SEPARATION OF PARTICLES IN NONAQUEOUS SUSPENSIONS BY THERMAL FIELD-FLOW FRACTIONATION

The ability of thermal held-flow fractionation (ThFFF) to retain and separate both submicrometer and micrometer size particles (latexes and silica) suspended in various organic carrier liquids is demonstrated, The dependence of particle retention on various factors is evaluated and discussed. These factors include solvent properties, amount of added electrolyte, particle size and composition, and cold-wall temperature. Evidence of retention perturbations due to electrostatic particle-wall interactions is provided, and the efficacy of modifying the ionic strength of the organic carriers (by adding salt) to minimize the perturbations is demonstrated, General similarities and differences in retention behavior of particles suspended in nonaqueous as opposed to aqueous carriers are determined, One notable difference is the decrease in particle retention time in nonaqueous liquids with increasing cold-wad temperature; this trend is the same as that exhibited by polymers dissolved in organic carriers but is opposite to that shown by particles suspended in an aqueous medium. Thermal diffusion coefficients of several latex/solvent combinations are obtained from the ThFFF retention data. The present studies are limited primarily to polar organic solvents, except for some measurements involving cyclohexane and aqueous carriers, The investigation of nonpolar organic suspension media was hampered by either the solubility of the latexes or immiscibility between the original suspension media of the latexes and the nonpolar organic solvents.