18,144 research outputs found
Relation between the thermodynamic Casimir effect in Bose-gas slabs and critical Casimir forces
In a recent letter, Martin and Zagrebnov [Europhys. Lett., 73 (2006) 1]
discussed the thermodynamic Casimir effect for the ideal Bose gas confined in a
thin film. We point out that their findings can be expressed in terms of
previous general results for the Casimir effect induced by confined critical
fluctuations. This highlights the links between the Casimir effect in the
contexts of critical phenomena and Bose-Einstein condensation.Comment: Comment on cond-mat/050726
Wetting and capillary nematization of binary hard-platelet and hard-rod fluids
Density-functional theory is used to investigate the phase behavior of
colloidal binary hard-platelet and hard-rod fluids near a single hard wall or
confined in a slit pore. The Zwanzig model, in which the orientations of the
particles of rectangular shape are restricted to three orthogonal orientations,
is analyzed by numerical minimization of the grand potential functional. The
density and orientational profiles as well as the surface contributions to the
grand potential are determined. The calculations exhibit a wall-induced
continuous surface transition from uniaxial to biaxial symmetry for the
hard-rod fluid. Complete wetting of the wall -- isotropic liquid interface by a
biaxial nematic film for rods and a uniaxial nematic film for platelets is
found. For the fluids confined by two parallel hard walls we determine a
first-order capillary nematization transition for large slit widths, which
terminates in a capillary critical point upon decreasing the slit width.Comment: 11 pages, 11 figure
Structure factor of thin films near continuous phase transitions
The two-point correlation function in thin films is studied near the critical
point of the corresponding bulk system. Based on fieldtheoretic renormalization
group theory the dependences of this correlation function on the lateral
momentum, the two distances normal to the free surfaces, temperature, and film
thickness are determined. The corresponding scattering cross section of X-rays
and neutrons under grazing incidence is calculated. It reveals the various
singularities of the two-point correlation function.Comment: 61 pages, 14 figures, submitted to PR
Magnetization of multicomponent ferrofluids
The solution of the mean spherical approximation (MSA) integral equation for
isotropic multicomponent dipolar hard sphere fluids without external fields is
used to construct a density functional theory (DFT), which includes external
fields, in order to obtain an analytical expression for the external field
dependence of the magnetization of ferrofluidic mixtures. This DFT is based on
a second-order Taylor series expansion of the free energy density functional of
the anisotropic system around the corresponding isotropic MSA reference system.
The ensuing results for the magnetic properties are in quantitative agreement
with our canonical ensemble Monte Carlo simulation data presented here.Comment: 12 pages including 4 figure
Diffusive spreading and mixing of fluid monolayers
The use of ultra-thin, i.e., monolayer films plays an important role for the
emerging field of nano-fluidics. Since the dynamics of such films is governed
by the interplay between substrate-fluid and fluid-fluid interactions, the
transport of matter in nanoscale devices may be eventually efficiently
controlled by substrate engineering. For such films, the dynamics is expected
to be captured by two-dimensional lattice-gas models with interacting
particles. Using a lattice gas model and the non-linear diffusion equation
derived from the microscopic dynamics in the continuum limit, we study two
problems of relevance in the context of nano-fluidics. The first one is the
case in which along the spreading direction of a monolayer a mesoscopic-sized
obstacle is present, with a particular focus on the relaxation of the fluid
density profile upon encountering and passing the obstacle. The second one is
the mixing of two monolayers of different particle species which spread side by
side following the merger of two chemical lanes, here defined as domains of
high affinity for fluid adsorption surrounded by domains of low affinity for
fluid adsorption.Comment: 12 pages, 3 figure
Stability of liquid ridges on chemical micro- and nanostripes
We analyze the stability of sessile filaments (ridges) of nonvolatile liquids
versus pearling in the case of externally driven flow along a chemical stripe
within the framework of the thin film approximation. The ridges can be stable
with respect to pearling even if the contact line is not completely pinned. A
generalized stability criterion for moving contact lines is provided. For large
wavelengths and no drive, within perturbation theory, an analytical expression
of the growth rate of pearling instabilities is derived. A numerical analysis
shows that drive further stabilizes the ridge by reducing the growth rate of
unstable perturbations, even though there is no complete stabilization. Hence
the stability criteria established without drive ensure overall stability.Comment: 10 pages, 6 figure
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