35 research outputs found
Surface-Directed Spinodal Decomposition: A Molecular Dynamics Study
We use molecular dynamics (MD) simulations to study surface-directed spinodal
decomposition (SDSD) in unstable binary () fluid mixtures at wetting
surfaces. The thickness of the wetting layer grows with time as a
power-law (). We find that hydrodynamic effects result in a
crossover of the growth exponent from to . We
also present results for the layer-wise correlation functions and domain length
scales.Comment: 29 pages, 13 figures, submitted to PR
Morphological Phase Separation in Unstable Thin Films: Pattern Formation and Growth
We present results from a comprehensive numerical study of {\it morphological
phase separation} (MPS) in unstable thin liquid films on a 2-dimensional
substrate. We study the quantitative properties of the evolution morphology via
several experimentally relevant markers, e.g., correlation function, structure
factor, domain-size and defect-size probability distributions, and growth laws.
Our results suggest that the late-stage morphologies exhibit dynamical scaling,
and their evolution is self-similar in time. We emphasize the analogies and
differences between MPS in films and segregation kinetics in unstable binary
mixtures.Comment: 17 pages, 6 figures; Accepted for publication in Physical Chemistry
Chemical Physic
Spinodal Phase Separation in Liquid Films with Quenched Disorder
We study spinodal phase separation in unstable thin liquid films on
chemically disordered substrates via simulations of the thin-film equation. The
disorder is characterized by immobile patches of varying size and Hamaker
constant. The effect of disorder is pronounced in the early stages
(amplification of fluctuations), remains during the intermediate stages and
vanishes in the late stages (domain growth). These findings are in contrast to
the well-known effects of quenched disorder in usual phase-separation
processes, viz., the early stages remain undisturbed and domain growth is
slowed down in the asymptotic regime. We also address the inverse problem of
estimating disorder by thin-film experiments.Comment: 12 pages, 7 figure
Shear Transformation Zones: State Determined or Protocol Dependent?
The concept of a Shear Transformation Zone (STZ) refers to a region in an
amorphous solid that undergoes a plastic event when the material is put under
an external mechanical load. An important question that had accompanied the
development of the theory of plasticity in amorphous solids for many years now
is whether an STZ is a {\em region} existing in the material (which can be
predicted by analyzing the unloaded material), or is it an {\em event} that
depends on the loading protocol (i.e., the event cannot be predicted without
following the protocol itself). In this Letter we present strong evidence that
the latter is the case. Infinitesimal changes of protocol result in
macroscopically big jumps in the positions of plastic events, meaning that
these can never be predicted from considering the unloaded material.Comment: 4 pages, 5 figure
Kinetics of Spinodal Phase Separation in Unstable Thin Liquid Films
We study universality in the kinetics of spinodal phase separation in
unstable thin liquid films, via simulations of the thin film equation. It is
shown that in addition to morphology and free energy,the number density of
local maxima in the film profile can also be used to identify the early,
intermediate and late stages of spinodal phase separation. A universal curve
between the number density of local maxima and rescaled time describes the
kinetics of early stage in d = 2, 3. The Lifshitz-Slyozov exponent of -1/3
describes the kinetics of the late stage in d = 2 even in the absence of
coexisting equilibrium phases.Comment: 5 figure
Modeling Barkhausen Noise in Magnetic Glasses with Dipole-Dipole Interactions
Long-ranged dipole-dipole interactions in magnetic glasses give rise to
magnetic domains having labyrinthine patterns. Barkhausen Noise is then
expected to result from the movement of domain boundaries which is supposed to
be modeled by the motion of elastic membranes with random pinning. We propose
an atomistic model of such magnetic glasses in which we measure the Barkhausen
Noise which indeed results from the movement of domain boundaries. Nevertheless
the statistics of the Barkhausen Noise is found in striking disagreement with
the expectations in the literature. In fact we find exponential statistics
without any power law, stressing the fact that Barkhausen Noise can belong to
very different universality classes. In this glassy system the essence of the
phenomenon is the ability of spin-carrying particles to move and minimize the
energy without any spin flip. A theory is offered in excellent agreement with
the measured data without any free parameter.Comment: 5 Pages, 5 Figures, Submitted to EP
Kinetics of Surface Enrichment: A Molecular Dynamics Study
We use molecular dynamics (MD) to study the kinetics of surface enrichment
(SE) in a stable homogeneous mixture (AB), placed in contact with a surface
which preferentially attracts A. The SE profiles show a characteristic
double-exponential behavior with two length scales: \xi_-, which rapidly
saturates to its equilibrium value, and \xi_+, which diverges as a power-law
with time (\xi_+ \sim t^\theta). We find that hydrodynamic effects result in a
crossover of the growth exponent from \theta \simeq 0.5 to \theta \simeq 1.0.
There is also a corresponding crossover in the growth dynamics of the SE-layer
thickness.Comment: 20 pages, 6 figures, Published in J. Chem. Phys. (Research
Highlights