On the effect of thermophoretic force, gravitational force, and particle–particle interactions in field-flow fractionation

Abstract

ABSTRACTThe theoretical calculations confirmed that the gravitational force cannot be neglected in all field-flow fractionation techniques separating nanometer-sized colloidal particles whenever particle diameter is approximately 200 nm and larger. Particle–particle repulsive interactions, mostly electrostatic repulsions, influence substantially concentration distribution established by any effective field acting across the fractionation channel, as confirmed explicitly for thermophoretic force generated by temperature gradient in microthermal field-flow fractionation. The ionic strength of the carrier liquid causes the screening of the electrostatic double layer around the dispersed particles and thus influences the retention. The attractive particle–particle forces occur when the zeta potential of the particles approaches to 0 mV, the electrostatic repulsions are screened, and the aggregation of the particles is observed. The pH influences differently the size and zeta potential of the plain polystyrene latex particles and of the particles modified on the surface by the groups –COOH and –NH2. The role of a detergent in carrier liquid is non-negligible, as demonstrated by its presence or absence in carrier liquid.