On the Concentration Effects in Micro-Thermal Field-Flow Fractionation of Polymers

Abstract

Micro-Thermal Field-Flow Fractionation (Micro-TFFF) was used to study the effect of concentration of the polymer solutions injected into the separation channel. The range of the investigated concentrations was very large, becoming higher then the critical values at which the entanglement of the polymer coils leads to the formation of the macromolecular aggregates. The samples of different molar masses were used and the experiments were carried out at different temperature drops across the channel and at different temperatures of the cold wall. The multiple peaks (or oscillations) that appeared on the fractograms at a given concentration of the injected sample solution and at a given temperature drop, disappeared at lower concentration and emerged again at the same lower concentration, but at a higher temperature drop. Although the observed broadening of the fractograms can be partially caused by the formation of the macromolecular aggregates, their presence cannot explain the secondary peaks or oscillations appearing on the fractograms at the retentions corresponding to extremely high molar masses. The hydrodynamic and/or gravitational instabilities, which are caused by the formed viscosity and density gradients inside the separation channel are the most probable explanation of the origin of the mentioned secondary peaks and/or oscillations emerging at high concentrations and/or high temperature drops.