Enhanced Mass Selectivity in Thermal Field-Flow Fractionation Due to the Temperature Dependence of the Transport Coefficients

Authors

Gwon-Hee Ko, Boise State University
Robyn Richards, Boise State University
Martin Schimpf, Boise State UniversityFollow

Document Type

Article

Publication Date

7-1-1996

DOI

http://dx.doi.org/10.1080/01496399608001332

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/D_T 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

Publication Information

Ko, Gwon-Hee; Richards, Robyn; and Schimpf, Martin. (1996). "Enhanced Mass Selectivity in Thermal Field-Flow Fractionation Due to the Temperature Dependence of the Transport Coefficients". Separation Science and Technology, 31(8), 1035-1044.