94 research outputs found
Universality for 2D Wedge Wetting
We study 2D wedge wetting using a continuum interfacial Hamiltonian model
which is solved by transfer-matrix methods. For arbitrary binding potentials,
we are able to exactly calculate the wedge free-energy and interface height
distribution function and, thus, can completely classify all types of critical
behaviour. We show that critical filling is characterized by strongly universal
fluctuation dominated critical exponents, whilst complete filling is determined
by the geometry rather than fluctuation effects. Related phenomena for
interface depinning from defect lines in the bulk are also considered.Comment: 4 pages, 1 figur
Geometry dominated fluid adsorption on sculptured substrates
Experimental methods allow the shape and chemical composition of solid
surfaces to be controlled at a mesoscopic level. Exposing such structured
substrates to a gas close to coexistence with its liquid can produce quite
distinct adsorption characteristics compared to that occuring for planar
systems, which may well play an important role in developing technologies such
as super-repellent surfaces or micro-fluidics. Recent studies have concentrated
on adsorption of liquids at rough and heterogeneous substrates and the
characterisation of nanoscopic liquid films. However, the fundamental effect of
geometry has hardly been addressed. Here we show that varying the shape of the
substrate can exert a profound influence on the adsorption isotherms allowing
us to smoothly connect wetting and capillary condensation through a number of
novel and distinct examples of fluid interfacial phenomena. This opens the
possibility of tailoring the adsorption properties of solid substrates by
sculpturing their surface shape.Comment: 6 pages, 4 figure
Superhydrophobic Surface Based on a Coral-Like Hierarchical Structure of ZnO
Background: Fabrication of superhydrophobic surfaces has attracted much interest in the past decade. The fabrication methods that have been studied are chemical vapour deposition, the sol-gel method, etching technique, electrochemical deposition, the layer-by-layer deposition, and so on. Simple and inexpensive methods for manufacturing environmentally stable superhydrophobic surfaces have also been proposed lately. However, work referring to the influence of special structures on the wettability, such as hierarchical ZnO nanostructures, is rare. Methodology: This study presents a simple and reproducible method to fabricate a superhydrophobic surface with microscale roughness based on zinc oxide (ZnO) hierarchical structure, which is grown by the hydrothermal method with an alkaline aqueous solution. Coral-like structures of ZnO were fabricated on a glass substrate with a micro-scale roughness, while the antennas of the coral formed the nano-scale roughness. The fresh ZnO films exhibited excellent superhydrophilicity (the apparent contact angle for water droplet was about 0u), while the ability to be wet could be changed to superhydrophobicity after spin-coating Teflon (the apparent contact angle greater than 168u). The procedure reported here can be applied to substrates consisting of other materials and having various shapes. Results: The new process is convenient and environmentally friendly compared to conventional methods. Furthermore, the hierarchical structure generates the extraordinary solid/gas/liquid three-phase contact interface, which is the essentia
Wettability Switching Techniques on Superhydrophobic Surfaces
The wetting properties of superhydrophobic surfaces have generated worldwide research interest. A water drop on these surfaces forms a nearly perfect spherical pearl. Superhydrophobic materials hold considerable promise for potential applications ranging from self cleaning surfaces, completely water impermeable textiles to low cost energy displacement of liquids in lab-on-chip devices. However, the dynamic modification of the liquid droplets behavior and in particular of their wetting properties on these surfaces is still a challenging issue. In this review, after a brief overview on superhydrophobic states definition, the techniques leading to the modification of wettability behavior on superhydrophobic surfaces under specific conditions: optical, magnetic, mechanical, chemical, thermal are discussed. Finally, a focus on electrowetting is made from historical phenomenon pointed out some decades ago on classical planar hydrophobic surfaces to recent breakthrough obtained on superhydrophobic surfaces
Nemateriālo aktīvu grāmatvedības metodoloģiskās problēmas Latvijas Republikā
Nonfluorinated hydrophobic surfaces
are of interest for reduced
cost, toxicity, and environmental problems. Searching for such surfaces
together with versatile processing, A200 silica nanoparticles are
modified with an oligodimethylsiloxane and used by themselves or with
a polymer matrix. The goal of the surface modification is controlled
aggregate size and stable suspensions. Characterization is done by
NMR, microanalysis, nitrogen adsorption, and dynamic light scattering.
The feasibility of the concept is then demonstrated. The silica aggregates
are sprayed in a scalable process to form ultrahydrophobic and imperceptible
coatings with surface topographies of controlled nanoscale roughness
onto different supports, including nanofibrillated cellulose. To improve
adhesion and wear properties, the organosilica was mixed with polymers.
The resulting composite coatings are characterized by FE-SEM, AFM,
and contact angle measurements. Depending on the nature of the polymer,
different functionalities can be developed. Poly(methyl methacrylate)
leads to almost superhydrophobic and highly transparent coatings.
Composites based on commercial acrylic car paint show “pearl-bouncing”
droplet behavior. A light-emitting polyfluorene is synthesized to
prepare luminescent and water repellent coatings on different supports.
The interactions between polymers and the organosilica influence coating
roughness and are critical for wetting behavior. In summary, the feasibility
of a facile, rapid, and fluorine-free hydrophobization concept was
successfully demonstrated in multipurpose antiwetting applications
Fabrication and characterization of transparent superhydrophobic thin films based on silica nanoparticles
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