Focusing Mechanisms in Micro-thermal Field-Flow Fractionation

Progress in theory of separation mechanisms controlling the Micro-Thermal Field-Flow Fractionation of the macromolecular and particulate species inspired the development of the experimental methodology and instrumental techniques. Three really functioning separation mechanisms are polarization, steric and focusing. However, steric mechanism is rather exceptionally operative for the separation of large particles at low flow rates of the carrier liquid. On the other hand, two modus operandi taking advantage of focusing mechanism emerging at high flow rates and, consequently, resulting in very rapid separations are elaborated. One exploits the action of the lift force and the other one makes use of the kinetic energy generated by the collisions among the particles in bi-disperse suspension of the particulate species. Surface properties and their topographical heterogeneity influence the migration of particulate species exposed to the force of thermal diffusion. The shape of the spherical versus non-spherical particles distinguishes their behavior when exposed to thermal diffusion and to hydrodynamic stress. It was theoretically calculated that the separations of the particles, based on the mentioned differences, are possible by Focusing Micro-Thermal Field-Flow Fractionation. Since our earlier theoretical models were not developed in sufficient details, some of the previous results are corrected by the present paper. The theoretical conclusions are supported by preceding real separations.