90 research outputs found
Casimir forces in modulated systems
For the first time we present analytical results for the contribution of
electromagnetic fluctuations into thermodynamic properties of modulated
systems, like cholesteric or smectic liquid crystalline films. In the case of
small dielectric anisotropy we have derived explicit analytical expressions for
the chemical potential of such systems. Two limiting cases were specifically
considered: (i) the Van der Waals (VdW) limit, i.e., in the case when the
retardation of the electromagnetic interactions can be neglected; and (ii) the
Casimir limit, i.e. when the effects of retardation becomes considerable. It
was shown that in the Casimir limit, the film chemical potential oscillates
with the thickness of the film. This non-monotonic dependence of the chemical
potential on the film thickness can lead to step-wise wetting phenomena,
surface anchoring reorientation and other important effects. Applications of
the results may concern the various systems in soft matter or condensed matter
physics with multilayer or modulated structures.Comment: 13 page
Scaling and Crossover to Tricriticality in Polymer Solutions
We propose a scaling description of phase separation of polymer solutions.
The scaling incorporates three universal limiting regimes: the Ising limit
asymptotically close to the critical point of phase separation, the "ideal-gas"
limit for the pure-solvent phase, and the tricritical limit for the
polymer-rich phase asymptotically close to the theta point. We have also
developed a phenomenological crossover theory based on the
near-tricritical-point Landau expansion renormalized by fluctuations. This
theory validates the proposed scaled representation of experimental data and
crossover to tricriticality.Comment: 4 pages, 3 figure
Dislocation loops in overheated free-standing smectic films
Static and dynamic phenomena in overheated free-standing smectic-A films are
studied using a generalization of de Gennes' theory for a confined presmectic
liquid. A static application is to determine the profile of the film meniscus
and the meniscus contact angle, the results being compared with those of a
recent study employing de Gennes' original theory. The dynamical generalization
of the theory is based on on a time-dependent Ginzburg-Landau approach. This is
used to compare two modes for layer-thinning transitions in overheated films,
namely "uniform thinning" vs. nucleation of dislocation loops. Properties such
as the line tension and velocity of a moving dislocation line are evaluated
self-consistently by the theory.Comment: 16 pages, 8 figure
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