Fundamental Studies of Metastable Liquids

Research Objectives

The broad theme of my research project addresses fundamental problems in metastable liquids and glasses. Metastable liquids are ubiquitous in nature (clouds, living systems surviving under sub-freezing conditions, fluid transport in plants) and in technology (cavitation erosion; vapor explosions; cryopreservation of cells, seeds, and labile biochemicals in supercooled emulsions; pharmaceutical formulations). However, the connection of metastable liquids to the rigorous molecular theory of matter remains incomplete. My research aims at enriching fundamental understanding of metastability.

Computational Approach

In our work we use computational methods we have previously developed for simulating fluids under constraints (restricted ensemble), which we then use to explore the relationship between fluid properties and the severity of the applied constraint. Additionally, we have examined the topology of the multi-body potential energy surface in supercooled liquids via the corresponding inherent structures or local potential energy minima. This requires large-scale minimizations for systems having on the order of 10³ degrees of freedom.

Accomplishments

A representative example of the progress we have made during the past year is that by the approach described above, we have been able to demonstrate that the onset of nonexponential relaxation and of non-Arrhenius dependence of the structural relaxation time correspond to a well-defined temperature, below which the depth of the potential energy minima explored by the liquid decreases with temperature, and above which it does not.

We have also found that the energy landscape approach provides valuable insight into the mechanical stability of liquids and its possible relevance to the process of vitrification.

Significance

Our findings suggest a general way of describing supercooled liquids. A long-term application would be to use this approach to predict for any fluid the temperature dependence of its low-temperature properties, based only on the microscopic interactions between the molecules.

Additionally, many of the techniques we employ and develop have applications that are not restricted to metastable states. Hence, our research has broad implications for the understanding of the liquid state of matter in general.

Publications

P. G. Debenedetti, D. S. Corti, S. Sastry, and F. H. Stillinger, "Constraints, metastability, and inherent structures in liquids," Phys. Rev. E 55, 5522 (1997).

P. G. Debenedetti, S. Sastry, and F. H. Stillinger, "Statistical geometry of particle packings: II. Weak spots in liquids," Phys. Rev. E 56, 5533 (1997).

------, "Signatures of distinct dynamical regimes in the energy landscape of a glass-forming liquid," Nature 393, 554 (1998).

http://www.princeton.edu/~pdebene