Abstract
Electrospun membranes have shown promise for use in membrane distillation (MD) as they exhibit exceptionally low vapor transport. Their high porosity coupled with the occasional large pore can make them prone to wetting. In this work, initiated chemical vapor deposition (iCVD) is used to modify for electrospun membranes with increased hydrophobicity of the fiber network. To demonstrate conformal coating, we demonstrate the approach on intrinsically hydrophilic electrospun fibers and render the fibers suitable for MD. We enable conformal coating using a unique coating procedure, which provides convective flow of deposited polymers during iCVD. This is made possible by using a 3D printed scaffold, which changed the orientation of the membrane during the coating process. The new coating orientation allows both sides as well as the interior of the membrane to be coated simultaneously and reduced the coating time by a factor of 10 compared to conventional CVD approaches. MD testing confirmed the hydrophobicity of the material as 100% salt rejections were obtained.
Highlights
Membrane distillation (MD) is a thermally driven desalination process that allows water vapor molecules to travel through a porous hydrophobic membrane [1]
Deposition occurred as the reactants diffuse to the bottom and adhere onto the exposed fibers
In order to achieve adequate hydrophobicity, the membrane must be coated on each side separately, which adds additional processing time as the chamber must be purged and brought back under vacuum again
Summary
Membrane distillation (MD) is a thermally driven desalination process that allows water vapor molecules to travel through a porous hydrophobic membrane [1]. Challenges remain in identifying appropriate membrane materials for MD as commercialization of the technology has stalled. MD membranes must be entirely hydrophobic to prevent any liquid penetration through the membrane while allowing vapor transport and preventing thermal transport. This means that these membranes must exhibit high porosity, low tortuosity, low thermal conductivity, and high mechanical and thermal stability [2]. The combination of these properties, some of which are counter to one another (for example, high porosity with good mechanical properties), leave limited options for designing MD membranes in commercial applications
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