Derek G. Leaist Professor B.Sc. Queen's Ph.D. Yale Office: Rm 067, Lab Rm 053 Chemistry Building Office: 661-2111, ext 86317
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Thermodynamic and Transport Properties of Solutions
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Awards:
• Bucke Award
• Lash Miller Award
• Award for Excellence in Undergraduate Teaching
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Current Research Programs:
Most of our research involves studies of diffusion - the transport of matter by random thermal motions. Experimental results for well characterized systems are used to test current ideas about diffusion and to develop new ones. Special emphasis is placed on multicomponent systems, coupled diffusion, and the interrelation of thermodynamic and transport properties
Systems of current interest include mixed electrolytes, micelles, microemulsions, polymers, and associating solutes. Our studies of these systems are motivated by basic scientific curiosity and by the immense practical importance of diffusion in processes such as crystallization, dissolution, mixing, gas absorption, electrode reactions, membrane transport, and corrosion.
Despite the vast number of multicomponent solutions of practical significance, relatively little is known about their diffusion properties. Diffusion in these systems is "coupled". In fact, substances can diffuse "uphill", from lower to higher concentrations, opposite to the expected direction. In recent years we have developed liquid-chromatography peak-broadening techniques for the rapid and convenient measurement of this kind of diffusion.
Our work has shown, for example, that protein concentration gradients co-transport hundreds or even thousands of moles of salt and buffer electrolytes for each mole of diffusing protein. In another study, coupled diffusion was shown to play a major role in the chemical scrubbing of acid gas pollutants by alkanolamine absorbents.
To interpret the experimental results, we run numerical simulations and use Nernst-Planck and related theories of diffusion. In mixed electrolyte solutions, for example, the coupled flow of each electrolyte can be resolved into contributions from: 1) pure-diffusion of ions down concentration gradients; and 2) the migration of ions in the electric field generated by the diffusion of ions of different mobilities
Another topic of interest is coupled diffusion of driven by temperature gradients (thermal diffusion), a process of growing importance in the separation and characterization of polymers and colloids. Building on our experience with peak-broadening techniques, flow cells are being designed and tested for the rapid and convenient measurement of thermal diffusion.
Selected Publications:
Kelly, B. and Leaist, D. G. Using Taylor Dispersion Profiles to Characterize Polymer Molecular Weight Distributions. Phys. Chem. Chem. Phys. 6, 5523-5530 (2004).
Halvorsen, H. and Leaist, D. G. An Electrostatic Mechanism for the Coupled Diffusion of Polymer Molecules and Ionic Micelles. Aqueous Poly(ethylene glycol) + Sodium Dodecyl Sulfate Solutions. Phys. Chem. Chem. Phys. 6, 3515-3523 (2004).
Pellumb, J. Halvorsen, H. and Leaist, D. G. A Thermodynamic Interpretation for the "Excluded-Volume" Effect in Coupled Diffusion. J. Phys. Chem. B. 108, 7978 -7985 (2004).
MacEwan, K. and Leaist, D. G. Quaternary Mutual Diffusion Coefficients for Aqueous Solutions of a Cationic-Anionic Mixed Surfactant from Moments Analysis of Taylor Dispersion Profiles. Phys. Chem. Chem. Phys. 5, 3951-3958 (2003).
Chan, J., Popov, J. J., Kolisnek-Kehl, S. and Leaist, D. G. Soret Coefficients for Aqueous Poly(ethyleneglycol) and Some Tests of the Segmental Model of Thermal Diffusion. J. Solution Chem. 32, 197-214 (2003).
