2,398 research outputs found
Effect of Salt Concentration on the Electrophoretic Speed of a Polyelectrolyte through a Nanopore
In a previous paper [S. Ghosal, Phys. Rev. E 74, 041901 (2006)] a
hydrodynamic model for determining the electrophoretic speed of a
polyelectrolyte through an axially symmetric slowly varying nanopore was
presented in the limit of a vanishingly small Debye length. Here the case of a
finite Debye layer thickness is considered while restricting the pore geometry
to that of a cylinder of length much larger than the diameter. Further, the
possibility of a uniform surface charge on the walls of the nanopore is taken
into account. It is thereby shown that the calculated transit times are
consistent with recent measurements in silicon nanopores.Comment: 4 pages, 2 figure
Systematic characterization of thermodynamic and dynamical phase behavior in systems with short-ranged attraction
In this paper we demonstrate the feasibility and utility of an augmented
version of the Gibbs ensemble Monte Carlo method for computing the phase
behavior of systems with strong, extremely short-ranged attractions. For
generic potential shapes, this approach allows for the investigation of
narrower attractive widths than those previously reported. Direct comparison to
previous self-consistent Ornstein-Zernike approximation calculations are made.
A preliminary investigation of out-of-equilibrium behavior is also performed.
Our results suggest that the recent observations of stable cluster phases in
systems without long-ranged repulsions are intimately related to gas-crystal
and metastable gas-liquid phase separation.Comment: 10 pages, 8 figure
Velocity fluctuations and hydrodynamic diffusion in sedimentation
We study non-equilibrium velocity fluctuations in a model for the
sedimentation of non-Brownian particles experiencing long-range hydrodynamic
interactions. The complex behavior of these fluctuations, the outcome of the
collective dynamics of the particles, exhibits many of the features observed in
sedimentation experiments. In addition, our model predicts a final relaxation
to an anisotropic (hydrodynamic) diffusive state that could be observed in
experiments performed over longer time ranges.Comment: 7 pages, 5 EPS figures, EPL styl
Effective non-additive pair potential for lock-and-key interacting particles: the role of the limited valence
Theoretical studies of self-assembly processes and condensed phases in
colloidal systems are often based on effective inter-particle potentials. Here
we show that developing an effective potential for particles interacting with a
limited number of ``lock-and-key'' selective bonds (due to the specificity of
bio-molecular interactions) requires -- beside the non-sphericity of the
potential -- a (many body) constraint that prevent multiple bonding on the same
site. We show the importance of retaining both valence and bond-selectivity by
developing, as a case study, a simple effective potential describing the
interaction between colloidal particles coated by four single-strand DNA
chains.Comment: 4 pages, 5 figure
Reverse-selective diffusion in nanocomposite membranes
The permeability of certain polymer membranes with impenetrable
nanoinclusions increases with the particle volume fraction (Merkel et al.,
Science, 296, 2002). This intriguing observation contradicts even qualitative
expectations based on Maxwell's classical theory of conduction/diffusion in
composites with homogeneous phases. This letter presents a simple theoretical
interpretation based on classical models of diffusion and polymer physics. An
essential feature of the theory is a polymer-segment depletion layer at the
inclusion-polymer interface. The accompanying increase in free volume leads to
a significant increase in the local penetrant diffusivity, which, in turn,
increases the bulk permeability while exhibiting reverse selectivity. This
model captures the observed dependence of the bulk permeability on the
inclusion size and volume fraction, providing a straightforward connection
between membrane microstructure and performance
Critical behaviors of sheared frictionless granular materials near jamming transition
Critical behaviors of sheared dense and frictionless granular materials in
the vicinity of the jamming transition are numerically investigated. From the
extensive molecular dynamics simulation, we verify the validity of the scaling
theory near the jamming transition proposed by Otsuki and Hayakawa (Prog.
Theor. Phys., 121, 647 (2009)). We also clarify the critical behaviors of the
shear viscosity and the pair correlation function based on both a phenomenology
and the simulation.Comment: 13pages, 26 figure
Micro-evaporators for kinetic exploration of phase diagrams
We use pervaporation-based microfluidic devices to concentrate species in
aqueous solutions with spatial and temporal control of the process. Using
experiments and modelling, we quantitatively describe the advection-diffusion
behavior of the concentration field of various solutions (electrolytes,
colloids, etc) and demonstrate the potential of these devices as universal
tools for the kinetic exploration of the phases and textures that form upon
concentration
Influence of shear stress applied during flow stoppage and rest period on the mechanical properties of thixotropic suspensions
We study the solid mechanical properties of several thixotropic suspensions
as a function of the shear stress history applied during their flow stoppage
and their aging in their solid state. We show that their elastic modulus and
yield stress depend strongly on the shear stress applied during their
solid-liquid transition (i.e., during flow stoppage) while applying the same
stress only before or only after this transition may induce only second-order
effects: there is negligible dependence of the mechanical properties on the
preshear history and on the shear stress applied at rest. We also found that
the suspensions age with a structuration rate that hardly depends on the stress
history. We propose a physical sketch based on the freezing of a microstructure
whose anisotropy depends on the stress applied during the liquid-solid
transition to explain why the mechanical properties depend strongly on this
stress. This sketch points out the role of the internal forces in the colloidal
suspensions' behavior. We finally discuss briefly the macroscopic consequences
of this phenomenon and show the importance of using a controlled-stress
rheometer
Dynamic regimes of hydrodynamically coupled self-propelling particles
We analyze the collective dynamics of self-propelling particles (spps) which
move at small Reynolds numbers including the hydrodynamic coupling to the
suspending solvent through numerical simulations. The velocity distribution
functions show marked deviations from Gaussian behavior at short times, and the
mean-square displacement at long times shows a transition from diffusive to
ballistic motion for appropriate driving mechanism at low concentrations. We
discuss the structures the spps form at long times and how they correlate to
their dynamic behavior.Comment: 7 pages, 4 figure
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