Controlling the Orientation of Micron-Sized Rod-Shaped SiC Particles with Nematic Liquid Crystal Solvents

The orientational behavior of micron-sized rod-shaped SiC particles in the liquid crystal (LC) solvents E7, N-(4-methoxybenzylidene)-4-butylaniline (MBBA), and 4 -octyl-4ʹ-cyanobiphenyl (8CB) has been studied. Particles were observed to predominately orient either parallel or perpendicular to the nematic director, with an equilibrium orientation depending on their surface chemistry and choice of LC solvent. In two cases, a bimodal distribution of particle orientations was found, with a minority population of particles adopting an orientation orthogonal to the majority one. Longer particles were slightly better oriented than shorter ones. No temperature dependence on particle orientation was observed up to the clearing point. Successive deposition of particles onto a solid substrate with different equilibrium orientations controlled through choice of the LC was shown to be effective for producing films with alternating particle arrangement between layers. Taken together these findings demonstrate that liquid crystals can provide a versatile means for solution-phase assembly of ordered films comprised of micron- and submicronsized rod-shaped building blocks.