Several Complex Fluid Properties

"Soft matter" was named firstly by P. G. de Gennes, the winner of Nobel Prize in 1991, and physical scientist in France. "Soft matter" is also called "Complex fluid" "Soft matter" or "Soft condensed matter" is a kind of complex system between the ideal fluid and solid. Generally, soft matter is composed of group (solid, liquid, gas) or the large-molecule. The interaction between building blocks is week (about KT), so the thermal fluctuation and entropy control the motion of the system. This kind of materials is much different from solid, liquid and gas. Thermal fluctuation of fluid and the constraint of solid cause the new behavior in soft matter, which exhibits the complexity and particularity of composition, structure and interaction of soft matter.The 21st century is considered as the century of life sciences, from the point of view of matter division, this is also the century of soft matter. If there is no soft matter, life can not exist. Any biological structure (including DNA, proteins and biomembrane) are built on the basis of soft matter. For the peculiar behavior, rich physical connotation, and various applications, soft matter attracts more and more attention of physicists, and has become an important research direction with challenge and urgency, and an important research frontier in condensed matter physics. We mainly investigate the structures, properties, and applications of some complex fluids, such as ferrofluids, inverse ferrofluids, and electrorheological fluids. Then, we introduce the concept and some applicatios of metamaterials and soft metamaterials.In Chapter 2, we numerically demonstrate optical negative refraction by using finite element simulations in ferrofluids containing isotropic Fe3O4 nanoparticles, each hav-ing an isotropic Ag shell suspended in water, in the presence of an external dc magnetic field H. Under external magnetic field, the particles will form chains, as the magnetic increases, the chains will form columns. The all-angle broadband optical negative re-fraction with magnetocontrollability arises from H-induced chains or columns. They result in hyperbolic equifrequency contour for transverse magnetic waves propagating in the system. From the boundary conditions, we found that the refraction of energy is negative. The proposed concept of soft optical matamaterials add us an external free-dom (external fields) to control the structure of the materials, so the optical properties of the materials will change as the external field change. Besides, we introduce the theory about multifrequecy optical cloak. On the basis of transformation optics and metamaterials, we can design some optical devises, which can arbitrarily manipulate electromagnetic field. In real applications, the absorption of the materials is big. We can use the gain materials to compensate for loss. Another challenge is to extend the working band at high frequencies.In Chapter 3, we investigate the ground state and magnetophoresis of inverse fer-rofluids. We found that the ground state of inverse ferrofluids is body-centered tetrag-onal (bct) lattices by using the dipole-multipole interaction model. Understanding the ground state of the system, we can further investigate the basic properties of the sys-tem. On the basis of the Ewald-Kornfeld formulation and the Maxwell-Garnett theory, we theoretically investigate the magnetophoretic force exerting on the nonmagnetic particles in inverse ferrofluids due to the presence of a nonuniform magnetic field, by taking into account the structural transition and long-range interaction. We numerically demonstrate that the force can be adjusted by choosing appropriate lattices, volume fractions, geometric shapes, and conductivities of the nonmagnetic particles, as well as frequencies of external magnetic fields. Magnetophoresis has been widely used in mill run and separation of biological cells. Our results have some significance in practical application of magnetophoresis.In Chapter 4, taking into account the multipole interaction, we utilize three methods to investigate the dynamic behavior of a chain of three microparticles in an electric field, two of which are fixed and symmetrically located in the two opposite sides of the third free microparticle. We reveal that, if the free microparticle is laterally dragged and released, it can oscillate perpendicular to the line joining the centers of the two fixed microparticles, being in simple harmonic oscillation with a fixed period for small oscillation amplitudes. The period of the harmonic oscillation can be controlled by the permittivity, density, radius, the distance of the particles, as well as the external electric field. Our results help us to understand the mechanism of the interaction of the particle chains in complex fluids under external fields.