Self-assembly Of Colloidal Droplets,Gold Nanorods And Aggregation-induced Emission Dyes In Liquid Crystals And Its Optical Characterizations

The phrase "things gather together and people gather in groups" reveals that things and people always combine and act according to certain rules,which is the meaning of self-assembly.Self-assembly is ubiquitous in nature,such as how atoms and molecules constitute macroscopic substances,crystal growth,formation of various organisms and so on.People use self-assembly to make materials spontaneously form the structure people expect,which is a very desirable thing.Among various self-assembly methods,liquid-crystal-mediated method is simple and excellent.Because the structure of liquid crystals have a different degree of order,and there is anisotropic elastic force in liquid crystals,where foreign objects are self-assembled into various ordered structures due to the elasticity of the liquid crystals.This thesis studies the self-assembly of various foreign objects in liquid crystals.The research in this thesis is divided into the following three parts according to the size of foreign objects:The first part is the self-assembly of micro-and sub-micron-sized colloidal droplets in liquid crystals.The colloidal droplets in the liquid crystal are affected by the anisotropic elastic force and can either form colloidal crystals or bifurcation structures with fractal characteristics.The causes of various structures of colloidal droplets can be explained by the analog of the concepts of dipole moment and quadrupole moment in electrostatics.The various ordered structures formed by the colloidal droplets help one understand how atoms and molecules combine with each other to form complex structures through electrostatic interaction.The second part is the self-assembly of gold nanorods whose size is several tens of nanometers in the liquid crystals.The use of liquid crystals as a medium to arrange nanorods in a large area in a specific manner is a way to realize the self-assembly of nanorods.Arranging gold nanorods into specific structures can produce optical metamaterials,such as materials with negative refractive index,hyper-lenses,optical cloaking and so on.In this thesis,the self-assembly of gold nanorods in lyotropic liquid crystals and thermotropic liquid crystals is studied.Nanorods are arranged into a variety of structures.Nanorods in thermotropic liquid crystals can also be tuned by an external electric field.The third part is the self-assembly of organic dye molecules in liquid crystals,whose typical example is dye-doped liquid crystal lasers.Aggregation-induced emission dyes are used herein as a gain medium for liquid crystal lasers.Combining the characteristics of the aggregation-induced emission dye with the defect structures in the liquid crystals solves the problem of aggregation-caused quenching,which exists in the system of conventional dyes and liquid crystals.At the same time,using aggregation-induced emision dyes as the gain medium for liquid crystal lasers improves the resistance of photo bleaching.