Collaborative Research: Selective Flow through Membrane Pores with in situ Change of Wettability

该项目的目标是使用特殊的膜(具有非常小的孔/通道的过滤器)来分离油和水，这种膜通过施加电势来改变每种液体在膜表面的行为。油水分离的效率取决于这些组分中的每一个与膜的相互作用。例如，一种亲水性或亲水性的膜允许水通过，但拒绝油。然而，油最终会堵塞毛孔，阻止更多的水通过膜。如果膜可以暂时切换到亲油或亲油，让油通过，这个问题就可以解决。当油相很有价值时，这种可切换的功能将特别有用，例如在油水混合物丰富的原油生产中，或在油相和水相都很有价值的乳制品行业中。不幸的是，在操作过程中改变膜性质的能力很难实现。该项目将通过改变膜的表面性质来实现这一目标，该膜的分子可以随着电的变化而改变其取向。首先，将确定对电作出反应并导致亲水性或亲油性发生所需变化的分子。作为该项目的中间目标，将通过在膜表面涂覆控制水的分子来开发能够控制水流动的膜。通过在石油上涂上控制石油的分子，也可以对石油进行同样的处理。最终，通过包覆控制油和水的分子，油和水的流动将被控制，以根据需要分离油水混合物。通过在废水处理、节能燃料生产、乳制品加工等方面的应用，可切换膜将具有社会效益。此外，该项目将直接让本科生和研究生参与有影响力的、变革性的研究。研究人员和学生将反过来参加农村STEM K-12推广计划，努力培养能够解决未来问题的下一代科学家和工程师。考虑到能源效率、相对较低的材料成本及其破乳功能等因素，膜是高效油水分离的首选技术。膜以各种形式出现，由不同的聚合物或无机材料构成，其中添加了控制膜表面亲水性和/或亲油性的部分。然而，一旦膜的表面性质被设定为渗透水，它们就不能改变为渗透最终堵塞毛孔的油。设计一种将膜功能切换到油或水渗透和从油或水渗透的方法将缓解污染问题，并使油相能够收集。这种膜技术将有利于许多工业应用，包括通过低盐度注水提高石油采收率，或在油相有价值的乳制品行业。因此，研究人员提出了一种新的方法来选择性地控制水和油通过膜的流动；油和水的润湿性将通过与吸附的表面分子相互作用来控制，这些分子会随着外加电位的变化而改变构象。润湿性是控制液体通过孔隙流动的因素之一，此外还有几何形状和水力压头。从油水混合物中一次只能有选择地渗透一个相的膜将实现如下：(1)首先，将识别引起水和油与电的接触角变化较大的表面分子(控制分子)。在给定变化的情况下，将计算和制造最佳的液压和几何形状。(2)下一步，将制备一种具有最佳几何形状的涂覆有控水分子的膜。对于石油，也将做同样的准备。膜的分离性能以及表面分子的耐久性将被表征。(3)最后的项目目标是开发一种带有“控制阀”的膜，该膜上涂有两个同时调节油和水的润湿性的控制分子。将对这种杂化表面进行表征，并对膜的性能和耐用性进行评估。该项目的成功将为液-液分离提供一种新的方法，并增强进行研究的本科生和研究生的教育经验。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of this project is to separate oil and water using special membranes (filters with very small pores/passages) that change how each fluid behaves at the membrane surface by applying an electric potential. The efficiency of the oil-water separation depends on the interaction of each of these components with the membrane. For example, a hydrophilic, or water-loving, membrane lets water through but rejects oil. However, the oil eventually plugs the pores, preventing additional water from moving through the membrane. This problem could be resolved if the membrane could be temporarily switched to be oleophilic, or oil-loving, to let the oil through. This switchable functionality would be especially helpful when the oil phase is valuable, such as in crude oil production where oil-water mixtures are abundant, or in the dairy industry where both the oil and water phases are valuable. Unfortunately, the ability to change membrane properties during operation is very difficult to achieve. This project will accomplish this goal by changing the surface properties of the membranes with molecules that change their orientation with electricity. First, molecules that respond to electricity and result in the desired change in hydrophilicity or oleophilicity will be identified. As an intermediate goal for this project, a membrane capable of controlling the flow of water will be developed by coating water-controlling molecules onto the membrane surface. The same will be done for oil by coating with oil-controlling molecules. Eventually, by coating both oil- and water-controlling molecules, the flow of oil and water will be controlled to separate oil-water mixtures on demand. The switchable membranes will be of societal benefit through their application in wastewater treatment, energy-efficient fuel production, dairy processes, and many others. In addition, the project will directly involve undergraduate and graduate students in impactful, transformative research. The investigators and students will, in turn, participate in rural STEM K-12 outreach programs working to develop the next generation of scientists and engineers capable of solving the problems of tomorrow. Membranes are a preferred technology for efficient oil-water separation given factors such as energy efficiency, relatively low material costs, and their demulsifying function. Membranes appear in a variety of forms constructed from different polymers or inorganic materials with added moieties that control hydrophilicity and/or oleophilicity of the membrane surfaces. However, once the surface properties of membranes are set to permeate water, they cannot be changed to permeate the oil that eventually clogs the pores. Devising a way to switch membrane functionality to and from oil- or water-permeating will mitigate fouling issues and enable collection of the oil phase. Such membrane technology would benefit many industrial applications, including enhanced oil recovery with low-salinity water flooding or the dairy industry where the oil phase is valuable. Therefore, the investigators propose a new way to selectively control water and oil flow through the membrane in situ; wettability of oil and water will be controlled through interactions with adsorbed surface molecules that change conformation with applied electric potentials. Wettability is one of the factors that control liquid flow through pores, along with the geometry and hydraulic head. Membranes that can selectively permeate only one phase at a time from oil-water mixtures will be achieved as follows: (1) First, the surface molecules that produce large changes in the contact angle of water and oil with electricity (“controlling molecules”) will be identified. The optimal hydraulic pressure and geometry with the given changes will be calculated and fabricated. (2) Next, one membrane with the optimal geometry coated with the water-controlling molecules will be prepared. The same will be prepared for oils. The separation performance of the membranes as well as the durability of surface molecules will be characterized. (3) The final project objective is to develop a membrane with "control valves" coated with two controlling molecules that modulate the wettability of oil and water simultaneously. This hybridized surface will be characterized, and membrane performance and durability will be assessed. The success of this project will enable a new approach to liquid-liquid separation and enhance the educational experiences of the undergraduate and graduate students conducting the research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.