Glass Transitions, Polyamorphic Transitions, and Chemical Order Freezing Transitions, in Liquids and Other Complex Systems

Arizona State University, Scottsdale AZ

Investigators

Abstract

This project aims to study glasses that are formed on extremely short time scales by "hyperquenching." Developed over decades to vitrify "bad" glassformers, hyperquenching has never been systematically applied to explore the high temperature structure and properties of common glassformers. The possibility of examining features of glassforming liquids in the absence of smearing by vibrational excitation is a central goal for this study. Some key results were obtained in the previous grant period supporting the concept of topological defects as elementary excitations in glasses, and experiments needed to properly develop this idea will be performed. Hyperquenching of glassformers like zink chloride (ZnCl2) containing site sensitive probes like cyanide ion CN- will be performed. Hyperquenching of complex ion containing glassformers will permit the definition of the second fictive temperature described in a recent paper. Initiated in 2004 are new glasses obtained by (i) "pressure-tuning" and (ii) mechanical damage. Pressure-quenched and damage-formed glasses will be examined as analogs of hyperquenched glasses. In addition, it is shown how, in systems with additional complexity over the usual glassformer, hyperquenching can open the door to detailed study of the complex process. This may be (i) a liquid-liquid phase change that can be quenched-in before it happens, and then studied at leisure during reheating, or (ii) a molecular structure change, such as the folding of a protein, or the progress of some chemical ordering process. In each case the preliminary proof of principle is given. using papers published during the present grant period. In this proposal some new points of departure for the experimental study of glassformers are outlined and resources to bring them to fruition are requested. Previous work in this group was focussed on liquids in metastable equilibrium, or on the transition from liquid to glass and back to liquid using similar time scales for cooling and heating. The new approach was originally designed to permit greater overlap with computer simulation, but has now been recognized as a strategy for exploring supercooled liquid states, and glassy state dynamics, in its own right. It is also motivated by the information on the nature of traps on the energy landscape (both their energetics and vibrational dynamics) that can be obtained by interrogation of the hyperquenched glass. %%% Under NSF support this author has just contributed an article on fundamental aspects of the glassy state to a book on Pharmaceuticals "Freeze Drying of Pharmaceuticals" because many of today's drugs are now being preserved in the glassy state by the freeze drying process. One of the reasons for this choice is that vitreous materials dissolve much more rapidly (in the stomach for instance) than do their crystalline analogs. This work on the thermodynamics and dynamic properties of glasses is of fundamental importance to the development of drug processing. This project on separating physical from chemical effects of hyperquenching will provide valuable training to both graduate and undergraduate researchers.