Critical Phonema In Composit Media

University Of Utah, Salt Lake City UT

Investigators

Abstract

A scientifically and technologically important class of composite materials are those which exhibit a sharp transition in their material and microstructural properties as some parameter is varied near a critical point. One example with extremely rich behavior is an electrorheological (ER) fluid, which is a colloidal suspension of polarizable particles of high complex dielectric constant, with typical sizes ranging from micron to millimeter scales, in a viscous fluid of low complex dielectric constant such as oil. The application of a strong electric field to such a suspension produces within milliseconds a dramatic transition from an oily slurry to a solid-like state with an increase in the viscosity of the suspension by many orders of magnitude. For non-conducting dielectric spheres, the transition is characterized by the formation of chains which aggregate into columns parallel to the field. For metal spheres, net-like structures with fractal characteristics form. Recently the investigator has introduced a way of applying the methods of statistical mechanics to macroscopic problems in composite media, for length scales much larger than the in the traditional domain of statistical mechanics. In the research supported by this award, the investigator will develop these methods further and begin applying them to study the critical properties of ER fluids, particularly those with larger spheres where thermal effects are negligible, and classical application of statistical mechanics yields little information. Materials such as electrorheological (ER) fluids which exhibit some type of marked transitional behavior appear throughout science and engineering, and are important in many technological applications. Other examples include sea ice, porous media such as sandstones and soils, particulate composites used in smart devices and in conducting films for electromagnetic applications, and material failure due to fracture. The fluid/solid transition in ER fluids is a particularly interesting example of the type of critical behavior exhibited by these materials. The potential for rapid electrical control of rheological properties has attracted considerable attention to ER fluids, with applications including clutches, pumps, brakes and shock absorbers. From a theoretical standpoint, however, there remains much to be understood about the material behavior and properties near the transition. In the proposed work the investigator will develop mathematical methods for understanding the transition in ER fluids, as well as other composite materials exhibiting critical behavior.