Hydrophobicity versus Pore Size: Polymer Coatings to Improve Membrane Wetting Resistance for Membrane Distillation
Hydrophobicity versus Pore Size: Polymer Coatings to Improve Membrane Wetting Resistance for Membrane Distillation
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DOI：
10.1021/acsapm.9b01133
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发表时间：
2020-03-01
影响因子：
5
通讯作者：
Childress, Amy E.
中科院分区：
文献类型：
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作者：
McGaughey, Allyson L.;Karandikar, Prathamesh;Childress, Amy E.
采用引发化学气相沉积（iCVD）技术，在两种多孔基底（亲水性醋酸纤维素（CA）和疏水性聚四氟乙烯（PTFE））上涂覆交联氟聚合物，以提高膜的抗润湿性。涂覆的CA膜具有超疏水性和对称性。涂覆后的PTFE膜具有疏水性和不对称性，上表面孔径较小，孔隙率低于下表面。采用(1)高盐度进料溶液和(2)含表面活性剂进料溶液进行膜蒸馏实验，测试膜的性能。在这两种情况下，涂覆的膜比未涂覆的膜具有更高的耐湿性。值得注意的是，LEP分布比最小LEP值更能预测润湿阻力。当LEP分布向高LEP值倾斜时（即高LEP的小孔隙数量较多），不会发生显著的（可测量的）盐通道。对于高盐度进料溶液，涂覆PTFE膜比涂覆CA膜具有更大的耐湿性；因此，减少表面孔径/孔隙率（可能减少孔内结垢）比增加表面疏水性（可能减少表面成核）在防止结垢引起的润湿方面更有效。在抵抗表面活性剂引起的润湿方面，减小孔径/孔隙度与增加疏水性同样有效。然而，孔隙度降低会对水通量产生负面影响；这代表了膜蒸馏中渗透性和润湿性的权衡，特别是在高盐度应用中。必须优化膜和/或膜涂层性能，以克服渗透性和润湿性之间的权衡，并使MD能够用于处理具有挑战性的流体。因此，增加疏水性可能并不需要赋予多孔膜高的抗润湿性。这些结果对未来的膜设计很重要，特别是当制造商寻求用环保替代品取代全氟材料时。
Initiated chemical vapor deposition (iCVD) was used to coat two porous substrates (hydrophilic cellulose acetate (CA) and hydrophobic polytetrafluoroethylene (PTFE)) with a cross-linked fluoropolymer to improve membrane wetting resistance. The coated CA membrane was superhydrophobic and symmetric. The coated PTFE membrane was hydrophobic and asymmetric, with smaller pore size and lower porosity on the top surface than on the bottom surface. Membrane performance was tested in membrane distillation experiments with (1) a high-salinity feed solution and (2) a surfactant-containing feed solution. In both cases, the coated membranes had higher wetting resistance than the uncoated membranes. Notably, wetting resistances were better predicted by LEP distributions than by minimum LEP values. When LEP distributions were skewed toward high LEP values (i.e., when small pores with high LEP were greater in number), significant (measurable) salt passage did not occur. For the high-salinity feed solution, the coated PTFE membrane had greater wetting resistance than the coated CA membrane; thus, reduced surface pore size/porosity (which may reduce intrapore scaling) was more effective than increased surface hydrophobicity (which may reduce surface nucleation) in preventing scaling-induced wetting. Reduced pore size/porosity was equally as effective as increased hydrophobicity in resisting surfactant-induced wetting. However, reduced porosity can negatively impact water flux; this represents a permeability/wetting resistance trade-off in membrane distillation-especially for high-salinity applications. Membrane and/or membrane coating properties must be optimized to overcome this permeability/wetting resistance trade-off and make MD viable for the treatment of challenging streams. Then, increasing hydrophobicity may not be necessary to impart high wetting resistance to porous membranes. These results are important for future membrane design, especially as manufacturers seek to replace perfluorinated materials with environmentally friendly alternatives.