• Starts: 2:00 pm on Tuesday, November 29, 2022
  • Ends: 3:30 pm on Tuesday, November 29, 2022
Fluid polyamorphism is the existence of different condensed amorphous states in a single-component fluid. It is either found or predicted, usually at extreme conditions, for a broad group of very different substances, including helium, carbon, silicon, phosphorous, sulfur, tellurium, cerium, hydrogen, and tin tetraiodide. This phenomenon is also hypothesized for metastable and deeply supercooled water, presumably located a few degrees below the experimental limit of homogeneous ice formation. In this dissertation, I firstly discuss a fluid composed of two molecular species that may undergo phase segregation or phase amplification when two molecular species may interconvert. Secondly, I investigate the emergence of dissipated structures in mixtures with molecular interconversion in the presence of a source. Next, I compare a modified Cahn-Hilliard-Cook theory for spinodal decomposition in a binary mixture that exhibits both diffusion and interconversion dynamics and obtain a qualitative agreement with simulations of the temporal evolution of the order parameter and structure factor in a nonequilibrium Ising/lattice-gas hybrid model in the presence of an external source of forceful interconversion. Lastly, motivated by recent discoveries of the liquid-liquid phase transition in sulfur and hydrogen, I propose a simple model to describe liquid polyamorphism in a variety of chemically reacting fluids. The model combines the ideas of two-state thermodynamics with the maximum-valence approach, in which atoms may form covalent bonds via a reversible reaction, changing their state according to their bond number. By mimicking the valence structure and maximum bond number, z, my model predicts the liquid-liquid phase transition in systems with dimerization (z = 1), polymerization (z = 2), and gelation (z > 2). In particular, I show that when the bonded atoms repel or attract each other stronger than the unbonded atoms, phase separation is coupled to polymerization generating the liquid-liquid phase transition in polyamorphic substances.
PRB 595
Nikolay Shumovskyi
Nikolay Shumovskyi
Boston University, Department of Physics