LIQUID-LIQUID IMMISCIBILITY IN SINGLE-COMPONENT NETWORK-FORMING FLUIDS - MODEL-CALCULATIONS AND IMPLICATIONS FOR POLYAMORPHISM IN WATER

Analytical calculations and Monte Carlo simulations of a lattice model of a tetravalent network-forming fluid show liquid-liquid immiscibili ty at low temperatures. Three types of phase behavior are found to occ ur: Vapor-liquid equilibrium, vapor-liquid equilibrium plus liquid-liq uid immiscibility with an upper critical temperature, and vapor-liquid equilibrium plus closed-loop liquid-liquid immiscibility. The coexist ing liquids differ appreciably in density, structure, and molecular dy namics. The low-density liquid displays more structured, open networks , and slower translational and network-restructuring dynamics than the high-density Liquid. The model provides useful insights into the mole cular basis of low-temperature immiscibility in network-forming fluids , and its relation to the unusual transition between distinct amorphou s phases in vitreous water.