Engineering the Re-Entrant Hierarchy and Surface Energy of PDMS-PVDF Membrane for Membrane Distillation Using a Facile and Benign Microsphere Coating

Abstract

To consolidate the position of membrane distillation (MD) as an emerging membrane technology that meets global water challenges, it is crucial to develop membranes with ideal material properties. This study reports a facile approach for a polyvinylidene fluoride (PVDF) membrane surface modification that is achieved through the coating of the surface with poly(dimethylsiloxane) (PDMS) polymeric microspheres to lower the membrane surface energy. The hierarchical surface of the microspheres was built without any assistance of a nano/microcomposite by combining the rapid evaporation of tetrahydrofuran (THF) and the phase separation from condensed water vapor. The fabricated membrane exhibited superhydrophobicity-a high contact angle of 156.9° and a low contact-angle hysteresis of 11.3°-and a high wetting resistance to seawater containing sodium dodecyl sulfate (SDS). Compared with the control PVDF-hexafluoropropylene (HFP) single-layer nanofiber membrane, the proposed fabricated membrane with the polymeric microsphere layer showed a smaller pore size and higher liquid entry pressure (LEP). When it was tested for the direct-contact MD (DCMD) in terms of the desalination of seawater (3.5% of NaCl) containing SDS of a progressively increased concentration, the fabricated membrane showed stable desalination and partial wetting for the 0.1 and 0.2 mM SDS, respectively.

Robust superhydrophobic electrospun membrane fabricated by combination of electrospinning and electrospraying techniques for air gap membrane distillation

“…Additionally, the bead layer thickness, which was increased by increased the spinning volume leads to further reduction of the voids in the membrane structure, for instance, the porosity of ES15-2 reduced by 2.89%, whereas ES15-5 decreased by 11.47% compare with ES15 membrane. Similar results were reported by Lee et al [32] in which the porosity dropped from 89.5 to 72.4 % by modifying the electrospun membrane surface with a bead structure made from poly(dimethylsiloxane) and PVDF polymer. In contrast, Shahabadi et al [23] illustrated that the porosity of the modified membrane with 25µm thickness of beaded layer showed an insignificant change, with porosity percentage between 86 to 90%.…”

“…2c. This might be due to lower entanglement of the polymer chain due to use low polymer concentration as reported by Lee et al [32]. Additionally, the repulsion force between the polymer molecules, which has a positive charge, combined with the high surface tension of the polymer solution lead to creation of a beaded structure instead of more uniform fibre morphology.…”

“…Beside membrane pore size, LEP can be controlled by different parameters. According to the Young-Laplace equation [9], LEP is governed by membrane pore geometry, maximum pore size, membrane hydrophobicity which represented by liquid contact angle on the membrane surface and liquid solution surface tension [9,32,44]. It can be seen from Fig.…”

Performance Comparison between Polyvinylidene Fluoride and Polytetrafluoroethylene Hollow Fiber Membranes for Direct Contact Membrane Distillation

“…Pore wetting can significantly compromise the water flux and salt rejection of a DCMD system, leading to system failure. Inclusion of nanoparticles, such as PTFE, TiO 2 , SiO 2 , and carbon nanotube, and applications of extrinsic coatings with low surface energy have been investigated by researchers to increase the surface hydrophobicity of PVDF membranes, thereby reducing pore wetting [15,16,17,18,19,20,21,22,23,24,25,26]. These modifications, however, often suffer from complex manufacturing procedures, loss of the coatings in long-term operation, and potential health impact to human and the environment [27,28].…”

Structural tailoring of hierarchical fibrous composite membranes to balance mass transfer and heat transfer for state-of-the-art desalination performance in membrane distillation

“…Novel ENMs, represented by poly(vinylidene uoride-co-hexauoropropylene) (PH) exhibited a much higher water ux of 30-40 LMH compared to those of commercial membranes which had a water ux of 20-25 LMH under the same experimental conditions. [18][19][20] In addition, diverse strategies including surface modications via uorine containing agents [19][20][21] and inorganic nanoparticles (TiO 2 , 22,23 SiO 2 , 24,25 CNTs, [26][27][28] etc.) can be used to functionalize the ENMs and acquire superhydrophobic surfaces with a contact angle (CA) of more than 150 .…”