Distribution of low-molecular weight ions in charged hydrogelsin equilibrium and under the application of external stimuli

带电水凝胶平衡和外部刺激下低分子量离子的分布

• 批准号: 268449726
• 负责人: Professor Dr. Christian Holm
• 金额: --
• 依托单位: Institut für Computerphysik (ICP)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/268449726?language=en
• 关键词: Distribution; low; molecular; weight; ions

Polyelectrolyte hydrogels, often referred to as superabsorbent polymers, consist of interconnected charged polymer strands which form a three-dimensional network. They exhibit a high affinity to water and are widely used in hygiene products, pharmaceutics, agriculture and food protection, mainly due to their high swelling capabilities. In the previous funding period we demonstrated an additional feature: Swollen polyelectrolyte hydrogels release salt depleted water when compressed by an external mechanical force. We exploited this behavior for a potential usage in a membrane-free desalination process and designed a novel experimental procedure to study the distribution of salt ions between a highly charged poly(sodium acrylate) gel phase and the external salt solution. The fundamental principle of the salt partitioning and consequently of the separation mechanism is based on the Donnan equilibrium where the fixed charges of the polyelectrolyte backbone cause an asymmetric distribution of mobile ions between the gel and supernatant phase, enabling the recovery of salt depleted water by compressing the gel. Based on our experimental results and hybrid Monte-Carlo and molecular dynamics simulations the Donnan theory was further extended to predict the salt partitioning and the desalination efficiency as the function of pressure and salt concentration. The energy demand for the desalination of a 35 g L-1 sodium chloride solution was estimated to be 8.9 kWh m-3, where the theoretical limit is 0.7 kWh m-3. Previous work indicated that a high charge density combined with low mechanical moduli are beneficial for the desalination efficiency, but the balance between swelling capability and mechanical strength for the compression procedure has not been optimized yet. Hence, in the second funding period the relation between swelling capacity and mechanical strength will be systematically studied. The charge density will be increased by incorporating non-elastic polymer components into the network, such as dangling ends or macromolecular objects (e.g. high-molecular weight polyelectrolyte chains, stars and dendrimers). Since the characterization of these multicomponent network structures on the molecular level is challenging, we will introduce 1H-NMR relaxometry as a characterization technique to determine the network structure by correlating topological features, e.g. dangling ends and crosslinking points, to their unique relaxation behavior. In combination with simulations that calculate the 1H homonuclear residual dipolar coupling constant by modulating the distance and relative orientation of protons, this technique will lead to a consistent fundamental understanding of the influence of molecular structure on macroscopic properties and the Donnan equilibrium. A description will emerge that can be utilized for the design and characterization of polyelectrolyte hydrogel materials with superior charge density and their application as separation medium.

聚电解质水凝胶通常称为超吸收性聚合物，由相互连接的带电聚合物链组成，形成三维网络。它们对水表现出高亲和力，主要由于其高溶胀能力而广泛应用于卫生用品、药品、农业和食品保护。在之前的资助期间，我们展示了一个附加功能：当受到外部机械力压缩时，膨胀的聚电解质水凝胶会释放出贫盐水。我们利用这种行为在无膜海水淡化过程中的潜在用途，并设计了一种新颖的实验程序来研究盐离子在高电荷聚（丙烯酸钠）凝胶相和外部盐溶液之间的分布。盐分配和分离机制的基本原理基于唐南平衡，其中聚电解质主链的固定电荷导致凝胶相和上清相之间的移动离子不对称分布，从而能够通过压缩回收贫盐水。凝胶。基于我们的实验结果以及混合蒙特卡罗和分子动力学模拟，唐南理论被进一步扩展以预测盐分配和海水淡化效率作为压力和盐浓度的函数。 35 g L-1 氯化钠溶液脱盐的能源需求估计为 8.9 kWh m-3，其中理论极限为 0.7 kWh m-3。先前的工作表明，高电荷密度与低机械模量相结合有利于海水淡化效率，但压缩过程的膨胀能力和机械强度之间的平衡尚未优化。因此，在第二资助期将系统地研究膨胀能力与机械强度之间的关系。通过将非弹性聚合物成分（例如悬空末端或大分子物体（例如高分子量聚电解质链、星形和树枝状聚合物））纳入网络中，可以增加电荷密度。由于在分子水平上表征这些多组分网络结构具有挑战性，我们将引入 1H-NMR 弛豫测量作为表征技术，通过关联拓扑特征来确定网络结构，例如拓扑特征。悬空末端和交联点，使其具有独特的松弛行为。结合通过调节质子的距离和相对方向来计算 1H 同核残余偶极耦合常数的模拟，该技术将导致对分子结构对宏观性质和唐南平衡的影响有一致的基本理解。将出现可用于具有优异电荷密度的聚电解质水凝胶材料的设计和表征及其作为分离介质的应用的描述。