Dynamics of supercooled liquids and glasses: comparison of experiments with theoretical predictions

Abstract

Five years ago, preliminary light scattering studies in our laboratory of the mixed-salt glassforming material CKN (calcium potassium nitrate) revealed spectral structure and scaling properties strikingly similar to the predictions of the mode coupling theory of the liquid glass transition developed by Wolfgang Gotze and his coworkers. Initial correspondence and discussions in 1991 began a collaboration which has grown steadily and has been immensely satisfying and productive. Wolfgang Gotze and his coworkers have constructed the first coherent dynamical theory of supercooled liquids and the glass transition, and he has been exceptionally helpful in working with experimentalists to make critical tests of the theory through detailed data analysis. I have learned much physics from our discussions and have come to deeply prize the friendship and warmth that has characterized our collaboration. Wolfgang and his students have given generously of their time and effort, and this generosity is deeply appreciated. Much work remains to be done. Wolfgang and his group have worked steadily to complete the theory and extend its range of validity; new experiments are needed to test their predictions in detail. I hope to continue to participate in this effort and look forward enthusiastically to our continued collaboration Anyone entering the field of glass transition research will be immediately confronted by a large and frequently contradictory literature spanning over 100 years. Many theoretical papers have appeared, each claiming to “explain” the liquid-glass transition. These theories often contain unstated approximations or imprecisely defined quantities (e.g., the free volume), and their assumptions are usually incompatible with those of other competing theories. Experimental papers (with some exceptions) usually present a limited set of data which is compared with a single favored theory, bypassing the effort required to carry out detailed comparisons with different theories. There is clearly a serious need to begin intercomparing the many competing current theories. We have recently begun to carry out a critical review of existing theories of the liquid-glass transition and the structure and dynamics of the glassy state. Our plan is to use a variety of experimental data, primarily dynamical data obtained from spectroscopic studies of various glasses and supercooled liquids, to carry out comparative fits to various theories. The goal of this program is to determine if one (or more) of the currently available theories, or some combination of these theories, can provide satisfactory descriptions of a range of different experimental data; concurrently, we will try to see if some theories can be definitely shown to be inapplicable on this basis. This is a large program which is still in its early stages. What follows, therefore, is a preliminary report that should be viewed as “work in progress” to be extended as the analysis proceeds.