Polyvinylidene fluoride (PVDF) thin films are highly non-reactive and hydrophobic, making them ideal for application in many membrane-based processes such as protein analysis and water purification. Currently, electrospinning is one of the most common techniques for manufacturing PVDF films. The present work investigates the effect of cyclic spin coating techniques on the properties of isoporous PVDF micro-membrane films. The films were prepared by dropping PVDF cast solution onto a mold with a uniform 120mm x 120mm square pore pattern and spinning the mold on a spin coater. Three patterns of spin coating cycles were investigated: (1) 3 consecutive 90-s cycles,  with each cycle consisting of acceleration from 0-100 rpm for 15 seconds, hold for 60 seconds, and deceleration to 0 rpm for 15 seconds; (2) 3 consecutive 60-s cycles, with each cycle consisting of acceleration from 0-200 rpm for 15 seconds, hold for 30 seconds, and deceleration to 0 rpm for 15 seconds; and (3) 7 consecutive 60-s cycles, with each cycle similar to pattern (2). An analysis of the physical and chemical properties of the membranes (tensile strength, hydrophobicity, flux) shows superior membrane properties for membranes spun at higher speeds and longer cycles (Pattern 3). At lower speeds, the PVDF solution did not sufficiently spread on the mold, causing uneven film thickness and leaving higher amounts of residue when the film was transferred from the mold. In contrast, the PVDF solution spread more evenly into the mold when spun at higher speeds. It is hypothesized that by employing alternating fast and slow speed spin coating cycles, the higher deposition speeds within each cycle produced more dispersed films, while the slower speeds allowed the solution to more homogeneously fill into the mold channels. The results of this study indicate the potential for improving PVDF membrane properties by doing a simple modification to traditional spin-coating techniques in membrane manufacture.

Manufacture of PVDF film membrane using soft lithography: Effect of spin coating

256th National Meeting (2018)

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