Several Material Properties Of Soft Matter Research

Soft matter is a hot research area in recent years. Their behavior is mostly in be-tween solid and ideal liquid material. Two of the major features are complexity and flexibility. They include liquids, colloids, polymers, foams, gels, granular materials and so on. A typical property of soft matter is a very mild chemical action has induced a drastic change in mechanical properties. Also entropy plays an important part in the soft matter. They can be easily found in our daily life, such as rubber, ink, washing detergent, milk and cosmetics; our human body is also built of the soft matter, like the cell, protein, DNA and RNA. Their peculiar behaviors, undiscovered mechanism and potential applications have already draw much attentions. In this way, soft matter is still a challenging research area.In this dissertation, we introduce our theoretical study of the properties of soft mat-ter. It includes, the nonlinear optical response of the colloidal crystals, the second harmonic generation with magnetic-filed controllabilities based on the ferrofluids, the optical properties of the photonic crystal by using the ferrofluids, the dielectrophoresis of an inhomogeneous particle under an inhomogeneous field of an oscillating dipole moment, the study of thermal and dielectric properties of the shaped graded material.This paper is organized as follows:in the first chapter, we shall give an introduction of soft matter, which include the development and the properties of soft matter. We mainly give an overview of the colloid crystals, ferrofluids. The graded material will also be introduced.In the second chapter, based on the Ewald-Kornfeld formulation, we study the effec-tive third-order nonlinear optical susceptibilities for non-degenerate four-wave mixing and third-harmonic generation in colloidal crystals, which are made of graded metal-lodielectric nanoparticles suspended in a host fluid. Theoretical results show that both an enhancement and a red shift of the optical nonlinearity in such colloidal crystals appear due to the effects of local fields and lattice structure. And the presence of the dielectric gradation is helpful to achieve large enhancement of nonlinearity at low fre-quencies. Then we study the effective susceptibility of second-harmonic generation (SHG) in colloidal crystals. We also find a large enhancement and red shift of SHG responses. The optimization of the Ewald-Kornfeld formulation is also investigated.In the third chapter, we theoretically exploit a class of nonlinear optical materials, which are made of single domain ferromagnetic nanoparticles coated by a nonmag-netic nanoshell with an intrinsic second-harmonic generation SHG susceptibility in a nonmagnetic host fluid. The SHG of such materials possess magnetic-field controlla-bilities, i.e., magnetic-field-controllable anisotropy, redshift, and enhancement, which are caused to appear by the shift of a resonant plasmon frequency due to the formation of the chains of the coated nanoparticles. Then, by using the ferrofluid made of fer-romagnetic particles suspended in a host fluid, double layer photonic crystal structure (ferrofluid versus normal medium) is put forward. The influence of induced anisotropy by the applied magnetic field on the band structure has been considered. Theoretical re-sults show that precise tunability of the band gap can be obtained through the variation of the magnitude of the magnetic field.In the fourth chapter, we present a first-principles approach to dielectrophoresis of an inhomogeneous particle under an inhomogeneous field of an oscillating dipole mo-ment. In this approach, the particle can possess an arbitrary inhomogeneity profile as long as the radial equation can be solved, at least numerically. For numerical calcu-lation, we treat the inhomogeneous particle as a graded one with physically motivated dielectric model and conductivity profile. We find that the spatial fluctuations inside the particle can affect the dielectrophoretic spectrum of the particle significantly.In the fifth chapter, based on a first-principles approach, we exploit a class of shaped graded materials in which thermal energy is apparently controlled to transfer from a region of lower temperature to a region of higher temperature. This phenomenon, which is in contrast to our common intuition, is indicative of an apparent negative thermal conductivity (ANTC). Further analysis shows that the ANTC is related to a symmetric oscillation of paired thermal conductivities with specific gradation profiles, which are shown to satisfy a sum rule. Such shaped graded materials can serve as good candidates for thermal rectification. Then we investigate the pathway of electric displacement fields in shaped graded dielectric materials existing in the form of cloaks with various shapes. We reveal a type of apparently negative electric polarization (ANEP), which is due to a symmetric oscillation of the paired electric permittivities, satisfying a sum rule. The ANEP does not occur for a spherical cloak, but appears up to maximum as a:b (the ratio between the long and short principal axis of the spheroidal cloak) is about 5:2, and eventually disappears as a:b becomes large enough corresponding to a rod-like shape. Further, the cloaking efficiency is calculated for different geometrical shapes and demonstrated to closely relate to the ANEP.