excess free energy as a criterion for stick-slip behaviour has been applied. Basic features of the model and experiment correlate well. We explain the order of magnitude of the "pinning" time. However, there is more variability in the slip time. This has been tentatively attributed to the non-simultaneous attainment of the slip threshold around the drop.

Slip distances diminish approximately with the square root of contact radius. Analysis of final drop disappearance behaviour suggests a hysteretic energy barrier of ca. 10^-6 N, comparable with reported values of line tension.

1) Kyowa Interface Science Co., Ltd., Niiza-City, Saitama 352-0011, JAPAN

2) Exponential Business and Technologies Company, Savage, MN 55378, USA

Contact Angle Measurement in Reduced Spatial and Time Domains

The famous lotus self-cleaning phenomenon and its understanding have stimulated strong interests of biomimetic scientists and researchers in synthesis of artificial materials and structures. Advanced patterning techniques, novel materials, nanoparticles and nano thin films have been explored for simulating the lotus phenomenon or modifying material surface hydrophobicity and hydrophilicity. Meanwhile, micromanufacturing has gained increasing recognition in modern manufacture along with increase in applications of microdevices such as microelectromechanical system (MEMS). One of the challenges faced by these researchers in the fields of micro/nanoscience is the transition from continuum mechanics to quantum mechanics. Many known and accepted theories may not be readily applicable to the phenomena observed at micro and nano scales any more. Development of new theories, study of new phenomena and measurement of properties of real parts with small dimensions has prompted development of many new research and measurement tools.

In this paper a micro contact angle meter specially designed for the pioneers in the micro/nano fields is introduced. The instrument is equipped with a unique capillary liquid dispensing system that has an inner diameter of 5-50µm and optionally an ink-jet nozzle with piezo drive, for making a liquid drop <100µm in size and picoliter in volume. In addition, the instrument comes with high magnification optics; one is for top view and for accurately placing a droplet on a micro area, and the other for measuring such small drops on micrometer features. CCD cameras with extremely high capturing speed up to 100,000 frames per second are available for recording instantaneous and transient phenomena.

The unmatched instrument capabilities and usefulness for contact angle measurement at microscale are exemplified through results obtained on fiber, patterned organic light emitting display and microcircuits. Its advantageous high speed capturing capability is demonstrated by measuring the strong dependency of contact angles on time at tens of microsecond intervals. The recorded feature-rich dynamics of contact angles of micron size drops is deemed valuable for investigating vapor evaporation, wetability, absorbing, and hydrophilicity/hydrophobicity changes at micro/nano scales.

1) Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY; Email: info@dtnw.de

2) GMBU e.V. - Arbeitsgruppe Funktionelle Schichten, Bautzner Landstraße 45, D-01454 Großerkmannsdorf, GERMANY; E-mail: mahltig@gmbu.de

Durable Nanosol Coatings for Textiles Combining Hydrophobicity and Antistatic Properties

For many reasons, electrostatic charging of textile materials is a serious problem. The effect is caused mainly by friction or charge separation. Charge separation occurs in technical processes, where goods are removed from textile belts, or in simple everyday activities such as walking over carpets made from synthetic fibers. The resulting electric potential may be as high as 35,000 V and the eventual discharge may be accompanied by spark formation, e.g., if the charged textile is in proximity to zero potential surfaces such as a door. While discharging is more a convenience problem in everyday situation, the formation of sparks means a serious hazard in industrial environments, since it might ignite inflammable dust, liquids, or gases, respectively.

Today, a wide range of commercial finishing products is available to prevent an electrostatic charging by increasing (surface) conductivity. The finishing materials show a very low durability, however, and have to be re-applied regularly. Simultaneously, the common antistatic finishes increase the wettability of the textiles and therefore lead to an increased soiling.

It is well known that sol-gel technology allows to prepare nanocomposite coatings that offer far reaching possibilities for surface functionalization. The paper summarizes results of a present research project dealing with the development of durable nanosol coatings which combine a satisfying soiling behavior and a surface conductivity that meets the specification for antistatic materials. The concept relies on the preparation of alkoxysilane based networks that are modified with certain combinations of hydrophilic and hydrophobic components.

1) Technische Universität Dresden (TUD), Institut für Werkstoffwissenschaft, Dresden, GERMANY (Dresden University of Technology, Institute of Materials Science, Dresden, GERMANY)

2) TUD, now at: Unicamp, Campinas, BRAZIL

3) Leibniz Institute of Polymer Research Dresden, Dresden, GERMANY

4) GVD Corporation, Cambridge, MA, USA

Superhydrophobic Aluminum Surfaces: Preparation Routes, Properties and Artificial Weathering Impact

Among the materials that can show superhydrophobic properties are hydrophilic metals which must undergo a sequential treatment, including roughening and hydrophobic coating.

This contribution presents various preparation routes, which involve pure and alloyed aluminum as the substrate. Micro-rough surfaces were generated most easily by using a special sulfuric acid anodization (SAAi), which produces a micro-mountain-like oxide morphology with peak-to-valley distances of 2 µm and sub-µm roughness components. This initial state may be combined with a number of wet-born coatings both of low-molecular and of polymer nature, e.g. alkyl phosphonic or carbonic acids, reactive alkyl silanes, Teflon^® AF or the reactive polymer POMA containing a long alkyl side group. Additionally, it was successfully demonstrated that the chemical modification can also be done by the Hot Filament CVD of a PTFE layer. The latter can form a fundamentally higher thickness of up to 1 µm, without any leveling of the microprofile of the substrates. However, the inherent and controllable morphology of the PTFE layers represents an important feature.

In addition to contact angle measurements (CA) and scanning electron microscopy (SEM), various spectrometric techniques (FT-IRRAS, XPS, EIS) were employed in the characterization process. Further, the impact of a standardized artificial weathering was determined and is discussed in terms of possible damage mechanisms.

Nonextensive Approach of Thermodynamics to Wettability

(Abstract not yet available)

Grafted Zno Surface (Superhydrophobic Surface)

(Abstract not yet available)

Wettability Behavior of Acid-Base Surface

(Abstract not yet available)

Energetics and Kinetics of Specific Ligand-Receptor (Including Antigen-Antibody) Interactions

Specific ligand-bearing peptides with pre-existing) (i.e., innate) anti-microbial specificities exist in the entire biological realm, from humans and other animals, plants, molds and bacteria. One example of these is lysozyme, discovered in 1920 by Sir Alexander Fleming. In the same, innate, category as these peptides are the omni-present lectins, which are proteins or glycoproteins (with specificities against carbohydrates), such as human blood cell antigens, with Concanavalin A as a major example.

Defense macromolecules with specific ligands of a more recent vintage (from an evolutionary point of view) are antibodies (Ab) whose specificities are adaptive (i.e., acquired during the host's life); these are created after a first encounter with the antigens (Ag) of given invading foreign infectious agents. Ab's are blood serum proteins with both adaptive and innate properties. The specific ligands (paratopes) of Ab's comprise about six amino acids and are concave and often relatively hydrophobic; they can fit into the complementary shaped combining sites or receptors (epitopes) of Ag's, which are convex and hydrophilic.

The forces between paratopes and epitopes are various combinations of the three non-covalent Lifshitz-van der Waals (LW), Lewis acid-base (AB) and electrostatic (EL) forces. The optimal specificity of the interaction between an Ag and its specific Ab, is reached by achieving the best fit and therefore the shortest distance, between the contactable surfaces of the protruding epitope and the hollow paratope, resulting in the strongest possible binding energies. The energetics and kinetics of Ag-Ab binding are similar to those of the physical adsorption between, e.g., macromolecules and solid surfaces, when immersed in water.

The binding energy is proportional to the natural logarithm of the equilibrium binding constant (i.e., ln K_a), where:

K_a = k_a/k_d

and where k_a and k_d are, respectively, the kinetic association (a) and dissociation (d) rate constants. It has been shown experimentally that the great variability between the binding energies among different specific ligand-receptor systems is mainly function of the kinetic dissociation rate constant, k_d, i.e., of the ease or difficulty, or more precisely the speed, with which the ligand and receptor will separate from one another, immediately after having been bound together. This is also the case in, for instance, protein-silica adsorption systems, where some of the pertinent data were based on contact angle measurements.

E-mail watanabe@wlab.rcast.u-tokyo.ac.jp

Surface Wettability Control by Photocatalysis for Self-Cleaning

In the last decade, self-cleaning technology utilizing surface wettability control has made advanced greatly. Photo-inducecd hydrophilic conversion has been found by our group for the first time at 1995. Now, it has applied for various industrial uses for self cleaning surface.

On the other hand, superhydropobic surface is attracting much attention not only from scientific viewpoint, but also from application viewpoint. Well known Cassie equation shows that superhydropobic surface can be obtained by surface roughness control of polymer material. However it is very hard to obtain mechanical tough superhydrophobic material because of its porous structure. Therefore, super hydrophobic material has been commercialized only for limited applications such as anti-snow sticking uses.

Even though the contact angle is not so much high as like superhydrophobic, we can control a sliding angle of water droplet instead by optimizing surface structure of thin film. For self-cleaning uses, removal performance of water is more important than water repellency. To optimize surface structure and utilizing photocatalysis, we have succeeded to design the inorganic surface whose sliding angle is only 20 degree recently and high water removal property. It also exhibits photocatalytic self-cleaning effect.

In this paper, we describe the recent progress of the surface wettability control technology for self-cleaning.

High Temperature Capillarity in Metal Systems: Insights from Atomic Modeling

The wetting and spreading of metal liquids on metal or ceramic substrates is typically associated with reaction between the liquid and solid. Inter-compound or inter-metallic formation, surface alloy formation, and/or substrate dissolution into the liquid are prominent examples of reactions exhibited by a large number of high temperature capillary systems. Debate about the influence of reactions on spreading exists since, for some systems, spreading rate does not correlate with the free energy of the corresponding reaction whereas for other systems, correlation appears to exist. This talk will review atomic scale calculations of spreading in a number of metal binary systems exhibiting different types of reaction between the liquid and solid as well as varying degrees of reactivity. Kinetics of spreading will be presented along with observed relationships between kinetics and reactivity. The power of an atomic scale method is in revealing specific atomic mechanisms associated with spreading and how those phenomena are influenced by the ongoing reaction. Mechanisms will be discussed in context of the corresponding kinetics elucidated by the model as well as existing theoretical descriptions for relevant systems.

Using Monolayer Coatings to Tune Surface Wettability

Monolayer coatings, such as polymer brush coatings or self-assembled monolayers, are a very attractive means to tune the surface characteristics of a material without altering the inherent properties or appearance of a product. TNO has a research program on developing these types of coatings and applying them on glass, metal, polymer or textile substrates, to make the product more repellent to water, dirt or bacteria. Optimizing processing conditions for coating application is crucial for the durability and functionality of the coating. The product properties are tailored by the polymer brush coating, consisting of a monolayer of polymer chains covalently attached to a surface, and are dependent on the type of polymer used as well as on the grafting density. An example of such a coating is a hydrophilic brush coating to prevent adhesion of bacteria and blood platelets, which may be used in medical devices like catheters and stents. A similar approach has been developed for the hydrophobic functionalization of textiles where water contact angles of over 155 degrees can be obtained.

A Novel Ultra-Hydrophobic Surface: Statically Non-Wetting but Dynamically Non-Sliding

In this study, we try to give a more complete definition about superhydrophobicity. We report the fabrication of a novel surface with both morphology and composition heterogeneities by casting polymer blend solution. The resultant poly (methyl methacrylate) (PMMA) and amphiphilic polyurethane (A-PU) surface has a rough structure on microscale and separated hydrophobic and hydrophilic nanodomains as well. On this surface, water drop shows a static CA about 160 but the drop is pinned on the surface at any titled angles. This phenomenon can be ascribed to the special surface characters as the air trapped in the porous surface and hydrophobic domains repel the water, leading to a very high static CA, whereas the hydrophilic domains contacting with water at the interface, though being restrained to a little fraction by the surface roughness, adhere the drop. In addition, by adding the third component, hydrophobic fluorinated polyurethane, in the blend, the formed PMMA/A-PU/F-PU blend surfaces show CA about 160 but the SA be able to rationally tune from small to large by adjusting the ratio of A-PU to F-PU. Our method provides a novel approach for controlling surface morphology, composition and corresponding surface adhesion, and may find many applications in various fields.

1) Institure of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, JAPAN

1) Graduate School of Engineering, Tohoku University, 6-6, Aoba, Aramaki-aza, Aoba-ku, Sendai, 980-8579, JAPAN

Honeycomb Films; Their Unique Structures and Surface Properties

Superhydrophobic surfaces have received great interest due to their potentials for dust-free, non-snow sticking and other functional surfaces. It is well known that surface roughness of material is important to enhance the hydrophobicity. Microporous film is one of the good candidates of superhydrophobic surfaces. Recently, we found a simple method to prepare microporous polymer films by casting polymer solution under humid conditions¹. Evaporation cooling induces the condensation of water droplets from humid atmosphere, and then, the water droplets are packed by capillary force. These water droplets work as templates of hexagonally-arranged holes on a polymer film after complete evaporation of the solvent. We prepare this "Honeycomb films" from hydrophobic polymers including fluorinated copolymers and these films show high water repellency². The honeycomb films with 300nm pores show superhydrophobicity and high transparency³. Furthermore, pincushion like films can be formed by simple peeling of the top surface of honeycomb films. These pincushion films show superhydrophobicty and high lipophobicity.

1. O. Karthaus, N. Maruyama, X. Cieren, M. Shimomura, T. Hasegawa, T. Hashimoto, Langmuir, 16(15), 6071 (2000)

^2. H. Yabu, M. Takebayashi, M. Tanaka, M. Shimomura, Langmuir, 21(8), 3235 (2005)

^3. H. Yabu, M. Shimomura, Chem. Mater., 17(21), 5231 (2005)

Wettability and Adhesion of Nano-Epoxies to UHMWPE Fibers

Ultra high molecular weight polyethylene (UHMWPE) fibers have a unique combination of outstanding mechanical, physical and chemical properties. However, UHMWPE fibers have poor wettability with most polymers. As a result, the interfacial bonding strength between the fibers and polymer matrices is very low. In our previous studies, we developed nano-matrices containing reactive graphitic nanofibers (r-GNFs) and a reactive diluent to promote the wetting and adhesion of epoxy to the fibers. In this work, the viscosity of various matrices, including a nano-epoxy and a pure epoxy, wettability and adhesion of UHMWPE fibers with different epoxy matrices were investigated. Since wettablity was influenced by the viscosity of resins in high degree, the factors affecting the viscosity of the resins were investigated experimentally. It was shown that the addition of a small amount of nanofibers into the epoxy can also reduce the viscosity. Smaller sized nanofibers reduced the viscosity more effectively. The nano-epoxy matrices have lower viscosities and much better wettability than the pure epoxy matrix as evidenced by the higher spreading rate and lower steady contact angles associated with the addition of the reactive nanofibers. The pullout tests of the UHMWPE/nano-epoxy and UHWMPE/pure epoxy were conducted, and results indicated that the adhesion of the UHMWPE fibers with the nano-epoxy is improved obviously.

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