(450c) Generalized Phase Diagram And Metastable States Of Molecular Solutions

Prediction and understanding of the thermodynamic properties and kinetics of phase transitions in molecular solutions depends on characterization of intermolecular interactions. As a probe of solute pair interactions we use the long-time self diffusivity determined by pulsed-field gradient nuclear magnetic resonance. The pair contribution of the scaled long-time self diffusivity D2 is used as a measure for the strength of solute interactions and aids in the development of a generalized phase diagram.

A corresponding-states behavior of solubility for a variety of molecules is demonstrated, suggesting that advances made in understanding the equilibrium phase behavior and kinetic phase transitions using simple fluid theories can be applied to a wide variety of molecular and colloidal systems. Metastable states occur when systems are trapped in local free energy minima for sufficiently long periods of time that they can be observed. Some practical uses of these states include glasses and gels. Often these states are achieved with colloidal particles and can be seen in such diverse places as toothpaste, hand cream, paints and car tires. Two metastable states are of interest here. The first are liquid states that are achieved by quenching a suspension rapidly below its solubility point, which are often reported in protein and nanoparticle suspensions. The second state is that of gels ? space filling networks where the particles display extremely sluggish self diffusion. These states are commonly seen in colloidal suspensions and reported with less frequency in molecular solutions. Here we explore the existence of these states in molecular solutions.