水在油下特殊表面涂层上的润湿性和聚并分离相关性的研究

Emulsified water separation from oil in the presence of surfactants by physical means is a difficult problem. One example is to remove such water effectively from ultralow sulfur diesel fuel, which is of significant importance for advanced engine protection and motor tail pipe emission control. Coalescence is one of those economical separation methods commonly accepted by end users. However, its performance is seriously challenged by surfactants that lead to increased emulsion stability and material surface property disarming. In fact, the interfacial behavior of surfactants manipulates the affinity of water to the coalescence material, thus effective oil/water separation is difficult to achieve. In a liquid-liquid-solid system, the adsorption of surfactants at the interfaces of liquid-liquid and liquid-solid affects the wetting behavior of water on the solid. Such dynamic behavior cannot be derived without question based on the interaction between water and the same solid surface in air. A solid surface with certain chemistries can, as observed, abnormally benefit its water affinity by, as theorized, preventing or abating surfactant invasion to enhance the water separation efficiency. However, it is unclear how such abnormal behavior really works scientifically; the theory needs to be validated. Therefore, it is the objective of this project to study in depth such special interfacial behavior, and find out its scientific relevance to coalescence separation of water-in-oil emulsions, providing subsequently the basis of coalescence material design, and further extending the findings to the many water/oil separation applications.

在有表面活性剂存在的情况下，以物理法从油中去除乳化水是一个难题。比如从超低硫含量的柴油中高效率脱除这类水，对先进发动机的保护和减少尾气排放都至关重要。聚并除水法是经济的且易为用户接受的方法之一， 然而表面活性剂使乳化水的稳定性提高，使材料本身表面性质改变，从而使该方法失去除水的效果。事实上，表面活性剂的界面行为控制水对聚并材料的亲和性而使油水难以被有效地分离。液-液-固体系中表面活性剂在液-液和液-固界面上的吸附影响水对固体表面的润湿性，这种动态润湿性很难以水在空气中对固体表面的相互作用来推断。据观察，固体表面的某些化学对水在它表面上的亲和有利，理论上可防止或减轻表面活性剂的攻击而强化油水分离效果，然而这种异常行为尚缺乏科学解释和理论证明。本课题拟对这种特殊的界面行为进行深入的研究， 并期望找到它与聚并分离油包水乳液的科学关联，为聚并材料提供设计基础，进一步推广到众多的油水分离应用。

该项目针对柴油发动机上乳化水分离难的问题进行基础研究，期望通过对聚结分离材料的表面改性，得到合适的油水浸润性，从而使材料能够对添加到柴油中的表面活性剂类助剂不敏感，保证材料的有效分离效率。同时对可能的表面涂层化学进行选择和设计，解析其结构，了解其破乳机制，从而为设计这类材料提供科学指导。经过研究发现，多种氟碳涂层和硅氧烷等涂层对聚结材料的分离并无帮助，且使效率在表活剂存在的情况下下降。然而其中一种氟碳涂层在油下表现出特殊的浸润性，水在该涂层上的动态接触角不断下降，进而导致所涂覆材料的聚结效率在表活剂存在的情况下保持稳定。对该涂层化学进行了详细分析，发现它是一种含氟聚氨酯，且含氟的碳链C-F长不超过4，为生物可降解的环境友好氟碳材料。以悬滴法对水在该涂层上的聚结机理进行了研究，发现这个涂层之所以能促进聚结的进行，与表面膜的形成及涂层对界面表活剂的竞争吸附有关。进一步地，对多种氟碳材料涂层进行了研究，发现表面能无法关联材料的聚结效率。研究了涂层在油下陈化对涂层浸润性的影响，进一步证实了有效涂层必须具备在油下抵抗表面活性剂吸附导致的非润湿行为。而所发现的氟碳聚氨酯具有在外界环境（水，柴油和表活剂）的诱导下， 使其极性集团暴露在表面的特性，从而与水直接接触，导致其不被期待的特殊润湿性，促进水液滴的聚结长大，进而使分离得到强化， 这个发现对于同类材料的设计有着极大的科学指导意义。