Molecular Thermodynamics for Phase Equilibria in Mixtures:

Introduction

The goal of our research is to increase fundamental understanding of the equilibrium properties of solutions; we need this understanding not only for scientific purposes but also for providing the basic information required in chemical-process and chemical-product design. We are particularly concerned with (1) properties of aqueous multi-protein solutions, to induce or prevent aggregation or precipitation; (2) properties of polymer solutions, especially those containing block copolymers or gels for design of contact lenses and drug-delivery devices; (3) properties of ionic liquids with application to batteries, separation processes and for media to promote synthesis of selective chemical and biochemical products.

Our research consists of carefully selected experimental studies coupled with molecular simulations and theoretical efforts to interpret and correlate physico-chemical data for engineering-oriented applications.

 

Research Abstracts

We focus on three areas.

1. Molecular Thermodynamics of Aqueous Protein Precipitation (with Professor Blanch)

Primary Project Goal: To establish a rational design procedure for a large-scale process to separate aqueous protein mixtures by selective precipitation using one (or more) salts; and to study fibril formation, a probable cause of Alzheimer’s disease.

In our studies, we use concepts from colloid theory; the primary requirement is a reliable potential of mean force. To establish that, we measure osmotic pressures, dynamic laser-light scattering and low-angle laser-light scattering for protein solutions under a variety of conditions (primarily pH, ionic strength and additives such as alcohols). The potential of mean force is introduced into an expression for the Helmholtz energy obtained from the integral theory of fluids. From this expression we obtain chemical potentials and thus we can establish the phase diagram for fluid-fluid and fluid-solid equilibria. – We use chromatography and light scattering to determine how fibril information can be suppressed with biochemical chaperones.

We also do extensive molecular simulations toward establishing the conditions when amino-acid chains will fold to form biologically active proteins or misfold to form precipitating aggregates.

II. Phase Equilibria and Transport in Polymer Solutions (with Professor Radke)

Primary Project Goal: To determine and correlate thermodynamic properties (phase equilibria) for systems containing solvents and polymers, especially block copolymers and gels.

Polymers are used for manufacturing numerous products including packaging materials, drug-delivery devices and contact lenses. Process and product design often require quantitative information on phase equilibria and diffusivities for solvent-polymer systems. For example, design of next-generation contact lenses requires water-gel equilibria, while design of new transdermal drug-delivery systems (patches) requires solubilities of drugs in polymeric films. Toward establishing phase equilibria and diffusivities for such (and similar) applications, experimental, theoretical and molecular-simulation research is in progress.

 

III. Properties of Ionic Liquids for Chemical Engineering Applications (with Professor Newman)

Despite much progress in recent years, little is known about the properties of ionic liquids; an ionic liquid is a molten salt whose melting temperature is near (or below) 25 °C. Such liquids are of interest as “green” solvents because, at ordinary temperatures, they have essentially zero vapor pressure. They tend to be chemically stable and nontoxic. Ionic liquids may be useful for separation operations such as sweetening of sour natural gases (by absorption of CO2 and H2S) or as extraction solvents for removal of dangerous heavy-metal ions (e.g. Hg, Sr, Zn, Cd) from aqueous solutions. Ionic fluids show much promise as electrolyte media in batteries, fuel cells and other electrochemical devices. Our research concerns characterization of lithium salts in ionic liquid properties based on UV and NMR spectroscopy and cyclic voltammetry; determination of electrochemical properties (e.g. conductivity) of ionic liquids in lithium batteries; measuring and correlating distribution coefficients of ions between water and an ionic liquid using plasma spectroscopy; and development of a statistical-mechanical theory for correlating solubilities of gases and activity coefficients of organic solvents in ionic liquids; establishing criteria for selecting the optimum ionic liquid as a medium for a desired chemical or biochemical reaction.

 

Group Members
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