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Colloidal Liquid Crystals

A colloid consists of a suspension of particles which are significantly larger than the molecules comprising the solvent. Colloidal liquid crystals are particularly interesting: the director orientation field of the solvent is distorted by the interaction with the macroparticle surface. Depending upon the details of this interaction, a topological defect in the director field, having the (idealized) form of a point, or an equatorial ring, is seen. This produces an effective interaction between macroparticles, mediated by the elastic deformation of the director.

Simulations enable us to study the nature of this interaction, although very large system sizes are required. In the upper snapshot on the right, two spherical macroparticles, each surrounded by a defect ring, interact with the nematic solvent and hence with each other. In the lower snapshot, we show the distorting effect of a rod-like macroparticle on the surrounding solvent; this produces a torque on the macroparticle, which may be measured, and a preferred alignment relative to the director.

D Andrienko, G Germano, M P Allen, Phys Rev E, 63, 041701/1-8 (2001)
D Andrienko, M P Allen, G Skacej, S Zumer, Phys Rev E, 65, 041702/1-7 (2002)
D Andrienko, M Tasinkevych, P Patricio, M P Allen, M M Telo da Gama,
Phys Rev E, 68, 051702/1-5 (2003)

The behaviour of macroparticles near the isotropic-nematic interface is currently of great interest.

J L West, A Glushchenko, G X Liao, Y Reznikov, D Andrienko, M P Allen,
Phys Rev E, 66 012702 (2002)
J L West, K Zhang, G X Liao, A V Glushchenko, Y Reznikov, D Andrienko, M P Allen,
Mol Cryst Liq Cryst, 410, 611 (2004)

two spherical macroparticles in a nematic solvent
rod-like macroparticle in a nematic solvent
Nematic solvent with macroparticles. We show director field streamlines and the order parameter is colour-coded (red=high, blue=low).