| This dissertation is an investigation of the effects of strong, directional bonds upon the thermodynamics and dynamics of network forming fluids. It comprises two related components. The first addresses the thermodynamic and dynamic implications of hydrogen-bonded networks in water and sugar-water solutions. The second focuses on the development and solution of a statistical mechanical model of inverse melting, a process in which a crystal isobarically melts into fluid upon cooling (a phenomenon of relevance to the stability of proteins in water under pressure).; The effects of strong directional bonds upon the interfacial properties of supercooled water are studied analytically utilizing two microscopic models of water, the van der Waals theory of inhomogeneous fluids, and two approximations for the influence coefficient. The predictions yield insights into the interfacial properties of supercooled water, including water's conjectured liquid-liquid transition. A theoretical framework for studying the solid-fluid equilibrium of water is also introduced. Four phases were considered: two low-density solid phases, one high-density solid phase, and the fluid phase. General water-like freezing behavior is predicted, including two triple points.; To explore the effects of hydrogen bonds on the dynamics of binary sugar-water solutions, quasi-elastic neutron scattering experiments were performed. Trehalose-water and fructose-water solutions were studied over a range of temperatures and sugar concentrations. The results show appreciable changes in the dynamics of these solutions as the sugar concentration and temperature are varied. Results suggest that both fructose and trehalose affect the long-time dynamics of water but that only the former, in addition, affects the short-time dynamics of water.; Finally, a statistical mechanical model for inverse melting, a phenomenon in which a crystal melts upon isobaric cooling, is proposed and investigated. Our theory is an idealized statistical mechanical representation of a polyatomic species with internal degrees of freedom whose intermolecular interactions are Gaussian. By a suitable choice of parameters the resulting equation of state predicts inverse melting that is accompanied by either negative or positive volumes of melting. |
