Compressibility and crystalline structures of PVDF membranes under elevated gravity acceleration by two-axis spin coating technology

Abstract

Polymers play an important role in designing and manufacturing lithium–ion batteries and sensors. This study investigates the compressibility and crystalline structure of polyvinylidene fluoride (PVDF) membranes spin-coated under different gravity conditions. Particle Flow Code (PFC) numerically models the compressibility of membranes. The models show a 10% reduction in the thickness of the membrane when the gravity is artificially elevated to 500g. The time of solvents’ release from the free surface of membranes based on Stokes’ law is simulated by MATLAB. The results show that the solvents’ release time decreases significantly when the artificial gravity increases. Novel experiments are conducted to validate the results of numerical modeling and MATLAB simulations. Four PVDF membranes are spin-coated by a novel two-axis spin coater under 1, 100, 300, and 500g. The SEM images experimentally report a 21% reduction in the thickness of the membrane spin-coated under 500g. The weights of membranes are measured to verify the results of MATLAB simulations. The results show that 99% of the whole solvents are evaporated while increasing the gravity to noticeable values. XRD, FTIR, and SEM characterize the polymeric crystalline structure of membranes. The crystalline structure of spin-coated PVDF membranes varies under various gravity conditions. The XRD measurements report phase transitions, while the gravity is artificially elevated during membranes’ fabrication. FTIR spectroscopy revealed that the observed phase transition is from γ toward β while increasing the gravity acceleration.