Interactions between particles and liquid crystals: Local ordering and driven assembly

The research presented in this thesis explores the interactions between nanoparticles and microparticles and nematic liquid crystals (LCs). The primary motivation for this study was to investigate the possibility of using interparticle interactions mediated by LCs to drive nanoparticles dispersed in LCs into ordered assemblies. As a first step towards realizing LC-directed assembly of nanoparticles, an approach was devised to study: (1) the interactions between LCs and immobilized nanoparticles to verify that surface chemistry could be used to control the ordering of LCs near the surfaces of gold nanoparticles, (2) the assembly of microparticles in LCs, to understand the forces and structures that result when particles interact due to forces imposed by the nematic LC, and (3) the mobility and interactions of nanoparticles dispersed in LCs. In contrast to the existing literature on microparticles dispersed in LCs, studies on nanoparticles in LCs are rare, due in large part to the limited spatial resolution of the techniques used to probe the interactions between microparticles in LCs (optical microscopy) and the difficulties encountered with dispersing particles into LCs in general. In the research described in this thesis, we present studies that probe the nanoscopic dielectric environment surrounding immobilized gold nanoparticles immersed in nematic LC by taking advantage of the inherent optical properties of the gold nanoparticles. We then probe the nanoscopic mechanical environment surrounding gold nanoparticles dispersed in nematic LC by tracking the motions of isolated gold nanoparticles as well as pairs of gold nanoparticles. Finally, we present studies of the directed, dynamic, and reversible assembly of microparticles at the interface of a nematic LC and an isotropic liquid by taking advantage of the forces provided by the nematic LC.