20,815 research outputs found
Imbibition in mesoporous silica: rheological concepts and experiments on water and a liquid crystal
We present, along with some fundamental concepts regarding imbibition of
liquids in porous hosts, an experimental, gravimetric study on the
capillarity-driven invasion dynamics of water and of the rod-like liquid
crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers
across in monolithic silica glass (Vycor). We observe, in agreement with
theoretical predictions, square root of time invasion dynamics and a sticky
velocity boundary condition for both liquids investigated.
Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the
existence of a paranematic phase due to the molecular alignment induced by the
pore walls even at temperatures well beyond the clearing point. The ever
present velocity gradient in the pores is likely to further enhance this
ordering phenomenon and prevent any layering in molecular stacks, eventually
resulting in a suppression of the smectic phase in favor of the nematic phase.Comment: 18 pages, 8 figure
Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids
In this review, we describe and analyze a mesoscale simulation method for
fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now
called multi-particle collision dynamics (MPC) or stochastic rotation dynamics
(SRD). The method consists of alternating streaming and collision steps in an
ensemble of point particles. The multi-particle collisions are performed by
grouping particles in collision cells, and mass, momentum, and energy are
locally conserved. This simulation technique captures both full hydrodynamic
interactions and thermal fluctuations. The first part of the review begins with
a description of several widely used MPC algorithms and then discusses
important features of the original SRD algorithm and frequently used
variations. Two complementary approaches for deriving the hydrodynamic
equations and evaluating the transport coefficients are reviewed. It is then
shown how MPC algorithms can be generalized to model non-ideal fluids, and
binary mixtures with a consolute point. The importance of angular-momentum
conservation for systems like phase-separated liquids with different
viscosities is discussed. The second part of the review describes a number of
recent applications of MPC algorithms to study colloid and polymer dynamics,
the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of
viscoelastic fluids
Dielectric Hysteresis, Relaxation Dynamics, and Non-volatile Memory Effect in Carbon Nanotube Dispersed Liquid Crystal
The self-organizing properties of nematic liquid crystals (LC) can be used to
template carbon nanotubes (CNTs) on a macroscopic dimension. The nematic
director field, coupled to the dispersed CNT long-axis, enables controlled
director reorientation using well-established methods of LC alignment
techniques, such as patterned-electrode-surface, electric fields, and magnetic
fields. Electric field induced director rotation of a nematic LC+CNT system is
of potential interests due to its possible applications as a nano
electromechanical system. The relaxation mechanism for a LC+CNT composite, on
the removal of the applied field, reveals the intrinsic dynamics of this
anisotropic system. Dielectric hysteresis and temperature dependence of the
dielectric constant coherently shows the ferroelectric-type behavior of the
LC+CNT system in the nematic phase. The strong surface anchoring of LC
molecules on CNT walls results in forming local isolated pseudo-nematic domains
in the isotropic phase. These domains, being anisotropic, respond to external
fields, but, do not relax back to the original state on switching of the field
off, showing non-volatile memory effect.Comment: 7 pages, 8 figure
Novel mid-infrared dispersive wave generation in gas-filled PCF by transient ionization-driven changes in dispersion
Gas-filled hollow-core photonic crystal fibre (PCF) is being used to generate
ever wider supercontinuum spectra, in particular via dispersive wave (DW)
emission in the deep and vacuum ultraviolet, with a multitude of applications.
DWs are the result of the resonant transfer of energy from a self-compressed
soliton, a process which relies crucially on phase matching. It was recently
predicted that, in the strong-field regime, the additional transient anomalous
dispersion introduced by gas ionization would allow phase-matched DW generation
in the mid-infrared (MIR)-something that is forbidden in the absence of free
electrons. Here we report for the first time the experimental observation of
such MIR DWs, embedded in a 4.7-octave-wide supercontinuum that uniquely
reaches simultaneously to the vacuum ultraviolet, with up to 1.7 W of total
average power
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