International Research Fellowship Program: Morphological Instability in Freezing Colloidal Suspensions

Anderson Anthony M, Chicago IL

Investigators

Abstract

0965138 Anderson The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. Anthony Anderson to work with Dr. Grae Worster at the University of Cambridge (DAMTP) in the United Kingdom. Colloidal suspensions do not freeze uniformly. Instead, the frozen phase (e.g. ice) becomes segregated, trapping bulk regions of the colloid within, and a fascinating variety of patterns in the structure of the segregated ice emerge. These patterns depend on the freezing condition, particle concentration, and other properties of the colloidal suspension. Recent efforts by Prof. Worster and his collaborators to model the freezing of hard-sphere colloidal suspensions demonstrate that a planar ice interface can become thermodynamically unstable and break down spatially during solidification. The central aim of the current investigation is to identify the extent to which this thermodynamic mechanism for morphological instability underlies pattern formation in colloidal systems in general. The investigation relies on a combination of theory and experiments. The Directional Solidification facility housed in DAMTP at the University of Cambridge is being used to perform the necessary experimental tests of the theoretical predictions of morphological transitions. This combination of mathematical analysis and experimentation has proven to be a very powerful approach in the development of the theory of alloy solidification, which shares several analogous features with the solidification of colloidal suspensions. Many natural and technological processes involve the solidification of particle suspensions. In particular, ?freeze-casting? technology relies on the patterns of segregated ice as templates for engineering advanced composite materials. The phenomenon of ice segregation also underlies frost heave, whereby saturated soils expand as they freeze, which can lead to beautifully patterned ground, but cause damage to engineering structures. Other examples of interest include the preservation of cells, tissues, and perishable foods. The development of a theory to predict the conditions under which various patterns occur will consequently impact several applications.