Dispersion and self-assembly of anisotropic plasmonic nanoparticles in liquid crystalline media.

摘要

Noble metal nanoparticles possess extraordinary optical properties due to their plasmon modes that make them desirable for inclusion into materials. Non-dipolar plasmon modes are one of the simplest known ways to control the magnetic properties of a material; consequently gold nanoparticles are one of the most promising systems to produce metamaterials. In order to fully utilize the properties of gold nanoparticles for device applications, one needs to control the interparticle spacing, distribution, and orientation of anisotropic gold nanoparticles within a material. Liquid crystalline host materials can allow for alignment and self-assembly of nanoparticles through viscoelastic forces. In this thesis, I demonstrate the feasibility of incorporating nanoparticles into liquid crystals and assembling complex architectures through elasticity mediated interaction.;First, we explore the dispersion of nanoparticles of various size and shape in a few different liquid crystalline systems. 20nm thick gold nanorods can be dispersed at reasonably high concentrations in micellar lyotropic systems, but show qualitatively different self-assembly behavior depending on their length. 10 micron wide, 5nm thick polygonal platelets produce elastic distortions in thermotropic and lyotropic systems, while behaving like "molecular" inclusions in a graphene oxide based discotic phase.;Next, we look at the elastic interactions between colloids of various shapes and sizes and topological defects. Homeotropically aligned glass microspheres produce a hyperbolic hedgehog point defect or Saturn ring which attract and align nanoparticles in different manners depending on the surface chemistry, size and shape of the nanoparticle. We have also optically generated topological defects in frustrated cholesteric cells which contain similar hyperbolic hedgehog point defects that eliminates the need of microsphere inclusions. We have produced elastomeric cylinders with photothermal response enhanced by gold nanospheres that allow for an arbitrary particle shape to be generated in situ to explore the rich physics associated with arbitrary nematostatic and cholesterostatic dipoles.;This work extends our understanding of colloidal inclusions in liquid crystals to the regime where the mesogen size and colloidal inclusion have sizes within a couple orders of magnitude of each other and potentially allows for the development of an exciting new class of nanocomposite liquid crystalline materials.