Thermophoresis of a polyelectrolyte*

Thermophoresis, the migration of a species due to a temperature gradient, has been shown to be a possible mechanism for manipulating molecules in microfluidic devices. The mechanism governing thermophoresis is complex making a molecule's Soret coefficient (S$_{T})$ and its dependence on different physical factors hard to predict. We experimentally investigate thermophoresis of a polyelectrolyte. For sufficiently high average temperatures, two forms of the molecule are present. We measure the Soret coefficient of both and find that one has positive S$_{T}$ and the other negative. We also investigate the dependence of S$_{T}$ on co-dissolved ionic species, specifically NaOH and NaCl.