Influence of bulk and surface composition on the retention of colloidal particles in thermal field-flow fractionation

Abstract

In this paper we report a wide range of cases in which the retention of colloidal particles in thermal field-flow fractionation (FFF) shows a strong dependence on the chemical composition of the particles or of the particle surfaces. These results are observed among similar particles (such as different latexes) or between dissimilar particles (including latexes as well as inorganic and metallic colloids). These compositional effects are observed for particles suspended in both aqueous and nonaqueous carrier liquids. The dependence of retention on composition is complementary to its dependence on particle size, which has been amply demonstrated in previous studies. The compositional effect is attributed to the dependence of the thermal diffusion coefficient on compositional factors. A number of cases are presented here where compositional effects are significant. Examples include the baseline resolution of 0.30-μm silica particles and 0.300-μm polystyrene (PS) particles and a large difference in retention times between 0.232-μm PS and 0.229-μm polymethylmethacrylate (PMMA) latexes in aqueous suspensions. Also, metallic particles (e.g., palladium) were less retained than silica particles, with latex particles most retained. The resolution of equal-size particles in the nonaqueous carrier liquid acetonitrile is also demonstrated. Surface compositional effects have also been found in this study. These effects suggest the possibility of colloidal surface analysis by thermal FFF. The potential for performing both bulk and surface compositional analysis of particles by thermal FFF makes this FFF technique complementary to both sedimentation FFF and flow FFF techniques for the analysis of complex particulate materials.