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Location

Disque Hall, Room 919, 32 South 32nd Street, Philadelphia, PA 19104

Audience

  • Undergraduate Students
  • Graduate Students
  • Faculty

Physics Colloquium: Glass Polymorphism in Water and Aqueous Solutions

Thursday, May 21, 2015

3:30 PM-4:30 PM

Nicolas Giovambattista, PhD, CUNY, Brooklyn

 

Most liquids form a single glass or amorphous solid state upon rapid cooling. However, there are a few substances, relevant to scientific and technological applications, that can exist in at least two different amorphous solid states, a property known as glass polymorphism. Examples include silicon, silica, and in particular, water. In the case of water, experiments show the existence of a low-density (LDA) and high-density (HDA) amorphous ice that are separated by a dramatic, first-order like phase transition. In the first part of this talk, I will present results from extensive out-of-equilibrium molecular dynamics simulations of glassy water where we study (i) pressure- and (ii) heating-induced transformations between LDA and HDA. Our results show that MD simulations of simple water models can indeed reproduce the phenomenology associated to the LDA-HDA transformations. For example, simulations reproduce the sharp, large density changes (>20%) that characterize the LDA-HDA transformations. Tracing the LDA-to-HDA and HDA-to-LDA transformation temperatures in the P-T plane allows us to construct a "phase diagram" which is also consistent with experiments. One of the open questions in glassy water is what the glass transitions of LDA and HDA [Tg,LDA(P) and Tg,HDA(P)] are and in particular, how they vary with pressure. We address these questions by heating LDA and HDA at different pressures. Our simulations predict that Tg,LDA(P) is anomalous, i.e., it decreases with increasing pressure, while Tg,HDA(P) increases with increasing pressure. Surprisingly, we find that the glass transitions of LDA and HDA are related to the LDA-HDA transformations. In the last part of this talk, I will discuss the implications of water glass polymorphism to the behavior of glassy aqueous solution. I will present recent results from computer simulations on glassy water-glycerol mixtures at different concentrations and relate them with experimental data.

Contact Information

Prof. Brigita Urbanc
brigita@physics.drexel.edu