Mechanism of PVDF Membrane Formation by NIPS Revisited: Effect of Precipitation Bath Nature and Polymer-Solvent Affinity.

A new interpretation of the mechanism of the polyvinylidene fluoride (PVDF) membrane formation using the nonsolvent-induced phase separation (NIPS) method based on an analysis of the complete experimental phase diagram for the three-component mixture PVDF-dimethyl acetamide (DMAc)-water is proposed. The effects of the precipitation bath's harshness and thermodynamic affinity of the polymer's solvent on the morphology, crystalline structure, transport and physical-mechanical properties of the membranes are investigated. These characteristics were studied via scanning electron microscopy, wide-angle X-ray scattering, liquid-liquid porosimetry and standard methods of physico-mechanical analysis.

Controlled Swelling of Monolithic Films as a Facile Approach to the Synthesis of UHMWPE Membranes.

A new method of fabricating porous membranes based on ultra-high molecular weight polyethylene (UHMWPE) by controlled swelling of the dense film was proposed and successfully utilized. The principle of this method is based on the swelling of non-porous UHMWPE film in organic solvent at elevated temperatures, followed by its cooling and further extraction of organic solvent, resulting in the formation of the porous membrane. In this work, we used commercial UHMWPE film (thickness 155 μm) and o-xylene as a solvent.

Analysis of the Thermal Behavior of Polypropylene-Camphor Mixtures for Understanding the Pathways to Polymeric Membranes via Thermally Induced Phase Separation.

An experimental phase diagram of the isotactic polypropylene-camphor system is constructed using an original optical method. It considerably deviates from the dynamic diagram, which can be obtained using conventional differential scanning calorimetry (DSC), and contains an additional boundary line that describes camphor solubility in the polymer. An accurate phase diagram makes it possible to perform a detailed and consistent thermodynamic analysis of the DSC, optical, and scanning electron microscopy data on the cooling of prehomogenized mixtures of different compositions, which leads to the formation of capillary-porous bodies via thermally induced phase separation.