816,273 research outputs found
Order of wetting transitions in electrolyte solutions
For wetting films in dilute electrolyte solutions close to charged walls we
present analytic expressions for their effective interface potentials. The
analysis of these expressions renders the conditions under which corresponding
wetting transitions can be first- or second-order. Within mean field theory we
consider two models, one with short- and one with long-ranged solvent-solvent
and solvent-wall interactions. The analytic results reveal in a transparent way
that wetting transitions in electrolyte solutions, which occur far away from
their critical point (i.e., the bulk correlation length is less than half of
the Debye length) are always first-order if the solvent-solvent and
solvent-wall interactions are short-ranged. In contrast, wetting transitions
close to the bulk critical point of the solvent (i.e., the bulk correlation
length is larger than the Debye length) exhibit the same wetting behavior as
the pure, i.e., salt-free, solvent. If the salt-free solvent is governed by
long-ranged solvent-solvent as well as long-ranged solvent-wall interactions
and exhibits critical wetting, adding salt can cause the occurrence of an
ion-induced first-order thin-thick transition which precedes the subsequent
continuous wetting as for the salt-free solvent.Comment: Submitte
The local phase transitions of the solvent in the neighborhood of a solvophobic polymer at high pressures
We investigate local phase transitions of the solvent in the neighborhood of
a solvophobic polymer chain which is induced by a change of the polymer-solvent
repulsion and the solvent pressure in the bulk solution. We describe the
polymer in solution by the Edwards model, where the conditional partition
function of the polymer chain at a fixed radius of gyration is described by a
mean-field theory. The contributions of the polymer-solvent and the
solvent-solvent interactions to the total free energy are described within the
mean-field approximation. We obtain the total free energy of the solution as a
function of the radius of gyration and the average solvent number density
within the gyration volume. The resulting system of coupled equations is solved
varying the polymer-solvent repulsion strength at high solvent pressure in the
bulk. We show that the coil-globule (globule-coil) transition occurs
accompanied by a local solvent evaporation (condensation) within the gyration
volum
Diffusion of solvent from a cast cellulose acetate solution during the formation of skinned membranes
The transport of solvent out of a cast cellulose acetate (CA) solution into the coagulation bath during membrane formation is treated as a diffusion process. From the increase of solvent concentration in the bath with time (solvent leaching experiments) an overall solvent diffusion coefficient has been calculated. In size these coefficients compare well to mutual pseudo-binary solvent-non-solvent diffusion coefficients determined by means of a classical boundary broadening method applied to ternary solutions with fixed CA concentration, but with a gradient in solvent-nonsolvent composition. Since binary polymer-solvent interdiffusion coefficients are at least one order of magnitude lower, it is concluded that the diffusion of solvent into the coagulation bath is essentially a pseudo-binary solvent-non-solvent diffusion process. Combination of experimental results with model calculations for the effect of a thin dense skin on the diffusion of solvent out of the sublayer shows that the casting-leaching diffusion coefficient can be used to describe the out-diffusion of solvent from the layer under the skin provided that the relative skin resistance is not too high, or that the skin thickness is small
Process For Recovering Alcohol With Energy Integration
A process for recovering alcohol by a continuous process employing fermentation, solvent extraction of the alcohol product, extractive distillation of the alcohol-solvent extract to provide water fraction and vacuum stripping for separation of the alcohol and regenerated solvent.The solvent is recycled. An isoparaffin is used as a solvent and this solvent can be modified with a long chain fatty acid, alcohol or fatty alcohol or long-chain esters. Alternatively, many modifiers may be used neat.Georgia Tech Research Corporatio
The mechanism of formation of microporous or skinned membranes produced by immersion precipitation
Cellulose acetate and polysulfone casting solutions were coagulated in water/solvent mixtures with differing solvent content. Precipitation in pure water yielded skinned membranes. Precipitation in water/solvent mixtures with solvent concentration exceeding a certain minimum value (which is different for different systems) resulted in microporous membranes. This phenomenon has been explained in terms of the model description for the formation of asymmetric membranes as adopted in our laboratory. In this model, the skin formation is related to gelation and the formation of the porous substructure to liquid—liquid phase separation.\ud
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It is made plausible that the addition of solvent to the coagulation bath favours non-solvent inflow and hence liquid—liquid demixing in the precipitating film
Critical Casimir forces and colloidal aggregation: A numerical study
We present a numerical study of the effective potential
between two hard-sphere colloids dispersed in a solvent of interacting
particles, for several values of temperature and solvent density, approaching
the solvent gas-liquid critical point. We investigate the stability of a system
of particles interacting via to evaluate the locus of
colloidal aggregation in the solvent phase-diagram, and its dependence on the
colloid size. We assess how the excluded volume depletion forces are modified
by solvent attraction and discuss under which conditions solvent critical
fluctuations, in the form of critical Casimir forces, can be used to
effectively manipulate colloidal aggregation
The structure of fluids with impurities
The influence of dilute impurities on the structure of a fluid solvent is
investigated theoretically. General arguments, which do not rely on particular
models, are used to derive an extension of the Ornstein-Zernike form for the
solvent structure factor at small scattering vectors. It is shown that dilute
impurities can influence the solvent structure only if they are composed of
ions with significantly different sizes. Non-ionic impurities or ions of
similar size are shown to not alter the solvent structure qualitatively. This
picture is compatible with available experimental data. The derived form of the
solvent structure factor is expected to be useful to infer information on the
impurity-solvent interactions form measured scattering intensities
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