1,591 research outputs found
Heterogeneous aggregation in binary colloidal alloys
Molecular dynamics (MD) simulation has been employed to study the
nonequilibrium structure formation of two types of particles in a colloidal
suspension, driven by type-dependent forces. We examined the time evolution of
structure formation as well as the structural properties of the resulting
aggregation by studying the radial distribution function (RDF). The resulting
aggregation is well described by a binary colloidal gelation. We compared the
structural properties to those for one type of particles. From the MD results,
it is evident that there are significant differences between the RDF's of the
two cases. Moreover, we found that the average coordination number is generally
larger in the monodisperse case for all area fractions considered. Thus, by
means of heterogeneous aggregation, it is possible to obtain a wide variety of
structures while more close-packed structures are formed for monodisperse
colloidal aggregation.Comment: 15 pages, 5 eps figures; preliminary results have been reported at
the APS March Meeting 2002; accepted by Physica
Nonlinear ER effects in an ac applied field
The electric field used in most electrorheological (ER) experiments is
usually quite high, and nonlinear ER effects have been theoretically predicted
and experimentally measured recently. A direct method of measuring the
nonlinear ER effects is to examine the frequency dependence of the same
effects. For a sinusoidal applied field, we calculate the ac response which
generally includes higher harmonics. In is work, we develop a multiple image
formula, and calculate the total dipole moments of a pair of dielectric
spheres, embedded in a nonlinear host. The higher harmonics due to the
nonlinearity are calculated systematically.Comment: Presented at Conference on Computational Physics (CCP2000), held at
Gold Coast, Australia from 3-8, December 200
Mean Field Theory for Lossy Nonlinear Composites
The mean-field theory for lossy nonlinear composites, described by complex
and field-dependent dielectric functions, is presented. By using the spectral
representation of linear composites with identical microstructure, we develop
self-consistent equations for the effective response. We examine two types of
microstructure, namely, the Maxwell-Garnett approximation and the effective
medium approximation to illustrate the theory.Comment: 11 pages, LaTeX format, 2 figures, accepted for publication by Solid
State Communications 18 November 199
Local field distribution near corrugated interfaces: Green's function formulation
We have developed a Green's function formalism to compute the local field
distribution near an interface separating two media of different dielectric
constants. The Maxwell's equations are converted into a surface integral
equation; thus it greatly simplifies the solutions and yields accurate results
for interfaces of arbitrary shape. The integral equation is solved and the
local field distribution is obtained for a periodic interface.Comment: Presented at the Conference on Computational Physics (CCP2000), held
at Gold Coast, Australia from 3 - 8, December 2000. To be published in
Proceedings of CCP200
Enhancement of Optical Nonlinearity Through Anisotropic Microstructures
We investigate the polarization dependence of optical nonlinearity
enhancement for a uniaxial anisotropic composite of metal nanocrystals in a
dielectric host. Three cases are distinguished depending on whether the
polarization is parallel, perpendicular or unpolarized with respect to the axis
of anisotropy. For the parallel polarization, the results show that the 3D
results are qualitatively similar to the 2D case reported recently. For the
perpendicular polarization, the results are markedly different from the
parallel counterpart: In contrast to the absorption, the enhancement factor
actually increases with the anisotropy. Thus the separation of the absorption
and enhancement peaks becomes even more pronounced than the parallel
polarization case. These results indicate a strong polarization dependence of
the nonlinear optical response.Comment: 12 pages, LaTeX format, 9 figures, preliminary results were Reported
in the 2nd Tohwa University International Meeting on Statistical Physics held
on November 4-7, 1997, accepted for publication by Optics Communications on 7
November 199
Spin scattering of a particle for periodic boundary conditions
We have studied anomalous diffusion of a particle in a random medium in which
the passage of the particle may modify the state of the visited sites. The
simplicity of the dynamics allows analytic solution. Interesting propagation
and organization behaviors will be reported.Comment: pdf fil
Effective nonlinear optical properties of composite media of graded spherical particles
We have developed a nonlinear differential effective dipole approximation
(NDEDA), in an attempt to investigate the effective linear and third-order
nonlinear susceptibility of composite media in which graded spherical
inclusions with weak nonlinearity are randomly embedded in a linear host
medium. Alternatively, based on a first-principles approach, we derived exactly
the linear local field inside the graded particles having power-law dielectric
gradation profiles. As a result, we obtain also the effective linear dielectric
constant and third-order nonlinear susceptibility. Excellent agreement between
the two methods is numerically demonstrated. As an application, we apply the
NDEDA to investigate the surface plasma resonant effect on the optical
absorption, optical nonlinearity enhancement, and figure of merit of
metal-dielectric composites. It is found that the presence of gradation in
metal particles yields a broad resonant band in the optical region, and further
enhances the figure of merit.Comment: 20 pages, 5 figure
Electrorotation of colloidal suspensions
When a strong electric field is applied to a colloidal suspension, it may
cause an aggregation of the suspended particles in response to the field. In
the case of a rotating field, the electrorotation (ER) spectrum can be modified
further due to the local field effects arising from the many-particle system.
To capture the local field effect, we invoke the Maxwell-Garnett approximation
for the dielectric response. The hydrodynamic interactions between the
suspended particles can also modify the spin friction, which is a key to
determine the angular velocity of ER. By invoking the spectral representation
approach, we derive the analytic expressions for the characteristic frequency
at which the maximum angular velocity of ER occurs. From the numerical
caculation, we find that there exist two sub-dispersions in the ER spectrum.
However, the two characteristic frequencies are so close that the two peaks
actually overlap and become a single broad peak. We report a detailed
investigation of the dependence of the characteristic frequency and the
dispersion strength of ER on various material parameters.Comment: RevTeX, 4 eps figures; clarifying discussion added in accord with
referees' reports; accepted by Physics Letters
Effective conductivity of composites of graded spherical particles
We have employed the first-principles approach to compute the effective
response of composites of graded spherical particles of arbitrary conductivity
profiles. We solve the boundary-value problem for the polarizability of the
graded particles and obtain the dipole moment as well as the multipole moments.
We provide a rigorous proof of an {\em ad hoc} approximate method based on the
differential effective multipole moment approximation (DEMMA) in which the
differential effective dipole approximation (DEDA) is a special case. The
method will be applied to an exactly solvable graded profile. We show that DEDA
and DEMMA are indeed exact for graded spherical particles.Comment: submitted for publication
Single-Particle Diffusion-Coefficient on Surfaces with Ehrlich-Schwoebel-Barriers
The diffusion coefficient of single particles in the presence of
Ehrlich-Schwoebel barriers (ESB)is considered. An exact expression is given for
the diffusion coefficient on linear chains with random arrangements of ESB. The
results are extended to surfaces having ESB with uniform extension in one or
both directions. All results are verified by Monte Carlo simulations.Comment: 11 pages, LaTeX2e, 6 eps-figure
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