The Depletion/Adsorption Transition of Polymer Solutions in a Confined System

In the preparation of low density foam in small size systems like a capillary, the concentration distribution of polymer solution will affect the density uniformity of the foams. The behavior of a solution of ideal polymers at a wall surface was investigated using self-consistent field theory (SCFT). The depletion/adsorption transition of the solution concentration distribution in confined system will occur only in the case that the interactions among polymer segments, solvent and wall are changed. The conditions at the transition point were discussed, and the reciprocal of the polymer chain length and the difference of the interactive parameters of polymer segments and wall, solvent and wall, have good linear relationship at the transition point. In addition, the linear fitting constants are related with system dimension and bulk volume fraction of polymer solution when the system size is not large enough. In the case of polymer with polydisperse molecular weight, the smaller the molecular weight is, the closer the polymer chains approach to the wall. Higher polymer concentration, longer polymer chain, better solvents and smaller system dimension facilitate the occurrence of the depletion/adsorption transition.