SEPARATION OF PARTICLES IN AQUEOUS SUSPENSIONS BY THERMAL FIELD-FLOW FRACTIONATION - MEASUREMENT OF THERMAL-DIFFUSION COEFFICIENTS

Thermal field-flow fractionation, which for over two decades has been focused on the separation and characterization of polymers in nonaqueous solutions, is shown here to be capable of separating various latex and silica particles in aqueous suspensions. Both submicron (down to 30 nm diameter) and micron sized particles are separable by normal and steric modes of thermal FFF, respectively. The selectivity is intermediate between that of sedimentation FFF and flow FFF. For normal mode operation, resolution, speed, and size range are flexibly controlled by adjustments in the field strength and flowrate. The thermal diffusion phenomenon underlying separation is investigated and thermal diffusion coefficients are obtained from the thermal FFF data. Thermal diffusivity differs somewhat among different types of latex particles but is stronger for all latexes than for silica particles. The implications for compositional as well as size analysis are discussed. The behavior of particles and polymers in a strong temperature gradient are compared and shown to differ in several significant respects.