What happens if you put something into a liquid crystal...

We study the phase ordering colloids suspended in a thermotropic nematic liquid crystal below the clearing point Tni and the resulting aggregated structure. Small PMMA particles are dispersed in a classical liquid crystal matrix, 5CB or MBBA. We show that small colloid particles densely aggregate on thin interfaces surrounding large volumes of clean nematic liquid, thus forming an open cellular structure, with the characteristic size of 10-100 micron inversely proportional to the colloid concentration.
Small colloid particles dispersed in a liquid crystal matrix densely pack on cell interfaces, but reversibly mix with the matrix when the system is heated above Tni.
Rheological study of cellular structures gives remarkably high elastic modulus, G' > 0.1 MPa, which is a nearly linear function of particle concentration. A characteristic yield stress is required to disrupt the continuity of cellular structure and liquify the response. These findings are supported by theoretical arguments based on the Landau mean-field treatment, continuous phase separation and the granular collapse mechanism of cellular wall formation. High surface tension of walls arises from the local melting of nematic liquid and the depletion locking of packed particles on interfaces.

We use a Monte Carlo algorithm to simulate the director field around a spherical inclusion in a uniform nematic liquid crystal matrix. The resulting structure crucially depends on the relative strength of the nematic bulk elasticity and the director anchoring on the particle surface. When this anchoring is weak, the director field perturbations are small and have quadrupolar symmetry. With increasing effective strength of anchoring, given by the non-dimensional parameter WR/K, two topologically non-trivial situations are possible: a dipolar configuration with a satellite point defect (hedgehog) near the particle pole, or a quadrupolar configuration with a ``Saturn ring'' of disclination around the particle equator.

Long-range forces and aggregation of colloid particles in a nematic liquid crystal
Phys. Rev. E55, 2958 (1997). (PDF-file downloadable)

We calculate the long-range pair potential of interaction between spherical colloid particles suspended in a uniform liquid crystal. Independently on the strength, or type of director anchoring on particle surface, the far-field director distortions decays as r^{-3} sin 2\theta. This leads to an anisotropic interaction potential of the form U ~ d^{-5} with d the distance between two colloid particles. This non-central potential gives strong repulsion for particles along the director axis, weak repulsion for particles located in the perpendicular plane, and attraction at oblique angles. When an external H-field is applied, the director decays exponentially away from the particle and, hence, interaction forces are short-range.

Friction Drag on a Particle Moving in a Nematic Liquid Crystal
Phys. Rev. E54, p.5204 (1996).

The flow of a liquid crystal around a particle does not only depend on its shape and the viscosity coefficients but also on the direction of the molecules. We studied the resulting drag force on a sphere moving in a nematic liquid crystal in a low Reynold's number approach for a fixed director field (low Ericksen number regime) using the computational artificial compressibility method. Taking the necessary disclination loop around the sphere into account, the value of the drag force anisotropy for an exactly computed field is in good agreement with experiments (~1.5) done by conductivity diffusion measurements. We also present data for weak anchoring of the molecules on the particle surface and of trial fields, which show to be sufficiently good for most applications. Furthermore, the behaviour of the friction close to the transition point nematic-isotropic and for a rod-like and a disc-like liquid crystal will be given.

Stability of Liquid Crystalline Macroemulsions
Europhys. Lett. v.32, 607, 1995.

The topological stability of emulsions of liquid crystal in water-glycerol matrices is demonstrated for a wide range of materials and concentrations. Coalescence is prevented by an energy barrier for a topological ring defect formation in a neck between the two merging droplets. There is a characteristic size of emulsion droplets, typically tens of microns or more, controlled by the balance of elastic and anchoring energies of the liquid crystal. On removal of liquid crystallinity (by raising the temperature above T_{ni} in thermotropic nematic materials, for example) the energy barriers for coalescence disappear and emulsion droplets can merge quickly, controlled only by the traditional kinetic effects.

We analyze the director field around a spherical colloid particle with radial (homeotropic) anchoring on its surface. Depending on the relative strength of effective anchoring, controlled by the key parameter WR/K with R the particle radius, the director distribution may possess a singular "Saturn ring" of a (-1/2) disclination in the equatorial plane. The equilibrium radius of this ring, at rigid radial anchoring, is a* ~ 1.25R and only weakly depends on the disclination core energy. At small anchoring the director field is regular and weakly disturbed by the particle, there is a characteristic crossover anchoring W* between the two regimes. We obtain the interpolated analytical expression for n(r), which decays as r^{-3} sin 2\theta away from the particle, and compare it with the exact numerical solution in the highly distorted non-linear regime.

The fluctuation spectrum of membranes in nematic solvents is altered by the boundary condition imposed on the bulk nematic director by the curved membrane. We discuss some properties of single and multi-membrane systems in nematic solvents, primarily based on the Berreman-de~Gennes model. We show that: membranes in nematic solvents are more rigid and less rough than in their isotropic counterparts; have a different Helfrich steric stabilization energy, proportional to d^{-3}, and hence a different compression modulus in the lamellar state; and can exhibit phase separation via unbinding during a quench into the nematic state. We also discuss the preparation and possible experimental effects of nematic-mediated surfactant membrane system.

Here is some "ancient" stuff, which is still very close to my heart:

By extending statistical theory of the rheological properties of nematics we derive elementary expressions for all phenomenological viscosity coefficients of ferroelectric smectics C* in terms of a small number of parameters. The results permit estimates of signs and ratios of the viscosity coefficients and their tilt angle dependence. It is shown that a number of coefficients generally appear to be very small and can be neglected in practical calculations. We discuss also the influence of molecular biaxiality on the rotational viscosity of smectics C.

A ferroelectric instability is predicted to occur in an experimentally accessible temperature range in a main-chain (semiflexible) liquid crystalline polymer with directed polar mesogenic segments. The long-range part of the dipole-dipole interaction is separated and its effect is completely accounted for in the average electric field. The remaining (local) free energy density is derived in the form of an expansion in powers of the spontaneous polarization. We derive simple expressions for the instability temperature and the polar mean-field coupling in a polar nematic polymer in terms of the molecular model parameters. Using simple estimates we show that ferroelectric ordering is more likely to occur in nematic polymers with directed polar segments than in low molecular weight nematic liquid crystals composed of polar molecules.

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