Tackling membrane wetting is an ongoing challenge for large-scale applications of membrane distillation (MD). Herein, composite Janus MD membranes comprising an ultrathin dense hydrophilic layer are developed by layer-by-layer assembling cationic polyethyleneimine and anionic poly(sodium 4-styrenesulfonate) polyelectrolytes on a hydrophobic polyvinylidene fluoride substrate. Using surfactant-containing saline water as the feed with low surface tension, experiments reveal that the number of polyelectrolyte layers, rather than surface wettability or surface charge, determines the anti-wetting performance of the composite Janus membranes. More deposited layers yield higher wetting resistance. With the aid of positron annihilation spectroscopy, this study, for the first time, demonstrates the origin of the excellent wetting resistance of the composite Janus membranes. The effective pore size of the polyelectrolyte multilayer decreases with an increase in the number of the deposited layer. The membrane with an ultrathin hydrophilic multilayer of 48 nm has a sufficiently small pore size to sieve out surfactant molecules from the feed solution via a size exclusion mechanism, thus protecting the hydrophobic substrate from being wetted by the low-surface-tension feed water. This study may pave the way for developing next-generation anti-wetting Janus membranes for robust membrane distillation.

中文翻译：

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具有超薄致密亲水层的复合Janus膜能否在膜蒸馏中抗湿？

解决膜湿润对于膜蒸馏（MD）的大规模应用是一个持续的挑战。本文中，通过在疏水性聚偏二氟乙烯基材上逐层组装阳离子聚乙烯亚胺和阴离子聚（4-苯乙烯磺酸钠）聚电解质，开发了包含超薄致密亲水层的复合Janus MD膜。使用含表面活性剂的盐水作为低表面张力的进料，实验表明，聚电解质层的数量决定了复合Janus膜的抗湿性能，而不是表面可湿性或表面电荷。沉积的层越多，润湿性越高。借助正电子an没光谱学，这项研究首次实现了 证明了复合Janus膜优异的抗湿性的起源。聚电解质多层的有效孔径随着沉积层数的增加而减小。具有48nm超薄亲水多层的膜的孔径足够小，可以通过尺寸排阻机制从进料溶液中筛出表面活性剂分子，从而保护疏水性底物不被低表面张力的进水润湿。这项研究可能为开发下一代抗润湿的Janus膜铺平道路，以实现可靠的膜蒸馏。具有48nm超薄亲水多层的膜的孔径足够小，可以通过尺寸排阻机制从进料溶液中筛出表面活性剂分子，从而保护疏水性底物不被低表面张力的进水润湿。这项研究可能为开发下一代抗润湿的Janus膜铺平道路，以实现可靠的膜蒸馏。具有48nm超薄亲水多层的膜的孔径足够小，可以通过尺寸排阻机制从进料溶液中筛出表面活性剂分子，从而保护疏水性底物不被低表面张力的进水润湿。这项研究可能为开发下一代抗润湿的Janus膜铺平道路，以实现可靠的膜蒸馏。