Direct observation of interaction of nanoparticles in a nematic liquid crystal

The topological properties and interactions of nano colloids in the nematic liquid crystal pentylcyanobiphenyl (5CB) have been studied. We find that silica particles, surface-functionalized with N,N-dimethyl-N-octadecyl-3-aminopropyl trimethoxysilyl chloride induce a dipolar structure of 5CB around them even for 125 nm diameter colloids. The 125 nm dipolar colloidal particle is accompanied by a clearly resolvable hyperbolic point defect and behaves hydrodynamically as a much bigger particle because of the elastic distortion around it. This has a surprising consequence that the pair-binding energy of the dipolar nanocolloids is as high as 700 k(B)T for 125 nm colloids and is practically size-independent in the range from 125 nm to 500 nm.