379 research outputs found
Surface tension of isotropic-nematic interfaces: Fundamental Measure Theory for hard spherocylinders
A fluid constituted of hard spherocylinders is studied using a density
functional theory for non-spherical hard particles, which can be written as a
function of weighted densities. This is based on an extended deconvolution of
the Mayer -function for arbitrarily shaped convex hard bodies in tensorial
weight functions, which depend each only on the shape and orientation of a
single particle. In the course of an examination of the isotropic- nematic
interface at coexistence the functional is applied to anisotropic and
inhomogeneous problems for the first time. We find good qualitative agreement
with other theoretical predictions and also with Monte-Carlo simulations
Active Brownian particles at interfaces: An effective equilibrium approach
A simple theoretical approach is used to investigate active colloids at the free interface and near repulsive substrates. We employ dynamical density functional theory to determine the steady-state density profiles in an effective equilibrium system (Farage T. F. F. et al., Phys. Rev. E, 91 (2015) 042310). In addition to the known accumulation at surfaces, we predict wetting and drying transitions at a flat repulsive wall and capillary condensation and evaporation in a slit pore. These new phenomena are closely related to the motility-induced phase separation (MIPS) in the bulk
Fundamental measure theory for non-spherical hard particles: predicting liquid crystal properties from the particle shape
Density functional theory (DFT) for hard bodies provides a theoretical description of the effect of particle shape on inhomogeneous fluids. We present improvements of the DFT framework fundamental measure theory (FMT) for hard bodies and validate these improvements for hard spherocylinders. To keep the paper self-contained, we first discuss the recent advances in FMT for hard bodies that lead to the introduction of fundamental mixed measure theory (FMMT) in our previous paper (2015 Europhys. Lett. 109 26003). Subsequently, we provide an efficient semi-empirical alternative to FMMT and show that the phase diagram for spherocylinders is described with similar accuracy in both versions of the theory. Finally, we present a semi-empirical modification of FMMT whose predictions for the phase diagram for spherocylinders are in excellent quantitative agreement with computer simulation results
Escape rate of active particles in the effective equilibrium approach
The escape rate of a Brownian particle over a potential barrier is accurately described by the Kramers theory. A quantitative theory explicitly taking the activity of Brownian particles into account has been lacking due to the inherently out-of-equilibrium nature of these particles. Using an effective equilibrium approach [Farage et al., Phys. Rev. E 91, 042310 (2015)] we study the escape rate of active particles over a potential barrier and compare our analytical results with data from direct numerical simulation of the colored noise Langevin equation. The effective equilibrium approach generates an effective potential that, when used as input to Kramers rate theory, provides results in excellent agreement with the simulation data
Particle-conserving dynamics on the single-particle level
We generalize the particle-conserving dynamics method of de las Heras et al. [J. Phys.: Condens. Matter 28, 244024 (2016)] to binary mixtures and apply this to hard rods in one dimension. Considering the case of one species consisting of only one particle enables us to address the tagged-particle dynamics. The time-evolution of the species-labeled density profiles is compared to exact Brownian dynamics and (grand- canonical) dynamical density functional theory. The particle-conserving dynamics yields improved results over the dynamical density functional theory and well reproduces the simulation data at short and intermediate times. However, the neglect of a strict particle order (due to the fundamental statistical assumption of ergodicity) leads to errors at long times for our one-dimensional setup. The isolated study of that error makes clear the fundamental limitations of (adiabatic) density-based theoretical approaches when applied to systems of any dimension for which particle caging is a dominant physical mechanism
Density functional approach to elastic properties of three-dimensional dipole-spring models for magnetic gels
Magnetic gels are composite materials, consisting of a polymer matrix and
embedded magnetic particles. Those are mechanically coupled to each other,
giving rise to the magnetostrictive effects as well as to a controllable
overall elasticity responsive to external magnetic fields. Due to their
inherent composite and thereby multiscale nature, a theoretical framework
bridging different levels of description is indispensable for understanding the
magnetomechanical properties of magnetic gels. In this study, we extend a
recently developed density functional approach from two spatial dimensions to
more realistic three-dimensional systems. Along these lines, we connect a
mesoscopic characterization resolving the discrete structure of the magnetic
particles, to macroscopic continuum parameters of magnetic gels. In particular,
we incorporate the long-range nature of the magnetic dipole-dipole interaction,
and consider the approximate incompressibility of the embedding media, and
relative rotations with respect to an external magnetic field breaking
rotational symmetry. We then probe the shape of the model system in its
reference state, confirming the dependence of magnetostrictive effects on the
configuration of the magnetic particles and on the shape of the considered
sample. Moreover, calculating the elastic and rotational coefficients on the
basis of our mesoscopic approach, we examine how the macroscopic types of
behavior are related to the mesoscopic properties. Implications for real
systems of random particle configurations are also discussed.Comment: 16 pages, 4 figure
Biaxial nematic order in fundamental measure theory
Liquid crystals consisting of biaxial particles can exhibit a much richer
phase behavior than their uniaxial counterparts. Usually, one has to rely on
simulation results to understand the phase diagram of these systems, since very
few analytical results exist. In this work, we apply fundamental measure
theory, which allows to derive free energy functionals for hard particles from
first principles and with quantitative accuracy, to systems of hard cylinders,
cones and spherotriangles. We provide a general recipe for incorporating
biaxial liquid crystal order parameters into fundamental measure theory and use
this framework to obtain the phase boundaries for the emergence of
orientational order in the considered systems. Our results provide insights
into the phase behavior of biaxial nematic liquid crystals, and in particular
into methods for their analytical investigation
Network topology of interlocked chiral particles
Self-assembly of chiral particles with an L-shape is explored by Monte-Carlo
computer simulations in two spatial dimensions. For sufficiently high packing
densities in confinement, a carpet-like texture emerges due to the interlocking
of L-shaped particles, resembling a distorted smectic liquid crystalline layer
pattern. From the positions of either of the two axes of the particles, two
different types of layers can be extracted, which form distinct but
complementary entangled networks. These coarse-grained network structures are
then analyzed from a topological point of view. We propose a global charge
conservation law by using an analogy to uniaxial smectics and show that the
individual network topology can be steered by both confinement and particle
geometry. Our topological analysis provides a general classification framework
for applications to other intertwined dual networks.Comment: 11 pages, 11 figure
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