(485b) iCVD Modified Electrospun Membranes for Membrane Distillation

The rising demand for clean water has intensified the necessity for large scale seawater desalination processes. Membrane Distillation (MD) is one method for desalination, which relies on a temperature gradient to allow for water vapor to diffuse through a membrane. While MD is useful for treating highly concentrated feed solutions, the challenge comes with finding an appropriate membrane. Membranes fabricated through electrospinning exhibit many important characteristics for MD including high porosity and low tortuosity. These fibers must also exhibit hydrophobicity to prevent wetting. Many of the most spinnable and strongest polymer fibers are derived from hydrophilic fibers, making their use in MD challenging. Using the most spinnable polymer and then modifying the membrane for hydrophobicity would enable all polymers to be considered for this new type of membrane.

This work investigates the use of initiated chemical vapor deposition (iCVD) as a fiber modification technique for electrospun membranes. PAN and PVDF nanofiber membranes were fabricated using electrospinning to produce flat sheets. The fibers were then coated with a hydrophobic polymer, divinylbenzene (DVB), through iCVD. Since iCVD is a vapor phase, conformal coating technique, depositing a hydrophobic polymer onto the fiber mat can render any polymer fiber hydrophobic and viable for MD. The deposition rate for the iCVD coating was also investigated with the goal of accelerating the coating process. The membrane coupons were tested in a bench top direct contact membrane distillation unit with highly concentrated sodium chloride as the feed solution. It was discovered that the nanofiber membranes exhibited higher flux than commercial PVDF membranes, which can be attributed to the improved properties of the membranes through electrospinning and the conformal hydrophobic coating.