Latex particle thermophoresis in polar solvents

A theoretical model is presented of the thermophoresis of latex particles i n polar solvents. Expressions for the thermophoretic mobility (TM) of the p articles, which consist of polymer solutions emulsified in a poor solvent w ith the addition of salt, are obtained. The model is based on the thermopho resis of polymer chains partitioned between the emulsion droplet and the su rrounding solvent. The partitioning is assumed to originate with the "salti ng in" of monomer units (mers) in the surfactant film that surrounds and st abilizes the latex particle. Correlation between mers then leads to a parti tioning of mers between the good solvent inside the latex particle and the surrounding poor solvent. Assuming a mer concentration th;tt decays exponen tially into the surrounding solvent, the expression for the particle TM is obtained. It is found that, with the increase of the square of the derived dimensionless parameter, the latex particle TM increases from zero to a hyp othetical value of the polymer's TM in the poor solvent. The dimensionless parameter contains the product of mer concentration at the particle surface , the mer radius, and the square of the mean thickness of the mer distribut ion in the external solvent. Based on experimental data, the dimensionless parameter has a value greater than or equal to unity for polystyrene in the polar solvents water and acetonitrile. The TM of polystyrene in these syst ems is comparable with that of polystyrene in nonpolar solvents.