Effect Of Cacl2 Addition On Crystal Structure And Separation Performance Of Pvdf Membranes: An Experimental And Molecular Simulation Study

The inorganic salts addition can affect the interactions among the polymer chains and further influence the membrane structure. In this work, the effects of calcium chloride (CaCl2) on the crystal structure and separation performance of poly(vinylidene fluoride) (PVDF) membranes were studied. The influence of CaCl2 addition with varying concentrations (0-3 wt.%) was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and molecular dynamic (MD) simulations. XRD and FTIR characterizations indicated that CaCl2 could induce the transformation of PVDF crystal structure from a to p, which was further confirmed by molecular dynamic simulation. The MD simulation results revealed that the interaction between Ca2+ and F atom distorted the dihedral angle of PVDF chains, inducing the crystal structure transforming partially. SEM characterization indicated that the finger-like voids became longer and broader with increasing amount of CaCl2 addition. The membrane consisting of 0.7 wt.% CaCl2 exhibited the best performance with bovine serum solution rejection of 84.7% and water permeability of 203.6 L m(-2) h(-1 )bar(-1).