Membrane distillation (MD) equipped with omniphobic (non-wetting) membranes has found a niche in water reclamation from hypersaline industrial wastewater. Here, we examined the efficacy of non-fluorinated materials as surface coating agents for omniphobic MD membrane fabrication, and identified necessary mechanisms to attain a maximized wetting resistance using fluorine-free materials. We first prepared MD membranes with different surface chemistries using a series of linear alkylsilanes and polydimethylsiloxane (PDMS) as representative fluorine-free, low surface energy materials. Membranes modified with a longer chain alkylsilane exhibited a lower surface energy and demonstrated a greater wetting resistance in direct contact MD experiments using feedwaters of various surface tensions. Despite the nearly identical surface energy measured for the longest alkylsilane and PDMS, PDMS-modified membrane exhibited an extended antiwetting performance as compared to the membrane treated with the longest alkylsilane. To elucidate the source of the distinctive wetting resistance, we examined the nucleation and condensation kinetics on the surfaces with the different surface chemistries via environmental scanning electron microscopy. Our analysis suggests that the membranes treated with long chain alkylsilanes contain surface defects (i.e., hydrophilic regions) whereas the high mobility of the PDMS effectively minimizes the defect exposure, slowing down the condensation and subsequent surface wetting.

中文翻译：

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最大化用于高盐废水淡化的无氟全疏膜的润湿性


配备全疏（非润湿）膜的膜蒸馏（MD）在高盐工业废水的水回收中找到了利基。在这里，我们研究了非氟化材料作为全疏MD膜制造的表面涂层剂的功效，并确定了使用无氟材料获得最大润湿性的必要机制。我们首先使用一系列线性烷基硅烷和聚二甲基硅氧烷（PDMS）作为代表性的无氟低表面能材料制备了具有不同表面化学性质的MD膜。用较长链烷基硅烷改性的膜表现出较低的表面能，并且在使用各种表面张力的给水的直接接触MD实验中表现出更大的润湿性。尽管最长的烷基硅烷和PDMS测得的表面能几乎相同，但与用最长的烷基硅烷处理的膜相比，PDMS改性的膜表现出更长的抗润湿性能。为了阐明独特的润湿性的来源，我们通过环境扫描电子显微镜检查了具有不同表面化学成分的表面上的成核和凝聚动力学。我们的分析表明，用长链烷基硅烷处理的膜含有表面缺陷（即亲水区域），而 PDMS 的高迁移率有效地最大限度地减少了缺陷暴露，减缓了冷凝和随后的表面润湿。