Polymer Analysis by Thermal-Diffusion Forced Rayleigh Scattering (CAT#: STEM-ST-0005-YJL)

Introduction

Thermal diffusion, also known as the Ludwig-Soret effect, is the occurrence of mass transport driven by a temperature gradient in a multicomponent system. Most data about the Ludwig-Soret effect of polymers in solution have been obtained from thermal field-flow fractionation (TFFF), developed by Giddings and coworkers. TFFF is one member of the family of field-flow fractionation techniques, which are all characterized by a laminar flow of the polymer solution or colloidal suspension within a relatively narrow channel. An external field, which may be gravitation, cross-flow, or temperature as in TFFF, is applied perpendicular to the flow channel and biases the concentration distribution. Fractionation in TFFF results from the competition between thermal and Fickian diffusion, which is molar-mass-dependent, and from the varying velocity of the solution at different distances from the channel wall.