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

随着获得清洁水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。海水淡化是从盐水中生产淡水（例如，海水）。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）的工艺制造用于盐水淡化的纤维膜。这种制造方法使脱盐膜的开发成为可能，可用于个人家庭系统，其中屋顶阳光可用于加热盐水并生产纯化水，而将少量水泵送到屋顶的成本可以忽略不计。所制造的DCMD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教育和外联活动，以提高公众对气候变化和可持续水净化方法必要性的认识。许多研究人员的外展活动将集中在与北卡罗来纳州州立大学的科学之家合作为自闭症学生开发课程和模块（催化剂计划）。煮沸是淡化盐水的最简单的方法。然而，烧水需要大量的能量。或者，容易获得的工业废热或太阳能可以加热盐水足以开始蒸发。水从暖盐水中蒸发的速率受到蒸汽从暖水（热源）向冷环境（散热器）移动的速率的限制。水蒸发的速率可以通过使散热器尽可能靠近热源来增加，这缩短了蒸汽需要行进的距离，即，增加了热梯度和浓度梯度。用一层对蒸汽可渗透但对液态水不可渗透的薄膜将汇和源分开是缩短距离的最实用的方法。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非常低，导致穿过膜的水蒸气传输低。这个问题可以通过使用高孔隙率的电纺纤维膜来潜在地解决，但是增加的孔隙率通常伴随着更高的膜润湿失效的机会（即，液态水渗透膜）。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和多孔的DCMD膜，同时对液态水不可渗透。这些高效DCMD膜具有成功淡化盐水的潜力，即使盐水仅略高于环境温度。该研究方法将应用第一原理计算机模拟（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，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NSF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.