Manufacturing of Distillation Membranes with Controlled Microstructure Based on Atomistic and Continuum Theories

随着清洁水的获取成为全球关注的问题，现在比以往任何时候都更需要一种高效、可持续和负担得起的水净化方法。海水淡化是从咸水（如海水）中生产淡水。研究人员提出了一种新的方法，通过一种称为直接接触膜蒸馏（DCMD）的过程来制造用于海水淡化的纤维膜。这种制造方法使海水淡化膜的发展成为可能，在个人家庭系统中使用，屋顶的阳光可以用来加热盐水并产生纯净水，而将少量的水泵到屋顶的成本可以忽略不计。制备的dmd膜也可用于其他现有或潜在的应用，如食品和饮料生产以及化学和制药工业。计划开展STEM教育和外展活动，以提高公众对气候变化和可持续水净化方法需求的认识。研究人员的许多拓展活动将集中在与北卡罗来纳州立大学科学之家（Catalyst Program）合作，为自闭症学生开发课程和模块。煮沸是淡化海水最简单的方法。然而，烧开水需要大量的能量。或者，现成的工业废热或太阳能可以将盐水加热到足以启动蒸发。从温暖的海水中蒸发的水的速率受限于蒸汽从温暖的海水（热源）向寒冷的环境（热沉）移动的速率。通过使散热器尽可能靠近热源，可以增加水的蒸发速率，这缩短了蒸汽需要移动的距离，即增加了热梯度和浓度梯度。用一层能渗透水蒸气但不能渗透液态水的薄膜将汇和源分开是缩短距离最实用的方法。这被称为直接接触膜蒸馏（DCMD）。目前DCMD膜的主要问题是它们的孔隙率通常很低，导致水蒸气通过膜的传输很低。这个问题可以通过使用高孔隙率的电纺丝纤维膜来解决，但是孔隙率的增加通常伴随着更高的膜润湿失败的机会（即液态水穿透膜）。研究人员已经确定了膜润湿失败的根本原因，并提出了一种新的方法来解决这些问题。该项目的目标是设计和生产一种非常薄且多孔的DCMD膜，同时不渗透液态水。这些高效的DCMD膜具有成功淡化海水的潜力，即使海水只比环境温度略高。该研究方法将应用第一性原理计算机模拟（分子动力学和有限元模拟）和神经网络建模，结合独特的制造方法来设计电纺纤维膜的微观结构，以防止润湿失效。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With access to clean water becoming a global concern, the need for an efficient, sustainable, and affordable water purification method is now greater than ever. Desalination is the production of freshwater from saltwater (e.g., seawater). The investigators have proposed a novel approach to fabricate fibrous membranes for saltwater desalination via a process called Direct Contact Membrane Distillation (DCMD). The fabrication method enables the development of desalination membranes for potential use in individual household systems, where rooftop sunlight can be used to heat the saltwater and produce purified water for the negligible cost of pumping a small volume of water to the roof. The fabricated DCMD membranes can also be used in other existing or potential applications such as food and beverage production and in the chemical and pharmaceutical industries. STEM education and outreach activities are planned to raise public awareness about climate change and the need for sustainable water purification methods. Many of the investigators’ outreach activities will focus on developing courses and modules for autistic students in collaboration with the Science House at North Carolina State University (the Catalyst Program). Boiling is the easiest way to desalinate saltwater. However, boiling water requires a significant amount of energy. Alternatively, readily available industrial waste heat or solar energy can heat the saltwater enough to initiate evaporation. The rate of water evaporation from warm saltwater is limited by the rate at which vapor travels away from the warm water (heat source) to the cold surroundings (heat sink). The rate of water evaporation can be increased by bringing the heat sink as close as possible to the heat source, which shortens the distance that the vapor needs to travel, i.e., increases the thermal and concentration gradients. Separating the sink and source with a thin membrane that is permeable to vapor but impermeable to liquid water is the most practical way to shorten the distance. This is called Direct Contact Membrane Distillation (DCMD). The major problem with the current DCMD membranes is that their porosities are generally very low, resulting in low water-vapor transport across the membrane. This problem can potentially be addressed by using high-porosity electrospun fibrous membranes, but the increased porosity is often accompanied by a higher chance of membrane wetting failure (i.e., liquid water penetrating the membrane). The investigators have identified the root causes of membrane wetting failure and have proposed a novel approach to address them. The goal of this project is to design and produce a DCMD membrane that is very thin and porous and is simultaneously impermeable to liquid water. These high-efficiency DCMD membranes have the potential to successfully desalinate saltwater even when the saltwater is only slightly warmer than the environment. The research approach will apply first-principles computer simulations (molecular dynamics and finite element simulations) and neural network modeling coupled with a unique manufacturing method to engineer the microstructure of electrospun fibrous membranes against wetting failure.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.