| "Soft matter" was named firstly by de Gennes,the winner of Nobel Prize in physics.After that,soft matter is known and attracts much attention."Soft matter" is also named as "Soft condensed matter" or "Complex fluid",which is a kind of complex material between the ideal fluid and solid.Generally soft matter is composed of the large-molecule or group(solid,liquid,gas),which is much different from solid,liquid and gas.Thermal fluctuation of fluid and solid constraints cause the new behavior in soft matters,which exhibits the complexity and particularity of composition,structure and interaction of soft matters.In nanometer scale to microns (1～1000nm) range,soft matter can form a series of structures and dynamic systems, from simple sequences in space or time to complex organisms through the interaction.Soft matter is closely related with people's life,such as rubber,synthetic fiber, detergent,drugs and cosmetics,etc.Soft matter is widely used in the technology,such as LCD,polymers.Organisms is composed of soft material basically,such as cell, protein,etc.For the rich connotation and various application,soft matter attracts more and more attention of physicists,and has become an important research frontiers in condensed matter physics.The study of soft matter relates to many fields.We will focus on the related study in the application of colloidal crystals and electrorheological fluid.The following are our research work in soft matters.In Chapter 2,we exploit theoretically nonlinear optical materials by graded multilayered colloidal crystals,whose basic layer is made of metallodielectric nanoparticles immersed periodically in a host fluid.The properties of each layer can vary gradually within layers.We study the effective nonlinear optical response and the electric field distribution by both the analytical method and numerical method.The study shows that this analytical method agrees very well with an existing numerical method.The electric field distribution can be shown to exhibit a peak in a certain layer,and that the position of the peak can change by tuning the incident angular frequency.Such a gradationcontrolled electric field distribution serves as a physical mechanism for understanding the enhanced nonlinear optical responses with a broad plasmon band.In Chapter 3,by utilizing the electrorheological effect,three-dimensional col- loidal crystals can be produced,whose lattice structure can be changed from the body-centered -tetragonal lattice to other lattices under the application of electric fields.We calculate photonic band structures of such crystals with lattice structure transformation, and demonstrate the existence of complete band gaps for some intermediate lattices. Thus,it becomes possible to use the electrorheological effect to achieve photonic crystals with desired photonic gap properties resulted from tunable structures.In Chapter 4,the optical responses of coupled metal nanoparticles are studied. Muti-mirrors method has been used to consider the coupling interaction between particles. For two same particles,there are two plasmon resonant frequencies,and the small one is caused by the coupling interaction between particles.For two unequal nanoparticles,the small particles can have a much shift of plasmon resonant frequency, which depends on the mutual interaction between two particles,while the big particles is not sensitive to the coupling interaction between particles.The plasmon resonance becomes stronger as the two particles become closer.At very close distance,the plasmon resonant peak of the coupling interaction is much larger than one of the single particle for the small particle.The results exhibit that the plasmon resonance can be tuned by the electromagnetic coupling between neighboring particles,which will have application in future.
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