Supermolecular structure formation of PMP membranes: Theoretical argumentation in terms of the experimental evidences

Experimental and model research lines related to the formation of the polymeric membranes cast from solutions, and associated with their morphologies, are presented. In order to determine the formation's main characteristics, the mechanism governing the polymer crystallisation and/or lamellae aggregation is proposed. It is based on a theoretical Smoluchowski-type argumentation. Poly(4-methyl-1-pentene) has been used as a material for the study. Morphology of the lamellae-containing membrane materials is discussed. Two main topics are addressed: a three-phase model (‘real’ and ‘ordered’ amorphous phases, and a crystal phase), and factors affecting the supermolecular structure of the membranes. Special attention is paid to lamellae perfection in the solution of different polymer concentrations and its relation to the thin-film type morphology. The stages of the crystallisation are proposed mainly in terms of the role played by the solvent molecules. The optimal circumstance for the formation of the polymeric membranes with the highest degree of crystallinity is indicated. This optimal circumstance points to consider thoroughly the polymeric membrane formation as a thermodynamic–kinetic process of diffusive nature. As a consequence, the process manifests ultimately in a stationary state of the nucleation-growth and ripening-involving viscoelastic phase transformation. Moreover, it is complemented by explicit involvement of two most relevant interaction contributions, i.e. polymer–solvent and polymer–polymer, typically prevailing in a concentrated binary mixture, with the solvent–solvent interaction in a background. As a result of the experimental data analysis, performed in the frames of the proposed theoretical model, a fitting function is derived explicitly and applied to the crystallinity–concentration relationship.