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Enhanced Mass Selectivity in Thermal Field-Flow Fractionation Due to the Temperature Dependence of the Transport Coefficients
Separation Science and Technology (1996)
  • Gwon-Hee Ko, Boise State University
  • Robyn Richards, Boise State University
  • Martin Schimpf, Boise State University
Abstract
Mass selectivity in thermal field-flow fractionation (ThFFF) is governed by the dependence of molecular weight M on the ratio of the diffusion coefficient D to the thermal diffusion coefficient D T. Although studies indicate that D T is independent of molecular weight in homopolymers (meaning that mass selectivity depends on differences in D alone), the greatest possible dependence of D on M predicted by polymer theory is not enough to account for the selectivity obtained in certain polymer-solvent systems. However, the increased selectivity can be explained by the temperature dependence of D/D T. Thus, lower molecular weight polymers, which are less compressed against the cold wall, experience a higher mean temperature. Since values of D/DT increase with temperature, the decrease in retention with M is greater than that predicted without considering the temperature dependence. We quantify the increased selectivity for polystyrene in ethylbenzene using a temperature-dependent value of D/D T in the concentration profile. When the temperature dependence of D/D T is removed, the selectivity decreases from 0.646 to 0.574. Although it does not constitute proof, the lower value is consistent with D T being independent of
Disciplines
Publication Date
July 1, 1996
Citation Information
Gwon-Hee Ko, Robyn Richards and Martin Schimpf. "Enhanced Mass Selectivity in Thermal Field-Flow Fractionation Due to the Temperature Dependence of the Transport Coefficients" Separation Science and Technology Vol. 31 Iss. 8 (1996)
Available at: http://works.bepress.com/martin_schimpf/42/