13,286 research outputs found
Contact angles on heterogeneous surfaces; a new look at Cassie's and Wenzel's laws
We consider a three dimensional liquid drop sitting on a rough and chemically
heterogeneous substrate. Using a novel minimization technique on the free
energy of this system, a generalized Young's equation for the contact angle is
found. In certain limits, the Cassie and Wenzel laws, and a new equivalent
rule, applicable in general, are derived. We also propose an equation in the
same spirit as these results but valid on a more `microscopic' level.
Throughout we work under the presence of gravity and keep account of line
tension terms.Comment: 10 pages RevTeX, 2 EPS figures. A few minor corrections mad
Wetting between structured surfaces: Liquid bridges and induced forces
Wetting phenomena are theoretically studied for a slab geometry
consisting of a wetting phase confined between two chemically
patterned substrates. Each of these is decorated by an array of
stripes whose composition alternates between two different surface
phases. For a single pair of opposing stripes, the wetting phase may
either form a bridge spanning from one surface to the other or it may
break up into two separate channels. The bridge state induces an
effective interaction between the two substrates. This leads to the
bridge itself having a preferred contact angle and the substrates
having a preferred separation. In the case of many stripes, one has a
whole sequence of morphological transitions with the number of bridges
decreasing as the surface separation grows
The Influence of Substrate Structure on Membrane Adhesion
We consider a membrane both weakly and strongly adhering to a geometrically
structured substrate. The interaction potential is assumed to be local, via the
Deryagin approximation, and harmonic. Consequently, we can analytically
describe a variety of different geometries: as well as randomly rough
self-affine surfaces, smooth substrates interrupted by an isolated cylindrical
pit, a single elongated trench or a periodic array of trenches are
investigated. We present more general expressions for the adhesion energy and
membrane configuration in Fourier space and find that, compared to planar
surfaces, the adhesion energy decreases. We also highlight the possibility of
overshoots occurring in the membrane profile and look at its degree of
penetration into surface indentations.Comment: 41 pages LaTex, 12 EPS figure
An exact solution for two dimensional wetting with a corrugated wall
An exact solution of a two dimensional RSOS model of wetting at a corrugated
(periodic) wall is found using transfer matrix techniques. In contrast to
mean-field analysis of the same problem the wetting transition remains
second-order and occurs at a lower temperature than that of the planar system.
Comparison with numerical studies and other analytical approaches is made.Comment: 11 pages LaTex with 1 eps figure. To appear in J.Phys.
Corrugation-Induced First-Order Wetting: An Effective Hamiltonian Study
We consider an effective Hamiltonian description of critical wetting
transitions in systems with short-range forces at a corrugated (periodic) wall.
We are able to recover the results obtained previously from a `microscopic'
density-functional approach in which the system wets in a discontinuous manner
when the amplitude of the corrugations reaches a critical size A*. Using the
functional renormalization group, we find that A* becomes dependent on the
wetting parameter \omega in such a way as to decrease the extent of the
first-order regime. Nevertheless, we still expect wetting in the Ising model to
proceed in a discontinuous manner for small deviations of the wall from the
plane.Comment: 9 pages RevTex with 2 EPS figures. To appear in Eur. Phys. J.
Coupled Hamiltonians and Three Dimensional Short-Range Wetting Transitions
We address three problems faced by effective interfacial Hamiltonian models
of wetting based on a single collective coordinate \ell representing the
position of the unbinding fluid interface. Problems (P1) and (P2) refer to the
predictions of non-universality at the upper critical dimension d=3 at critical
and complete wetting respectively which are not borne out by Ising model
simulation studies. (P3) relates to mean-field correlation function structure
in the underlying continuum Landau model. We investigate the hypothesis that
these concerns arise due to the coupling of order parameter fluctuations near
the unbinding interface and wall. For quite general choices of collective
coordinates X_i we show that arbitrary two-field models H[X_1,X_2] can recover
the required anomalous structure of mean-field correlation functions (P3). To
go beyond mean-field theory we introduce a set of Hamiltonians based on proper
collective coordinates s near the wall which have both interfacial and
spin-like components. We argue that an optimum model H[s,\ell] in which the
degree of coupling is controlled by an angle-like variable, best describes the
non-universality of the Ising model and investigate its critical behaviour. For
critical wetting the appropriate Ginzburg criterion shows that the true
asymptotic critical regime for the local susceptibility \chi_1 is dramatically
reduced consistent with observations of mean-field behaviour in simulations
(P1). For complete wetting the model yields a precise expression for the
temperature dependence of the renormalized critical amplitude \theta in good
agreement with simulations (P2). We highlight the importance of a new wetting
parameter which describes the physics that emerges due to the coupling effects.Comment: 34 pages, RevTex, 8 eps figures. To appear in Physica
Contextual classification of multispectral image data
There are no author-identified significant results in this report
Aerosil in Solid-state Buccal Film for Improved and Sustained Delivery of Valsartan: Molecular Docking Studies
To overcome low oral bioavailability and short biological half-life, improved and sustained buccal delivery of valsartan has been proposed. Valsartan film with colloidal silicon dioxide has been prepared using HPMC as mucoadhesive polymer matrix by casting and solvent evaporation method. Valsartan and Aerosil might have been interacted by hydrogen bond formation between adsorbed water and silanol of SiO2. In vitro drug release and ex vivo buccal permeation increased with the increase of Aerosil in the film. The formulation of valsartan to Aerosil at 1:0.02 ratio exhibited a sustained type of release and permeation of 80 and 70 %, respectively, in 8 h of study in simulated physiological fluid (pH 6.8). Molecular docking study revealed a stable configuration with favourable score of â2.15 kcal molâ1 of the Aerosil incorporated valsartan buccal film. In conclusion, Aerosil incorporated hydrogel forming buccal film could be used for improved and sustained delivery of valsartan.
This work is licensed under a Creative Commons Attribution 4.0 International License
Two Parameters for Three Dimensional Wetting Transitions
Critical effects at complete and critical wetting in three dimensions are
studied using a coupled effective Hamiltonian H[s(y),\ell]. The model is
constructed via a novel variational principle which ensures that the choice of
collective coordinate s(y) near the wall is optimal. We highlight the
importance of a new wetting parameter \Omega(T) which has a strong influence on
critical properties and allows the status of long-standing Monte-Carlo
simulation controversies to be re-examined.Comment: 4 pages RevTex, 2 encapsulated postscript figures, to appear in
Europhys. Let
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