952 research outputs found
Ordering dynamics of blue phases entails kinetic stabilization of amorphous networks
The cubic blue phases of liquid crystals are fascinating and technologically
promising examples of hierarchically structured soft materials, comprising
ordered networks of defect lines (disclinations) within a liquid crystalline
matrix. We present the first large-scale simulations of their domain growth,
starting from a blue phase nucleus within a supercooled isotropic or
cholesteric background. The nucleated phase is thermodynamically stable; one
expects its slow orderly growth, creating a bulk cubic. Instead, we find that
the strong propensity to form disclinations drives the rapid disorderly growth
of a metastable amorphous defect network. During this process the original
nucleus is destroyed; re-emergence of the stable phase may therefore require a
second nucleation step. Our findings suggest that blue phases exhibit
hierarchical behavior in their ordering dynamics, to match that in their
structure.Comment: 11 pages, 5 figures, 2 supplementary figures, 2 supplementary tables,
accepted by PNA
Colloidal Jamming at Interfaces: a Route to Fluid-bicontinuous Gels
Colloidal particles or nanoparticles, with equal affinity for two fluids, are
known to adsorb irreversibly to the fluid-fluid interface. We present
large-scale computer simulations of the demixing of a binary solvent containing
such particles. The newly formed interface sequesters the colloidal particles;
as the interface coarsens, the particles are forced into close contact by
interfacial tension. Coarsening is dramatically curtailed, and the jammed
colloidal layer seemingly enters a glassy state, creating a multiply connected,
solid-like film in three dimensions. The resulting gel contains percolating
domains of both fluids, with possible uses as, for example, a microreaction
medium
Bulk rheology and microrheology of active fluids
We simulate macroscopic shear experiments in active nematics and compare them
with microrheology simulations where a spherical probe particle is dragged
through an active fluid. In both cases we define an effective viscosity: in the
case of bulk shear simulations this is the ratio between shear stress and shear
rate, whereas in the microrheology case it involves the ratio between the
friction coefficient and the particle size. We show that this effective
viscosity, rather than being solely a property of the active fluid, is affected
by the way chosen to measure it, and strongly depends on details such as the
anchoring conditions at the probe surface and on both the system size and the
size of the probe particle.Comment: 12 pages, 10 figure
Bijels Containing Magnetic Particles: A Simulation Study
Bicontinuous, interfacially jammed emulsion gels (bijels) represent a class
of soft solid materials in which interpenetrating domains of two immiscible
fluids are stabilized by an interfacial colloidal monolayer. Such structures
can be formed by arrested spinodal decomposition from an initially single-phase
colloidal suspension. Here we explore by lattice Boltzmann simulation the
possible effects of using magnetic colloids in bijels. This may allow
additional control over the structure, during or after formation, by
application of a magnetic field or field gradient. These effects are modest for
typical parameters based on the magnetic nanoparticles used in conventional
ferrofluids, although significantly larger particles might be appropriate here.
Field gradient effects, which are cumulative across a sample, could then allow
a route for controlled breakdown of bijels as they do for particle-stabilized
droplet emulsions
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