Dielectric composite materials

It has been observed in several studies that the use of organic monolayers or thin polymer phases to modify the surfaces of inorganic dielectric materials often improves the performance of these devices. This strategy has been employed for modification of Si02 [58] and AI2O3 surfaces [38] and more complicated dielectric composite materials. 

Cera.micA.bla.tors, Several types of subliming or melting ceramic ablators have been used or considered for use in dielectric appHcations particularly with quartz or boron nitride [10043-11 -5] fiber reinforcements to form a nonconductive char. Fused siHca is available in both nonporous (optically transparent) and porous (sHp cast) forms. Ford Aerospace manufactures a 3D siHca-fiber-reinforced composite densified with coUoidal siHca (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see COMPOSITE MATERIALS, CERAMIC MATRIX). 

The possibility of realizing via percolated w/o microemulsion conductor/insulating composite materials with very large dielectric constant and exotic optical properties has been pointed out [284],... 

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

Since the discovery of ordered mesoporous materials, researchers have explored many possible applications that can take advantage of the unique compositional or structural features of mesoporous materials. In addition to apphcations in traditional areas such as catalysis, separation, and ion exchange, new applications that might involve mesoporous materials include stationary phases in HPLC, bio and macromolecular separations, low dielectric constant materials, enzyme immobilization, optical host materials, templates for fabrication of porous carbons, and reactions in confined enviromnents. 

The dielectric breakdown problem can be solved very easily from the solution of the fuse problem in two dimensions using the concept of duality. This concept is largely used in the case of composite materials and in percolation for problems in d = 2 or with cylindrical symmetry (Mendelson 1975, Bowman and Stroud 1989). Here we follow the derivation of Bowman and Stroud. 

As mentioned earlier, suspensions of particulate rods or fibers are almost always non-Brownian. Such fiber suspensions are important precursors to composite materials that use fiber inclusions as mechanical reinforcement agents or as modifiers of thermal, electrical, or dielectrical properties. A common example is that of glass-fiber-reinforced composites, in which the matrix is a thermoplastic or a thermosetting polymer (Darlington et al. 1977). Fiber suspensions are also important in the pulp and paper industry. These materials are often molded, cast, or coated in the liquid suspension state, and the flow properties of the suspension are therefore relevant to the final composite properties. Especially important is the distribution of fiber orientations, which controls transport properties in the composite. There have been many experimental and theoretical studies of the flow properties of fibrous suspensions, which have been reviewed by Ganani and Powell (1985) and by Zimsak et al. (1994). 

Comparison of the properties of CSD thin films to the analogous bulk material properties has also received great attention because of the need for high dielectric constant materials for DRAM applications.Basceri et ai 134,135 jj yg thoroughly considered the differences between film and bulk properties from a fundamental perspective and have been able to interpret these differences in terms of stresses present in the films, compositional differences, and the impact of these characteristics on the phenomenological behavior of the material as predicted from a Landau-Ginzburg-Devonshire approach. All observed differences between film and bulk properties were explainable using this approach. 

Electroless deposition offers an attractive way of producing various fillers with a conductive surface or desirable magnetic properties, which can further be used in the production of composite materials with dielectric matrices for electromagnetic shielding. 

Spanoudaki, A., Pelster, R. Effective dielectric properties of composite materials The dependence on the particle size distribution. Phys. Rev. B 64, 064205 (2001)... 

Bergman, D. The dielectric constant of a composite material - A problem in classical physics. Phys. Rep. C 43, 377-407 (1978) Exactly solvable microscopic geometries and rigorous bounds for the complex dielectric constant of a two-component composite material. Phys. Rev. Lett. 44, 1285-1287 (1980)... 

Over the last decade, there has been considerable interest in the development of off-lattice models and theories describing percolation phenomena. Interest in percolation concepts has been spurred by the rather wide variety of applications for which such ideas are thought to be useful. These applications include the electrical conductivity and dielectric properties or permeability of composite materials, gelation, analysis of hydrogen bond networks, and reactions in porous catalysts. Recent progress in the development of off-lattice or, as they are most often called, continuum models of percolation began with the work of Coniglio et and Haan... 

Composite materials formed by nanometer-sized metal particles embedded in dielectrics have a growing interest o wing to the large values of fast optical Ken-susceptibility, whose real part is related to the intensity-dependent refractive index 2 [ ] Ion implantation has been shown to produce a high density of metal nanoparticles (MN) in glasses [2], The high-precipitate volume fraction and small size of MN leads to giant value of the [3]. This stimulates an interest in the use of ion implantation to fabricate nonlinear optical materials. 

Two types of Cu-nanoparticles-in-dielectric nanocomposites were produced through hydrogen reduction of Cu(II) Cu-zeolite and Cu-zeolite-silica. Amorphous silica was prepared by the sol-gel technique and served as optically transparent matrix incorporating zeolite microcrystals, The copper nanoparticles provide an optical response of the composite material due to the plasmon resonance band varied due to changes of matrix features. 

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