Ordering and motion of anisotropic nanomaterials
Doctor of Philosophy
Multi-scale ordering of the components is of utmost importance for the preparation of any functional system. This is particularly interesting for the assembly of plamonic nanoparticles which show drastic differences in their optical properties compared to the individual counterparts, giving rise to the unique opportunity to perform enhanced spectroscopies, sensing, and transporting optical information below the diffraction limitation of light. The control over ordering of nanoscale materials is therefore of paramount importance. Template based bottom up approaches such as using nematic liquid crystals promise a long range, reversible ordering of nanomaterials. It also promises active control over plasmonic properties of metal nanoparticles due to the electric field induced reorientation of liquid crystals, resulting in a change of the local refractive index. This thesis discusses the possibility of ordering anisotropic metal nanoparticles and performing active modulaton of the plasmonics response using a nematic liquid crystals. While long polymer chains can be solvated and aligned in liquid crystal solvents, anisotropic metal nanoparticles could not be dissolved in the nematic liquid crystal phase because of their poor solubility. Here, I show that appropriate surface functionalization can increase the otherwise low solubility of plasmonic nanoparticles in a nematic liquid crystal matrix. I also show that it is possible to reversibly modulate the polarized scattering of individual gold nanorods through an electric field induced phase transition of the liquid crystal. In this thesis, I also studied the motion of a molecular machine, commonly known as nanocars, over different solid surface. I show that individual nanocars, which consist of four carborane wheels attached to an aromatic backbone chassis, can move up to several micrometers over a glass surface at ambient temperature. Their movement is consistent with the rolling of the carborane wheels and can be controlled by tuning the interaction between the surface and the wheels.