Force between colloidal particles in a nematic liquid crystal studied by optical tweezers
Kenji Takahashi, Masatoshi Ichikawa, and Yasuyuki Kimura

We measure the dependence of the interparticle force $F$ on the distance $R$ between two colloidal particles with hyperbolic hedgehog defects in a nematic liquid crystal using optical tweezers. The particle-defect pair can be regarded as an elastic ``dipole'' in the electrostatic analogy. In a parallel configuration, where the dipole vectors are parallel with each other, $F$ is attractive and proportional to $R^{-4}$. However, $F$ becomes repulsive at small $R$ due to the existence of a defect between the particles. In an antiparallel configuration, where the particles directly face each other, $F$ is repulsive over the whole range of $R$ and proportional to $R^{-3.6}$. In another antiparallel configuration, where two hyperbolic hedgehog defects directly face each other, $F$ is proportional to $R^{-3.6}$, and $F$ at small $R$ turns out to be attractive upon tilting the dipoles. Furthermore, we yield the force between particles connected by a stringlike defect called a bubble-gum defect.\

© 2008 The American Physical Society.