ABSTRACTS


The following is a list of the abstracts for papers which will be presented inNINTH 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

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INDEX BY TITLE

Athanassia Athanassiou


Developing Functional Materials with Tuned Wettability and Adhesion Starting from Random Porous Substrates

Thomas Bahners



Control of Oil-wetting on Technical Textiles by Means of Photo-chemical Surface Modification and Its relevance to the Performance of Compressed Air Filters

Thomas Bahners

Some Remarks on The wetting Dynamics on Super-hydrophilic Surfaces Prepared by Photonic micro-folding

Ilker S. Bayer


Robust Superhydrophobic and Oleophobic Nanocoatings on Aluminum with Small Diffusion Flame Synthesis

I. S. Bayer1

Interaction of Liquid Droplets with C-6 Fluoroacrylic Nanofibers

Jean Berthier



Spontaneous Capillary Flows in Biotechnology: Condition for Flow Onset and Dynamics Aspects

Daniel J. Burnett

Determining Surface Energy Heterogeneity of Various Materials

Sung Kwon Cho

Cheerios Effects Modulated by Electrowetting

Sam Clark



Using Composite Laser Engineered Surfaces and Evaporating Sessile Drops to Elucidate Receding Contact Angle and Contact Line Pinning

Luisa Coriand

Investigation of the Relationship Between Roughness and Oleophilicity

Shengfeng Cheng

Capillary Adhesion at the Nanometer Scale

Melik C. Demirel



Eco-friendly Bioelastomers for Directional Wetting and Adhesion

Angela Duparré

Flexible Manufacturing and Modeling Procedures for Adjustable Surface Roughness and Wetting Properties

Frank M. Etzler


The Role of Surface Free Energy in Determining The Tensile Strength of Tablets

Kevin Golovin



Transparent Superomniphobic Surfaces

Aritra Ghosh

High-rate, Pumpless Transport of Liquids on Wettability-patterned Surfaces

Savvas G Hatzikiriakos



Contact Angle Hysteresis on Superhydrophobic Substrates: Experiments and Modelling

Dennis W. Hess



Modification of Paper/Cellulose Surfaces to Control Fluid Wetting and Adhesion

Nachiketa Janardan

Sliding of Non-circular Drops

H. Jennissen



Advances in Hyperhydrophilic Surfac Studies es, Their Characterization by Imaginary Contact Angles and First Preclinical

Lei Jiang



Bioinspired Smart Surface with Supper Wettability

Youhua Jiang


Contact Angle Hysteresis and Depinning Force on Hydrophobic Porous Surfaces

Anne Kietzig;

Splashing Behaviours of Droplets in Oblique Impacts on Textured Surfaces

Sai Kobaku



Surfaces with Patterned Wettability and their Applications

Jonathan Lawrence

Laser Wettability Characteristics Modification and the Effects Thereof on in Vitro Mesenchymal Stem Cell Response

Constantine M. Megaridis

Controlling Droplet Impact Outcome with Wettability-engineered Surfaces

Athanasios Milionis



Biodegradable Superhydrophobic Nanocomposites

Ian Morrison

Spreading Pressures, Disjoining Pressures, and the Contact Angle

Carlos Noyes


Superhydrophobic Electrolytic Heat Transfer Networks

Muhammad Osman



Solid-Liquid Interactions in Self-Cleaning Surface Mechanisms

Ridvan Ozbay



Bubble Adhesions on Surfaces of Various Wettabilities: Effect of Bubble Volumes

Chunlei Wang

Unexpect Hydrophobicity and Hydrophilicity Due to the Surface Morphology

Miguel A. RodrÍguez-Valverde

New Advances in the Measurement of the Most-stable Contact Angle

Hernando S. Salapare III

Plasma-treatment of Neptune Grass (Posidonia oceanica) to Achieve Superhydrophilic Properties

M. A. Sarshar


Analytical Models of Depinning Force of Evaporating Droplets on Superhydrophobic Surfaces

Guosheng Shi

Unexpected Hydrophilicity Due Ion-Pi Interaction

Konrad Terpiłowski


Wettability of Modified Silica Layers Deposited on Glass Support

David Waugh



Generic Parameters Governing the Wettability Characteristics of Polymeric Materials

Thomas Willers

Why Test Inks Cannot Tell the Full Truth about Surface Free Energy: An Experimental Study Comparing Dyne Inks with Contact-angle Measurements

Tak-Sing Wong


Self-Cleaning Characteristics of Slippery Liquid-Infused Porous Surfaces (SLIPS)

W. Xu

Transportation of a Microdroplet at Ultra-low Voltages by Tunable Wetting on Conjugated Polymer Electrodes

Xianmin Xu

Mathematical Understandings of Contact Angle Hysteresis




Athanassia Athanassiou, Despina Fragouli, Elisa Mele and Ilker Bayer;

Smart Materials Group, Nanophysics, Istituto Italiano di Tecnologia, Genoa, Italy


Developing Functional Materials with Tuned Wettability and Adhesion Starting from Random Porous Substrates


Starting from random porous materials, like foams, membranes and fibrous mats, and by changing their wettability characteristics we develop novel materials with specific functionalities. Some of the most recent developments of our group in this field will be discussed. In particular, hygroscopic cellulose fibers that turn into hydrophobic impermeable substrates and polymeric nanofibrous mats with water repellent or antifogging properties will be presented. There will be also demonstrated polymeric foams with tunable water permeability, between totally impermeable and totally water absorbing, to be used in the cleaning of polluted waters. Furthermore, porous polymeric membranes with induced superhydrophobic and superoleophilic character for oil-water emulsions separation will also be shown.


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Thomas Bahners1, Wolfgang MÖlter-Siemens2, Stefan Haep2 and Jochen S. Gutmann1,3


1) Deutsches Textilforschungszentrum Nord-West gGmbH (DTNW),

Adlerstr. 1, 47798 Krefeld, GERMANY


2) Institut fÜr Energie- und Umwelttechnik e.V. (IUTA), Bliersheimer Str. 60, 47229 Duisburg, GERMANY


3) UniversitÄt Duisburg-Essen, Physikalische Chemie and CENIDE,

UniversitÄtsstr. 2, 45141 Essen, GERMANY


Control of Oil-wetting on Technical Textiles by Means of Photo-chemical Surface Modification and its Relevance to the Performance of Compressed Air Filters


A two-step process comprising a surface roughening step by excimer laser irradiation and a post-treatment by photo-grafting to decrease the surface free energy was employed to increase the oil repellence of technical fabrics made of PET. The modification was designed to improve the performance of multi-layer filters for compressed air filtration, in which the fabrics served to remove, i.e. drain, oil separated from the air stream. In detail, the fibers surfaces were roughened by applying several laser pulses at a wavelength of 248 nm and subsequently photo-grafted with 1H,1H,2H,2H-perfluoro-decyl acrylate (PPFDA). The oil wetting behavior was increased by the treatments from full wetting on the as-received fabrics to highly repellent with oil contact angles of (131 + 7)̊. On surfaces in the latter state, oil droplets did not spread or penetrate even after one day. The grafting of PPFDA alone without any surface roughening yielded an oil contact angle of (97 + 11)̊. However, the droplet completely penetrated the fabric over a period of one day. The drainage performance was characterized by recording the pressure drop over a two-layer model filter as a function of time. The results proved the potential of the treatment, which reduced the flow resistance after one hour operation by approximately 25 %.


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Thomas Bahners1, Lutz Prager2 and Jochen S. Gutmann1,3


1) Deutsches Textilforschungszentrum Nord-West gGmbH (DTNW), Adlerstr. 1, 47798 Krefeld, GERMANY


2) Leibniz-Institut fÜr OberflÄchenmodifizierung e.V. (IOM), Permoserstr. 15, 04318 Leipzig, GERMANY


3) UniversitÄt Duisburg-Essen, Physikalische Chemie and CENIDE, UniversitÄtsstr. 2, 45141 Essen, GERMANY


Wetting Dynamics on Super-hydrophilic Surfaces Prepared by Photonic Micro-folding


The wetting dynamic on micro-rough and perfectly wetting – super-hydrophilic – acrylates was studied. These surfaces were achieved by coating polymer films made of poly(ethyleneterephthalate) (PET) with a hydrophilic acrylate based on hydroxypropylacrylate and polyethylenglycolmonoacrylate, which was then cured and micro-roughened by photonic micro-folding. The high transparency of the thin acrylate layers and polymer films allowed to record the spreading of an applied water droplet through the film samples. Subsequently, the dynamic radius of the spreading pattern rc(t) was determined from the video recording. Various models for the wetting dynamics of super-hydrophilic surfaces, namely Tanner’s law and a roughness-modified derivation published by McHale et al. in 2009, were then compared to the experimental results. Basically, the development of rc(t) in time was found to be in good agreement with McHale’s model. Data analysis showed, however, that the initial phase of the spreading, i.e. for t< 1 s, was not predicted well. This differing behavior relates well to a theory published by Cazabat and Cohen Stuart, who proposed that, on rough surfaces, spreading follows a power law in three time regimes. In this model, the (very) initial spreading is expected to be similar to the spreading on a smooth surface.


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Ilker S. Bayer; NanoPhysics, Italian Institute of Technology (IIT) Via Morego, 30 16163 Genova, ITALY


Robust Superhydrophobic and Oleophobic Nanocoatings on Aluminum with Small Diffusion Flame Synthesis


(Abstract not yet available)


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A. Davis1, E. Mele1, I. S. Bayer1, A. Athanassiou1 and R. Cingolani2


1) Smart Materials, Nanophysics, Istituto Italiano di Tecnologia, 16163, Genova, ITALY.

 

2) Central Labs, Istituto Italiano di Tecnologia, 16163, Genova, ITALY.


Interaction of Liquid Droplets with C-6 Fluoroacrylic Nanofibers


Fluoroacrylic polymer-based coatings are of high interest because of their unique surface properties, such as exceedingly low surface energy, low friction coefficients, repellency to both oil and water, and relatively low permeability to most gases. Among them, perfluoroalkyl ethyl methacrylate copolymers have been characterized for water as well as oil repellency applications. Due to environmental concerns many applications of fluoroacrylic polymers rely on aqueous suspensions. In addition, there are environmental concerns about the allowable length (e.g., molecular weight, C-8 chemistry) of the perfluoroalkyl group because of adverse bioaccumulation rates. The U.S. Envrionmental Protection Agency (EPA) has raised concerns over chemicals that can break down into perfluorinated acids (PFAs). One way to generate liquid repellent surfaces composed of nanofiber networks is to use the technique of electrospinning. However, water dispersions of fluoropolymers cannot be electrospun as they are not polymer solutions in reality but rather micellar polymer particle dispersions. In this work, we overcome this problem by extracting the fluoroacrylic resin in commercial aqueous fluoroacrylic dispersion (Capstone ST-100, DuPont USA) by coagulating, isolating and re-dispersing in acetone solutions. After proper concentration adjustment, nanofibers can be spun with a standard electrospinning setup. Electrospun nanofiber mats of Capstone ST-100 are oleo- and solvent-phobic. Their morphology mimics coral reef-like features. Moreover, the fluoropolymer solutions can be blended with cellulosic polymer solutions in acetone allowing us to fabricate polymer blend nanofibers. These polymer blend nanofibers demonstrate an extraordinary ability to encapsulate water droplets forming rather robust liquid marbles.


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Jean Berthier; CEA-Leti, Department of Biotechnology, Bat. 42, 17, Avenue des Martyrs, 38054 Grenoble, FRANCE


Spontaneous Capillary Flows in Biotechnology: Condition for Flow Onset and Dynamics Aspects


Email : jean.berthier@cea.fr


(Abstract not yet available)


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Daniel J. Burnett1, Armando R. Garcia1, Anett Kondor2, Majid Naderi2, and Manaswini Acharya2


1) Surface Measurement Systems Limited, 2125 28th Street SW, Suite 1, llentown, PA 18103, USA


2) Surface Measurement Systems Limited, 5 Wharfside, Rosemont Road, Alperton, London, UK


Determining Surface Energy Heterogeneity of Various Materials


Most real-world solids are energetically heterogeneous. This heterogeneity could be due to different crystal faces, co-crystals, impurities, defect sites, amorphous regions, composites, or co-processed mixtures of materials. Therefore, it is often difficult or even misleading to characterize the surface energy of these materials with a single value. Recent advances in Inverse Gas Chromatography (IGC) theory and applications have developed new methods for determining surface energy distributions for solids using IGC.1,2 This approach allows for the determination of surface energy values at defined specific surface coverages and determination of surface energy profiles. These measurements more accurately represent the anisotropic nature of most solids.


This presentation will discuss several studies where surface energy distributions have been determined. For instance, the affects of processing route on the surface properties of partially amorphous drugs has been investigated. Studies on oxidized carbon fibers indicate trends in surface polarity with oxygen to carbon ratios. Further, surface energy values for carbon based filtration media were correlated to wettability.


References


1. Thielmann, F., Burnett, D.J., and Heng, J.Y.Y., Drug Development and Industrial Pharmacy, 33 (2007) 1240-1253.

2. YlÄ-MÄihÄnemi, P.P., Heng, J.Y.Y., Thielmann, F., and Williams, D.R., Langmuir, 24 (2008) 9551-9557.


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Junqi Yuan and Sung Kwon Cho, University of Pittsburgh, Pittsburgh, PA 15261, USA


Cheerios Effects and their Modulation by Electrowetting


Cheerios effect is a common phenomenon in which small floating objects are either attracted or repelled by the sidewall due to capillary interactions. The attractive and repulsive behaviors between floating objects and sidewalls are highly dependent on the properties (hydrophobicity, density, etc.) of floating objects and sidewalls. First, we present how this phenomenon responds to the different properties including the density and hydrophobicity of the floating objects and hydrophobicity of sidewalls. Then, the Cheerios effect is combined with EWOD (electrowetting on dielectric) in order to actively manipulate floating objects. We embed EWOD electrodes in the sidewall. In response to the external voltage applied to the electrodes on the sidewalls, the surfaces of the sidewalls can be switched between hydrophobic and hydrophilic states, resulting in interface distortions and thus lateral forces on floating objects. By sequentially applying the external voltages in the multiple electrodes and carefully controlling the time step, we can propel and rotate floating objects continuously. In this talk, detailed results along with effects of many parameters will be presented and discussed.



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Shengfeng Cheng1 and Mark O. Robbins2


1) Department of Physics, Virginia Polytechnic Institute_and State University, Blacksburg, Virginia 24061, USA


2) Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA


Capillary Adhesion at the Nanometer Scale


Molecular dynamics simulations are used to study the capillary adhesion from a nonvolatile liquid meniscus between a spherical tip and a flat substrate. The atomic structure of the tip, the tip radius, the contact angles of the liquid on the two surfaces, and the volume of the liquid bridge are varied. The capillary force between the tip and substrate is calculated as a function of their separation h. The force agrees with continuum predictions for h down to ~ 5 to 10nm. At smaller h, the force tends to be less attractive than predicted and has strong oscillations. This oscillatory component of the capillary force is completely missed in the continuum theory, which only includes contributions from the surface tension around the circumference of the meniscus and the pressure difference over the cross section of the meniscus. The oscillation is due to molecular layering of the liquid confined in the narrow gap between the tip and substrate. This effect is most pronounced for large tip radii and/or smooth surfaces. The other two components considered by the continuum theory are also identified. The surface tension term, as well as the meniscus shape, is accurately described by the continuum prediction for h down to ~ 1 nm, but the capillary pressure term is always more positive than the corresponding continuum result. This shift in the capillary pressure reduces the average adhesion by a factor as large as 2 from its continuum value and is found to be due to an anisotropy in the pressure tensor. The cross-sectional component is consistent with the capillary pressure predicted by the continuum theory (i.e., the Young-Laplace equation), but the normal pressure that determines the capillary force is always more positive than the continuum counterpart.



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S. J. Clark, D. G. Waugh and J. Lawrence; Laser and Photonics Engineering Group, School of Engineering University of Lincoln, Brayford Pool, Lincoln, LN6 7TS, UK


Using Composite Laser Engineered Surfaces and Evaporating Sessile Drops to Elucidate Receding Contact Angle and Contact Line Pinning


— A systematic study of the role of surface roughness when applied to the central region within the initial contact line, under evaporating sessile drops, is presented. This study is based upon recent derivations and experimental studies exploring the applicability of the Cassie-Baxter and Wenzel equations, the relationship between contact angle hysteresis and contact line pinning and of evaporating sessile drops. Composite roughened surfaces have been prepared using CO2 laser marking upon relatively smooth polyethylene (PE). Surfaces were prepared upon which the roughness and location upon which the surface treatment applied was carefully controlled in order to the preserve the axisymmetry of the deposited sessile drops. The observed contact angle of evaporating sessile drops with a contact line contracting over regions with varying roughness was carried out using axisymmetric drop shape analysis - profile (ADSA-P). The evaporation of the deposited sessile drops observed was achieved through the careful control of the temperature within a confined chamber, utilising the peltier effect. Attention was paid to endeavour to maintain constant humidity. Insights have been presented into the behaviour of the dynamic contact lines of evaporating sessile drops at interfaces in surface roughness.



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Luisa Coriand1, Markus Rettenmayr2, and Angela DuparrÉ1

 

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


2 Friedrich-Schiller-University, Otto Schott Institute of Materials Research, LÖbdergraben 32, 07743 Jena, GERMANY


Investigation of the Relationship Between Roughness and Oleophilicity


First approaches and results are presented to extend our measurement and analysis methodology for hydrophobic and hydrophilic wetting systems to oleophilic surfaces. The wetting properties of oil on engineering surfaces are of great importance for the friction and wear resistance of tribological systems. This research focuses on achieving complete wettability (contact angle < 5¡) of oil through functional surfaces using specific surface roughnesses.


To investigate the relationship between the surface roughness and olephilic wetting behavior, robust roughness analysis and apparent contact angle measurements for different system temperatures are performed. The characterization of the roughness structures bases on Power Spectral Density (PSD) functions determined from AFM and WLI topography data and subsequent data reduction. Furthermore, our well-established wetting analysis methods are transferred, optimized, and extended with respect to the specific wetting situation with oil as liquid phase.

 

Examples are given for oleophilic structured steel substrates.


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Melik C. Demirel; Pennsylvania State University,212 EES Bldg, University Park, PA, 16802


Eco-friendly Bioelastomers for Directional Wetting and Adhesion


Materials properties of bio-elastomers extracted from biological samples could vary heavily between the species within the same genus due to the differences in structure and composition. The gain or loss of materials properties (such as wet and dry adhesion) between different species shed light into not only the molecular structure but also the integration of the hierarchy of systems that serves at morphological length scales. Therefore understanding the functional transitions of the biomimetic systems help us to design, fabricate and synthesize materials resilient to environmental factors, as well as eco-friendly advanced materials for novel asymmetric wetting, and adhesion properties


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Angela Duparré; Fraunhofer Institute for Applied Optics & Precision Engineering, Albert-Einstein-Straße 7, D-07745 Jena,GERMANY


Flexible Manufacturing and Modeling Procedures for Adjustable Surface Roughness and Wetting Properties


During the past decade, surfaces with specific functional features have gained continuously increasing attention. The most prominent examples are wetting phenomena like hydrophobicity and hydrophilicity at different degrees, all the way up to super-hydrophobic and -hydrophilic properties. For a successful technology to manufacture such surfaces, the knowledge of the main relations between their structural and functional properties plays a key role. In this talk, an approach on how to acquire that knowledge will be presented. This approach is based on a comprehensive methodology comprising advanced roughness characterization techniques, functional analysis, modelling procedures, and systematic model samples series. The latter can be realized through thin films with flexibly graded roughness structures and wetting properties. Such films can be advantageously generated by sol-gel dip-coating processes with specific variation of the deposition parameters and post deposition treatment. Besides the examples of wetting phenomena, the general approach can be also extended to the study of other functionalities like e.g. haptics.


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Frank M. Etzler and Sorona Pisano, School of Pharmacy, Lake Erie College of Osteopathic Medicine, 1858 W. Grandview Blvd. , Erie, PA 16509,


Email: fetzler@lecom.edu



The Role of Surface Free Energy in Determining The Tensile Strength of Tablets


Tablets are the most common dosage form employed by the pharmaceutical industry. They are both inexpensive to produce and convenient to patients. Active pharmaceutical ingredients, particularly those incorporated into innovator company products, are new chemical substances whose chemical and physical properties are incompletely known and are sometimes present in large amounts in the manufactured products. Excipients present in the formulation can, at least partially, offset undesirable properties of active ingredient. Successful tablet formulations must, in addition to having desirable medicinal properties, must be manufacturable. In order to be manufacturable tablets must have sufficient tensile strength to survive handling, processing and packaging. In this paper a model, based on adhesion science principles is discussed that allows the tensile strength of candidate formulations to be calculated from the Ryshkewitch-Duckworth parameters of the component materials. Both the model and the Ryshkewitch-Duckworth equation suggest that tablet porosity is the principal measure of the outcome of the tableting process. Furthermore, the role of the surface free of component materials in determining the tablet tensile strength. The data suggest that material surface free energies and tablet porosity determine tablet hardness.


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Kevin Golovin; University of Michigan, Materials Science & Engineering, 2800 Plymouth Rd., Ann Arbor, Michigan 48109


Transparent Superomniphobic Surfaces


(Abstract not yet available)


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Aritra Ghosh,1 Ranjan Ganguly,1,2 Constantine M. Megaridis1


1) Micro/Nanoscale Fluid Transport Laboratory, Department of Mechanical & Industrial Engineering, University of Illinois at Chicago, IL 60607, USA


2) Department of Power Engineering, Jadavpur University, Kolkata 700098, INDIA


High-rate, Pumpless Transport of Liquids on Wettability-patterned Surfaces


Achieving controlled and rapid transport of liquids on open substrates is important for several practical applications, ranging from phase-change heat transfer to rapid chip cooling and lab-on-chip devices. We use facile, scalable surface wettability engineering approaches to fabricate patterned substrates that comprise strategically laid superhydrophilic tracks on superhydrophobic backgrounds. Spatial contrast of surface energy on the patterned substrates provides fast actuation of microliter droplets through hemiwicking and Laplace pressure-driven flow. Proof-of-concept demonstration of rapid and pumpless transport, splitting, merging and metered dispensing of liquid droplets on patterned substrates is provided. The design facilitates transport against gravity, thus making operation of 3-D devices feasible. Suitability of the design for different microfluidic and microscale thermophysical applications is also discussed.



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


Contact Angle Hysteresis on Superhydrophobic Substrates: Experiments and Modelling


Micro/nano-patterned superhydrophobic morphologies have been manufactured on stainless steel using a laser irradiation technique. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nanostructures. These microstructure were analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium contact angle (CA) and contact angle hysteresis (CAH). The model is designed to predict the contact angle and contact angle hysteresis on micro/nano structures with non-flattened top asperities. The effects of the geometrical details on maximizing the superhydrophobicity of the nano-patterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters which may lead to lotus effect (high CA>150o and low CAH<10o) or petal effect (high CA>150o and high CAH>>10o).



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Dennis W. Hess; School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100


Modification of Paper/Cellulose Surfaces to Control Fluid Wetting and Adhesion


(Abstract not yet available)


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Nachiketa Janardan and Mahesh V. Panchagnula*; Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai – 600036 INDIA


*Corresponding author’s e-mail address – mvp@iitm.ac.in


Sliding of Non-circular Drops


We present a study on the onset of motion of non-circular drops on an inclined plane. The drops were of constant volume and nearly the same perimeter. However, we varied the orientation of the drop to the direction of motion. Moving and Sliding angles were measured for the drops and the results were tabulated. When the major axis of the drop is oriented in the direction of motion, the profile of a drop as viewed from the camera resembles a hydrophilic drop, that is, the front and back edges have initial contact angles close to the receding angle of the surface. Thus the sliding behavior of such a drop is similar to that of a hydrophilic drop in that the back edge starts moving first and the front edge moves later. Similarly, when the minor axis is in the direction of motion, the drop profile resembles a hydrophobic drop with suitably similar behavior. It is seen that two drops with identical wetted areas can demonstrate radically different sliding behavior due to the difference in their orientation.


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H. Jennissen; Institut fÜr Physiologische Chemie, UniversitÄt Duisburg-Essen, UniversitÄtsklinikum Essen, Hufelandstr. 55, D-45122 Essen GERMANY


Advances in Hyperhydrophilic Surfaces, Their Characterization by Imaginary Contact Angles and First Preclinical Studies


(ABSTRACT NOT YET AVAILABLE)


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Lei Jiang; Institute of Chemistry, Chinese Academy of Sciences,No.2, 1st North Street, Zhongguancun, Beijing, 100080 P.R.CHINA


Bioinspired Smart Surface with Supper Wettability


(Abstract not yet available)


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

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


Contact Angle Hysteresis and Depinning Force on Hydrophobic Porous Surfaces


Recently there were several works reporting that the contact angle hysteresis and pinning/adhesion force on heterogeneous surfaces such as micro/nano-patterned superhydrophobic surfaces should be determined by the dynamics of effective contact line at the droplet boundary rather than the effective contact area. However, such studies were mostly performed with pillar-patterned surfaces and the understanding of porous surfaces is limited. In this study, the advancing and receding angles of a sessile droplet on hydrophobic micro-porous surfaces of systematically varied dimensions are measured to find out the direct correlation between the dynamics of effective contact line and the contact angle hysteresis as well as the depinning force. The results are also compared to those based on effective contact area and those of micro-pillared surfaces.


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Damon Aboud and Anne Kietzig; Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec, CANADA


Splashing Behaviours of Droplets in Oblique Impacts on Textured Surfaces


The splashing behaviour of a droplet on a flat surface is governed not only by the trajectory of the collision, but also by surface properties such as roughness and surface chemistry. Droplet impacts on stationary surfaces at normal impact angles are already well understood, however, this is rarely the case for droplets colliding with surfaces in real engineering applications. In contrast, the splashing behaviours of droplets on angled, moving surfaces are not well understood, especially on textured surfaces. In this work, droplet impact experiments are performed with water droplets on angled, fast-moving surfaces composed of smooth, rough, and laser-treated aluminum and PTFE. These experiments provide a comprehensive view of the effect of the surface on droplet splashing.


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Sai Kobaku; University of Michigan, Macromolecular Science & Engineering, 2800 Plymouth Road, Ann Arbor, MI 48105


Surfaces with Patterned Wettability and their Applications


Surfaces with patterned wettability have well-defined domains with contrast in their surface energy. Such patterned surfaces have many potential applications in fog harvesting and liquid transport, microchannels and microreactors, enhanced condensation and boiling heat transfer, and the selective deposition of thin films. However, the majority of patterned surfaces developed thus far exhibit extreme wettability contrast only with high surface tension liquids such as water (surface tension,γlv = 72.1 mN m-1), thereby limiting the applications of such surfaces mostly to surfactant-free aqueous systems. In this work, we have developed first-ever patterned superomniphobic-superomniphilic surfaces that exhibit stark contrast in wettability with a wide range of polar and non-polar liquids. Using such patterned surfaces, we demonstrate the site-selective self-assembly of both high as well as very low surface tension liquids upon dipping and spraying. We have also demonstrated that here developed patterned surfaces can be applied to enhance both condensation and boiling heat transfer with low surface tension liquids. Further, we have utilized these patterned surfaces for site-selective self-assembly of a wide variety of polymers films and microparticles in different shapes and sizes.


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J. Lawrence1, C.W. Chan2 and D.G. Waugh1


1) Laser and Photonics Engineering Group, School of Engineering, University of Lincoln, Brayford Pool, Lincoln, LN6 7TS, UK


2) School of Mechanical and Aerospace Engineering, Queen's University Belfast, UK

Laser Wettability Characteristics Modification and the Effects Thereof on in Vitro Mesenchymal Stem Cell Response


Only the uppermost surface layers of a biomaterial are in direct physicochemical contact with the biological environment. The common belief is that no more can be done to improve a biomaterial’s performance by working from the surface into the bulk; it is now time to concentrate on the surface to body. This is so for stem cells, which will be foremost in the future of regenerative medicine as only they can grow into new tissue or body parts. But with surface properties often compromised for the sake of bulk properties, the industry is left with surfaces that do not support sufficiently the level of bioactivity required. This leads to clinical complications or even failure. Wettability characteristics are among the chief drivers for cell response and laser surface treatment offers a unique means of promoting cell response on the surface of biomaterials, whilst retaining the bulk properties, through modification of wettability characteristics to produce a biomimetic surface.


CO2 laser wettability characteristics modification to produce a biomimetic surface on a NiTi alloy was examined in vitro with mesenchymal stem cells (MSCs). Improved biocompatibility of the NiTi alloy surface following CO2 laser wettability characteristics modification was evidenced by higher cell attachment and viability over an untreated surface. What is more, it was found possible to modulate the cellular responses of the MSCs through control of the laser operating parameters to obtain biomimetic surfaces with wettability characteristics optimized for triggering differentiation. Modifying wettability characteristics in this way is a highly attractive means of estimating and determining the biofunctionality of a biomaterial and shows that the generation of biomimetic surfaces using laser wettability characteristics modification provides an in vitro platform on which to deposit and grow stem cells for either the development of implants or to reconstitute functional tissue.



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Constantine M. Megaridis,1 Thomas M. Schutzius,1,2 Gustav Graeber,3Mohamed Elsharkawy1


1) Micro/Nanoscale Fluid Transport Laboratory

Department of Mechanical & Industrial Engineering

University of Illinois at Chicago, IL 60607, USA


2) Department of Mechanical and Process Engineering

Swiss Federal Institute of Technology

8092 Zurich, SWITZERLAND


3) Department of Mechanical Engineering, RWTH Aachen, 52072 Aachen, GERMANY


Controlling Droplet Impact Outcome with Wettability-engineered Surfaces


Fluid dynamic transport during droplet impact on solid surfaces has been studied for decades. More recent work has concentrated on surfaces with extreme wettability (superhydrophilic, superhydrophobic). In this study, we report experimental results using surfaces with spatially-patterned domains of different wettability. Such surfaces are implemented for converting droplets from spheres to complex shapes (e.g. annuli or squares). The procedure harnesses the naturally occurring contact line pinning mechanisms at sharp wettability changes to influence droplet impact outcome, or even mobilize the fluid asymmetrically during orthogonal impact. The study offers a new approach to shape impacting droplet microvolumes, with ramifications in surface microfluidics or fluid-assisted templating applications.


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Athanasios Milionis1,2, Ilker S. Bayer1,2, Roberta Ruffilli3, Eric Loth1 and Athanassia Athanassiou4

 

1 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville (VA), USA

 

2) Nanophysics, Istituto Italiano di Tecnologia, Genova, ITALY


3) Nanochemistry, Istituto Italiano di Tecnologia, Genova, ITALY


4) Center for Biomolecular Nanotechnologies, Italian Institute of Technology@UniLe, Via Barsanti, Arnesano (Lecce), ITALY


Biodegradable Superhydrophobic Nanocomposites


We report on the synthesis and surface properties of biodegradable, superhydrophobic coatings composed of a biopolymer and hydrophobic fumed silica. A simple spraying setup is used to uniformly coat various types of substrates like paper, metals and semiconductors. By varying the concentration of biopolymer to fumed silica the wetting properties can be controlled, transforming gradually the inherently hydrophilic biopolymer into a superhydrophobic biodegradable coating with water contact angle > 150̊ and roll-off angles down to 1̊. A thermal treatment for 30 min at 130̊ is found to further improve the performance. Moreover, the coatings are mechanically resistant since they remain adhered to the sprayed surface and maintain their properties after successive folding tests. A final spraying step of a very thin, almost transparent coating with an aqueous fluorochemical dispersion transform the surfaces to superoleophobic with oil contact angle > 150̊ and roll-off angle 15̊. Investigation of the surface topography with Scanning Electron Microscopy unveiled micro- and nano-rough sponge-like features that are responsible for the extreme wetting characteristics. Such a simple inexpensive and fast, material system based on commercially available ingredients can further the development of new generation green superhydrophobic materials.


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Ian Morrison; SEAS, Harvard University, Cambridge, MA


Spreading Pressures, Disjoining Pressures, and the Contact Angle


A sessile drop on a solid surface is in equilibrium with the spreading pressure of the adsorbed film. The disjoining pressure, analyzed in the language of de Gennes, accounts for the equilibrium between the sessile drop and the adsorbed film. The spontaneous formation and subsequent equilibrium of a sessile drop and an adsorbed film is the consequence of the fact that the extended liquid film is unstable, that is, the thin film undergoes a phase change. Therefore the adsorbed film and sessile drops are described by the minimization of the free energy of the thin, extended film and produces an equation that relates the properties of the thick film with properties of the thin film, giving an expression for the contact angle. Because the spreading pressure of the thin film is easily calculated from the gas adsorption isotherm, contact angles can be determined for submicron particles, for which contact a are not directly measurable.


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Carlos Noyes1, Athanasios Milionis1, Eric Loth1, Ilker S. Bayer 1,2


1 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville (VA), United States


2 Nanophysics, Istituto Italiano di Tecnologia, Genova, Italy


Superhydrophobic Electrolytic Heat Transfer Networks


Heat transfer networks, such as honeycomb surfaces and interrupted plates, are of great importance in applications for energy storage by liquid piston-driven isothermal air compression. However, as the liquid piston passes over the heat transfer elements, it may lead to residual water drops that create blockage and reduce heart transfer performance. Therefore, we investigate different methods for reducing the mass of retained water in 3D heat transfer networks by rendering their surface superhydrophobic and applying electrolysis in the case of metallic elements. The networks under investigation include 3D-printed plastic meshes, machined aluminum honeycombs and porous aluminum foams. A dip-coating strategy is followed to make the heat transfer networks superhydrophobic with a dispersion composed of Capstone ST-200 (DuPont) and hydrophobically modified fumed silica dispersed in butyl acetate. After this treatment, the network surfaces exhibit water contact angles > 150̊. The water mass retained after immersing the networks in water for 1 sec was measured and was reduced by 45% for the dip-coated surfaces compared to the uncoated surfaces. In the case of the metallic networks, the reduction reached 55% when combined with electrolysis electrolysis using a 1 V bias which caused the formation of micro-bubbles across the entire surface. Such approaches can significantly improve the functionality of the abovementioned energy storage systems.


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Muhammad Osman and Roger A. Sauer; Aachen Institute for Advanced Study in Computational Engineering Science (AICES), RWTH Aachen University, Templergraben 55, 52056 Aachen, GERMANY


Solid-Liquid Interactions in Self-Cleaning Surface Mechanisms


Based on a finite element (FE) model, we study the self-cleaning effect, also known as the lotus effect, which is observed on hydrophobic surfaces. The interaction between these surfaces, liquid droplets, and pollutant particles is investigated through a force analysis. Some forces such as the capillary force and the contact line force, require numerical treatment of the liquid droplet membrane deformation, governed by the Young-Laplace equation. Based on this analysis, we compute the net force governing the behaviour of a particle in contact with a liquid droplet. This work provides answers to the following questions: In a quasi-static framework, does the self-cleaning mechanism work for given surface and droplet parameters? I.e: would a particle be lifted off by the water droplet or not? How do the model parameters affect the net force acting on the particle? The parameters considered in this study are: volume and density of the liquid droplet, size, density and contact angle of the pollutant particle, and roughness and contact angle of the substrate surface.


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Ridvan Ozbay1, Ali Kibar2, and Chang-Hwan Choi1


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


2) Department of Mechanical and Material Technologies, Kocaeli University, Kocaeli 41380, TURKEY


Bubble Adhesions on Surfaces of Various Wettabilities: Effect of Bubble Volumes


Experimental analyses of the adhesion forces of air bubbles on hydrophobic, hydrophilic, and superhydrophilic surfaces were performed. A Teflon sheet, a bare silicon substrate, and a micropillared silicon substrate with an apparent contact angle of a sessile water droplet of 110̊, 35̊, and 4̊ were used as a hydrophobic, a hydrophilic, and a superhydrophilic surface, respectively. Each substrate was immersed in water, and an air bubble was injected below to the lower surface using micropipette. In order to measure the adhesion force of a bubble on each surface, the substrate was gradually inclined until the bubble started to slide up. The profile of the bubble was captured by the camera continuously while the surface was gradually inclined. The volumes of the bubbles were systematically varied in the range of 7-40 uL to investigate the effect of the volume of an air bubble on the sliding angle and the adhesion force. The results show that the difference of the maximum and minimum contact angles at the uphill (advancing) and downhill (receding) sides and hence the adhesion force significantly decrease with an increase of the bubble volume in case of the superhydrophilic surface, compared to the cases of the hydrophilic and hydrophobic ones.


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


Unexpect Hydrophobicity and Hydrophilicity Due to the Surface Morphology


The surface wetting behavior of water, usually named hydrophobicity/hydrophilicity, plays a key role in various processes, including the aqueous solvation process, self-assemble of amphiphilic molecules and protein folding. Conventionally, the surfaces with polar molecules or groups are usually regarded as hydrophilic. Here, I will give a talk that the wetting property also critically depends on the surface morphology. (1) We observed the phenomenon “ordered water monolayer does not completely wet water” at room temperatures on a simple model surface based on MD simulations. This could be attributed the perfect match between the water molecules and the surface charge patterns, resulting in the hexagonal ordered water monolayer. This ordered water structure reduced the possibility of hydrogen bond formation between the ordered water and the molecules above this monolayer. Recently, German and Australian scientists experimentally found the similar phenomenon of “ordered water monolayer does not completely wet water” on sapphire c-plane surface and self-assemble monolayer (SAM) surface with the terminal of -COOH. The similar phenomenon has also been observed on real surfaces, such as the talc, hydroxylated Al2O3, hydroxylated SiO2 and Pt surfaces, based on MD simulations. (2) We proposed that the polar surface with charge dipoles might be hydrophobic when the charge dipole length was smaller than a critical value. This unexpected observation resulted from the mismatch between the water molecules and charge dipoles on the solid surface, where the steric exclusion effect (crowded effect) between water molecules prevented those hydrogen atoms of water molecules from staying very close to the negative charge and those oxygen atoms of water molecules from staying very close to the positive charge, reducing the interactions between the water molecules and the charge dipoles. Interestingly, the hydrophobic behaviour due to small lattice length, which result in small charge dipoles, has been observed experimentally recently.


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Hernando S. Salapare III1,* Ma. Gregoria Joanne P. Tiquio2, and Henry J. Ramos1


1) Plasma Physics Laboratory, National Institute of Physics, College of Science, University of the Philippines, Diliman, Quezon City 1101, philippines


2) UniversitÉ de Nice-Sophia Antipolis, EA 4228 ECOMERS, Parc Valrose, 06108 Nice Cedex 2, france


*Corresponding Author. E-mail: hssalapare@up.edu.ph

Plasma-treatment of Neptune Grass (Posidonia oceanica) to Achieve Superhydrophilic Properties

Neptune Grass (Posidonia oceanica) samples were treated using argon and oxygen plasma at varying plasma energies that ranges from 6 kJ to 180 kJ. The characterizations done on the samples were weight loss analysis, wettability studies, surface roughness measurements, and determination of the surface chemical functionalities. Greater weight loss was observed on the oxygen plasma treatment than the argon plasma treatment. Superhydrophilic surface properties (q < 5̊ within 1 second of spreading) were achieved at high-energy argon-plasma treatment and low-energy oxygen- plasma treatments. The surface roughness increased for the high-energy argon-plasma treatments; however, opposite trend was seen for the oxygen-plasma treatments. The –CH2 groups and the aliphatic C-H groups were absent from the FT-IR spectra of the superhydrophilic samples. Superhydrophilic surfaces were achieved mainly from the change in the surface roughness and the change in the chemical functionalities of the samples after the plasma treatment.


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M. A. Sarshar, Y. Jiang, W. Xu, and C.-H. Choi; Department of Mechanical Engineering, Stevens Institute of Technology, New Jersey, USA

Analytical Models of Depinning Force of Evaporating Droplets on Superhydrophobic Surfaces

An analytical model for predicting the depinning force of an evaporating droplet on superhydrophobic surfaces is studied and compared with the existing experimental results. Two main parameters are attributed to constitute the force: one is a solid fraction which is associated with the kinetic effect of a solid surface touched by water, and the other is the effective three-phase contact line (length) around a droplet boundary which is related to the dynamic effect of a receding droplet. A depinning force can then be divided into two components, including the force raised from wetting energy (kinetic effect) and the force caused by the change in the shape of meniscus as it deforms in the contact line (dynamic effect). These two components should be added together since both act at the same time in depinning. The proposed analytical model and experimental results show a good agreement. The derived formula suggests that as the effective contact line for a surface structure becomes smaller (e.g., with an increase of the periodicity of a pillar array with a constant diameter), the magnitude of the depinning force deviates from the linear relationship previously reported and decreases in a parabolic way with respect to the effective contact line, which is due to the kinetic effect of the wetting energy resulted from the wetted area of surface structures.

 

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Guosheng Shi; Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, CHINA

 

Unexpected Hydrophilicity on Hydrophobic Carbon-Based Surfaces due to Cation-π Interactions

 

On typical carbon-based surfaces with the aromatic rings, (such as graphite, graphene and polycyclic aromatic hydrocarbons), as well known popular hydrophobic surfaces, water is known to only adsorb below an extremely low temperature. However, here, we show that an unexpected nanometer-thick aqueous water solution film (pancake) under ambient condition on hydrophobic carbon-based surface. This indicates the unexpected nanoscale hydrophilicity on hydrophobic carbon-based surfaces. More surprisingly, the pancake spontaneously display positively charged behaviour when the pancakes are obtained by simply removing aqueous from surfaces. The key to the formation of such positively-charged water solution pancakes was attributed to the cation-π interactions between the Na+ ions in the aqueous solutions and the aromatic rings on the graphite surfaces, promoting the adsorption of water molecules onto the graphite surfaces. Considering that the π electron rich structures are abundant in other carbon-based materials including biochar, air pollutants, as well as biomolecules, and other cations have similar behavior as Na+, this finding suggests that the interactions related to many popular and important surfaces may be significantly different from the existing theory and provides new insight to the control of surface wettability and interactions. The behaviours of charged and wetting change on hydrophobic aromatic rich carbon-based surface under ambient conditions may have widespread potential for dealing with water, air or soil pollution from heavy metals.

 


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Konrad Terpiłowski1, Diana Rymuszka1, Lucyna Holysz1, Elena Goncharuk2, Iryna Sulym2 and Emil Chibowski1

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

2) Chuiko Institute of Surface Chemistry, National Academy of Science of Ukraine, Kiev, UKRAINE

Wettability of Modified Silica Layers Deposited on Glass Support

The fumed silica powder used for the experiment was modified by hexamethyldisilazane [HDMS] presented during its precipitation, were applied. The silica particles were dispersed in polystyrene/chloroform solution. To increase of the silica layers adhesion the glass surface was treated by air plasma for 30 s. Then the dispersion was deposited on the glass support using a spin coater. After that the plates were dried for 24 hours in desiccator, before using them for water advancing and receding contact angles measurement by sessile droplet or tilted plate method. The apparent surface free energy of these surfaces was evaluated using the hysteresis approach. Topography of the surfaces was examined with help of optical microscopy and optical profilometry.

The water contact angles changed from 59.7̊+4.4 for surface covered by silica with 0.06 mM/g HMDS per 1 g SiO2 to 155̊+3.1 if 0.68 mM/g HMDS per 1 g SiO2 was used. The apparent surface free energy calculated from the hysteresis approach decreased from 51.3+2.8 mJ/m2 for sample with the lowest amount of HMDS to only 1.0+0.4 mJ/m2 for the most hydrophobic sample. Thus some systems with the higher amount of HDMS showed superhydrophobic effect on which the sliding angle was about 16̊+2.1.

ACKNOWLEDGEMENT

The research leading to these results has received funding from the People Programme
(Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013/under REA grant agreement n̊ PIRSES-GA-2013-612484 and and the Visegrad Fund (Contract number 51300077)


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Carmen L- Moraila-MartÍnez1, MarÍa J. Santos2, Juan A. White2, Miguel A. Cabrerizo-VÍlchez1, Miguel A. RodrÍguez- Valverde1


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

2) Department of Applied Physics, University of Salamanca, SPAIN


New Advances in the Measurement of the Most-stable Contact Angle


Equilibrium contact angle is the contact angle of the configuration of minimum free energy of the system. However, the experimental determination of equilibrium contact angles is still an open question. Instead, from an operative point of view, the most stable equilibrium configuration can be identified as the mechanically (meta)stable configuration, within the hysteresis range, with the lowest susceptibility to external mechanical stimuli [1]. In other respects, the most-stable equilibrium configuration is usually predicted from the two observable configurations corresponding to advancing and receding contact lines, following the so-called rule of the mean cosines. This rule reflects that when the system attains the most-stable configuration then the triple line should require a greater stimulus to advance or recede. Following this idea, we propose to measure the most-stable contact angle of sessile drops, without mechanical stimuli, from growing/shrinking drop experiments [2]. Once the sessile drop stops advancing but before it begins to recede, the shrinking drop is pinned. We postulate the contact angle corresponding to the arithmetic mean volume between the critical volumes just after advancing and just before receding as the most-stable contact angle. This proposal was validated with both numerical (Surface Evolver [3]) and experimental results.

[1] Equilibrium contact angle or the most-stable contact angle? F.J. Montes Ruiz-Cabello, M.A. Rodriguez-Valverde and M.A. Cabrerizo-VÍlchez. ACIS 10.1016/j.cis.2013.09.003.

[2] Contact angle hysteresis on polymer surfaces: an experimental study. F.J. Montes Ruiz-Cabello, M.A. Rodriguez-Valverde and M.A. Cabrerizo-VÍlchez. JAST, 25(16), 2011, 2039-2049.

[3] Simulation Analysis of Contact Angles and Retention Forces of Liquid, Drops on Inclined Surfaces. M. J. Santos, S. Velasco, and J. A. White. Langmuir, 2012, 28 (32), pp 11819–11826


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David Waugh; School of Engineering, University of Lincoln, Brayford Pool, Lincoln, LN6 7TS, UK


Generic Parameters Governing the Wettability Characteristics of Polymeric Materials

 

Wettability is an interesting subject which spans any discipline that takes into account any form of adhesion. As such, it is imperative to identify generic parameters that govern the wetting nature of materials. This paper makes inroads into understanding how the laser surface engineering of nylon 6,6, ultra-high molecular weight polyethylene (UHMWPE) and Poly(methyl methacrylate) (PMMA) manipulates the wettability characteristics. Infrared (IR) and ultraviolet (UV) lasers sources were employed to produce patterned surface topographies. White light interferometry (WLI) was used to characterize these laser-modified surface topographies, X-ray photoelectron spectroscopy (XPS) was used to determine surface oxygen content and a sessile drop device was used to determine wettability characteristics. The results for certain samples did not follow current, accepted wetting theory and we propose the possible presence of a mixed-state wetting regime to explain this. Using analytical regression analysis, generic equations to predict this mixed-state wetting regime and the corresponding contact angles are discussed.

 

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Thomas Willers and Ming-Jin, KRÜSS GmbH, Hamburg, GERMANY

Why Test Inks Cannot Tell the Full Truth about Surface Free Energy: An Experimental Study Comparing Dyne Inks with Contact-angle Measurements

Adhesive bonding has developed to the tool of choice if metals, plastics or other materials need to be connected. For many materials extensive pre-treatment as cleaning, surface roughening or plasma activation are applied prior to the gluing process. All these treatments have one mayor goal in common: improving the wettability of glue on surfaces. To monitor the efficiency of these processes the surface-free energy (SFE) of the substrate is measured. In many cases dyne inks are used to determine the total SFE following the assumption that a surface having a SFE value above a certain threshold is sufficiently treated for the following adhesive bonding.

However, the SFE is more than one single value and its distribution into polar and disperse constituents is essential if wetting and long term adhesion shall be characterized. In contrast to dyne inks, contact-angle measurements determine the polar and disperse contributions to the SFE.

In a thorough experimental study we determined the SFE of various materials using different types of dyne inks (yellow ethanol and blue formamide based ones) and contact-angle measurements. The investigated materials range from polymers (polyamide, polypropylene, polyethylene, polytetrafluoroethylene, polyvinyl chloride, polyethylene terephthalate), glassware, silicon wafer, mica, and graphene, to metals like aluminium. In addition, we tested some materials before and after plasma treatment. Results obtained with test inks and contact-angle measurements will be compared illustrating advantages and drawbacks of either technique. We explicitly explain why for some materials test inks and contact-angle measurements yield different results. For that purpose we determined polar and disperse parts of test inks. Finally, we give an example how contact angle measurements on solid and liquid glue and on the substrate provide important information about the work of adhesion and interfacial tension determining short-term bonding and long-term adhesion, respectively.


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Tak-Sing Wong; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802

 

Self-Cleaning Characteristics of Slippery Liquid-Infused Porous Surfaces (SLIPS)

 

(Abstract not yet available)

 

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W. Xu, X. Li, Y. Tian, H. Bisaria, C.-H. Choi, and E.-H. Yang; Department of Mechanical Engineering, Stevens Institute of Technology, New Jersey, USA

 

E-mail: wxu1@stevens.edu

 

Transportation of a Microdroplet at Ultra-low Voltages by Tunable Wetting on Conjugated Polymer Electrodes

 

Transportation of microdroplets has broad applications in microfluidic system, lab-on-a-chip technology, biotechnology, and sensor devices. Although the actuation mechanisms of most devices so far are based on continuous flow through closed channels, strategies based on surface tension gradient have recently attracted much attention for the transportation of droplets. The surface tension gradient could be induced by an electrical, light, chemical, thermo, structural, or phase transformation gradient. Among those known techniques, electrowetting on dielectric (EWOD) technique is considered a practical method. However, EWOD-based techniques typically require actuation voltages from 12 to 80V, which could interfere with biological applications. Therefore, an alternative technique to realize low-voltage transportation of liquid droplets would be beneficial. Here, we demonstrate a controlled lateral transportation of an organic liquid droplet at ultra-low voltages (0.9 V) on dodecylbenzenesulfonate doped polypyrrole (PPy(DBS)) electrodes, by utilizing the tunable wetting property of PPy(DBS) surface in reduction and oxidation reactions. The PPy(DBS) electrode patterns are prepared by electrodeposition of PPy(DBS) film on micropatterned conductive electrodes. This result shows the potential of the tunable wetting of PPy(DBS) surface for ultra-low voltage microfluidics applications.

 

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Xianmin Xu; The State Key Lab. of Scientific & Engg. Computing, Chinese Academy of Sciences, Beijing 100080, P.R. CHINA

 

Mathematical Understandings of Contact Angle Hysteresis

 

(Abstract not yet available)

 

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