The Study Of Self-assemblies Of Plasmonic Nanoparticles In Liquid Crystals And Their Optical Properties

Self-assembly of nanoscale building blocks into long-range three-dimensional (3D) structures is key to the development of nanostructured materials with preengineered optical properties. Liquid crystals (LCs) combine fluidity with long-range orientational ordering and thus are promising host media for organizing micro-and nanosized colloids into long-range ordered structures. In this paper we studied the bulk self-assembly of dispersed plasmonic nanoparticles with long-range order by LCs matrix because LCs as "smart fluid hosts"’impose various degrees of orientational or positional ordering, serve as bulk fluid templates for colloidal self-organization and can easily response to external stimuli such as electrical and magnetic field. Details are as following:First, dispersing of nanoparticles into LC host is a great challenge in this field. In this work we achieved a stable plasmonic nanoparticles-LC composites with high concentration. We studied the self-assembly of plasmonic nanoparticles with positive as well as negative order parameters in LC with different liquid crystalline phases such as nematic, cholesteric, hexagonal and lamellar phase.Second, we explored the physics of the interaction of plasmonic nanoparticles with the building blocks of LCs. We proposed a model to explain the alignment of nanoparticles with positive as well as nagnetic order parameters in LC host based on anisotropic surface anchoring interactions of nanorods with the structured host medium. Self-alignment and effective-medium optical properties of these hybrid inorganic-organic complex fluids match predictions of our model. In addition, we applied the Onsager theory to study the alignment of nanoparticles in cellulose nanocrystal LC and the partial mixing phenomenon of nanoparticles in LC host.Third, we measured the distinctive optical properties of plasmonic nanoparticles in LC host. The aligned nanoparticles results in a strong polarization sensitivity of localized surface plasmon resonance (SPR) effects exhibited by the nanostructured composite medium, which shows polarization-dependent extinction, scattering and two-photon luminescence, exhibiting stark differences from that of the same nanoparticles in isotropic fluids.This work shows the potential for LC-mediated oriented self-assembly of nanomaterials as a tool for mass production of bulk optical metamaterials and plasmonic optical components with tunable and switchable properties.