Abstract:Spin-coating technique applied to film preparation stands out among other techniques owing to its advantages in terms of affording precise control of film thickness and producing minimal pollution in addition to being cost effective and energy saving. In this study, a PVDF/PTFE composite membrane was prepared by spin-coating; the preparation process was optimized, and the mechanism of film formation in spin-coating was investigated. Through single-factor experiments, the effects of the concretion of PVDF solution, spin speed of the spin coater, and the film-forming temperature on the tensile strength and water flux of the composite membrane were examined. The variations in pore size of the composite film adhesive layer were analyzed using scanning electron microscopy. The results showed that the optimum preparation conditions for PVDF/PTFE composite membrane were as follows: PVDF solution concentration of 6 g/L; coater spin speed of 2500 r/min, and film-forming temperature of 90 ℃. Under these conditions, the film thickness of the prepared composite film was 200 μm, the average pore size was 20 μm, the tensile strength reached up to 26.34 MPa, and its water flux reached up to 605.2 L/(m2·h). Furthermore, the mechanism of PVDF/PTFE composite film formation using spin-coating involved Van der Waals forces and other intermolecular forces acting between PVDF sol molecules and the PTFE micro-porous membrane, while the adhesive effects resulted from hook bonding and nail bonding formed by penetration of PVDF sol-gel molecules into the pores of the PTFE membrane.
