COLLABORATION IN BASIC SCIENCE AND ENGINEERING (COBASE)

Dr. Martin Schimpf hosted Dr. Semen Semenov at the Boise State University Department of Chemistry on a COBASE long-term grant from August 1999 to February 2000. Dr. Semenov is a professor at the Biophysics Institute of the Russian Academy of Sciences. Drs. Schimpf and Semenov began their collaboration with detailed discussions on the topic of thermophoresis. This complex phenomenon, which is used to separate a wide range of materials from oil fractions to polymer mixtures, is poorly understood. The collaborators hoped to combine Dr. Schimpf's understanding of thermophoresis based on several years of empirical study with Dr. Semenov's experience in modeling transport phenomena.

From discussions on polymers and trends in their thermophoresis behavior, the collaborators were able to outline a general mechanism of polymer thermophoresis in nonpolar solvents that they believed to be consistent with laboratory observations. By using the general dependence of interaction potentials on the distance between interacting objects, Dr. Semenov produced an elegant expression that relates polymer thermophoresis to parameters that can be independently measured. Values of the thermophoretic mobilities calculated from the model follow the same general trends as those measured in the laboratory. For example, the model correctly predicts the stronger thermophoresis of polymethylmethacrylate. It is also consistent with the observation that thermophoresis is weak in water compared to less polar solvents.

The polymer model was recently published in the Journal of Physical Chemistry. It was also presented at the Fourth International Symposium on Thermodiffusion in Bayreuth, Germany, September 2000. This presentation is expected to lead to further collaborations. Drs. Schimpf and Semenov are also discussing the feasibility of incorporating the model into computer-aided molecular dynamics calculations.

During the final three months of the collaboration, the researchers turned their attention to developing a model for the thermophoresis of latex emulsions in polar liquids. This model was tested using measurements of thermophoresis on latex particles by thermal field-flow fractionation (thermal FFF). Consistent with prediction of the model, thermophoresis of polystyrene latex particles in different buffers approaches the same value in the limit of diminishing particle size. This model was also recently accepted for publication to the Journal of Physical Chemistry.

A grant proposal has been submitted to the National Science Foundation. This proposal focuses on additional theoretical and experimental studies of thermophoresis in polymer solutions and particle suspensions. In a separate proposal, Drs. Schimpf and Semenov aim to study the potential of combining electrophoresis and thermophoresis in the development of more efficient separation and measurement tools, with a particular focus on miniaturized devices that incorporate waveguide technology.