Polyelectrolyte Phase Behavior and Transport

非技术概述：带电聚合物，称为聚电解质，在生物学中很常见，包括DNA， RNA，蛋白质和粘膜层。它们越来越多地用于从药物输送到传感膜或电池的应用。用于这些应用的聚电解质膜可以通过依次将表面浸入带负电的聚电解质中，然后浸入带正电的聚电解质中，一层一层地构建起来。此外，被水膨胀的凝胶，被称为“凝聚体”，可以通过混合两种相反带电的聚电解质来制成。尽管这些材料在生物学和高级应用中具有重要意义，但人们对它们的行为知之甚少，目前既不了解凝聚体的性质，也不了解逐层膜的生长速度。虽然最近已经开发出了这种多电解质材料的有希望的理论，但很少有系统的实验数据来测试和证实这些理论，从而帮助设计先进的材料。为了提供这样的测试，本项目将使用简单和先进的实验方法来测量凝聚体的组成，以及逐层薄膜的生长速度和厚度。这些测量将在不同的盐浓度和pH值下系统地进行，以建立测试和确认新开发的理论所需的定量趋势，并为设计由聚电解质制成的先进材料提供坚实的基础。这些知识也与生物系统有关，包括带正电的蛋白质与带负电的DNA的相互作用，这控制着染色体的结构和功能。除了研究之外，这个项目更广泛的影响将包括研究生和本科生的教育，推广，以及与这个主题相关的专业计算代码的开发。技术概述：为了理解和测试理论的平衡和动力学组装的相反带电的聚电解质，几个阶段的研究将进行。首先，将通过高压液相色谱、质子核磁共振和其他方法测量四种常见聚电解质混合物的相行为，包括凝聚相和上清相中单个多离子的组成。这些结果将与新理论的预测进行比较，并用于测试和改进这些理论。酸和碱滴定将用于确定离子配对平衡常数，电离平衡和热力学“chi”参数。此外，这些聚电解质的逐层生长速率将被测量，由理论和相行为确定的热力学信息将用于预测这些生长速率。预测LbL生长所需的聚电解质多层膜中多离子的扩散率将从离子配对的强度中推断出来，离子配对的强度来自于水和盐中聚阴离子和多阳离子的原子分子动力学（MD）模拟。

NON-TECHNICAL SUMMARY:Electrically charged polymers, called polyelectrolytes, are common in biology and include DNA, RNA, proteins, and mucous layers. They are increasingly used for applications ranging from drug delivery to membranes for sensing or batteries. Membranes of polyelectrolytes for these applications can be built up, layer by layer, by sequentially dipping a surface into a negatively charged polyelectrolyte followed by dipping into a positively charged one. Additionally, gels swollen with water, known as "coacervates", can be made by mixing two oppositely charged polyelectrolytes. Despite the importance of these materials in biology and advanced applications, their behavior is poorly known, and neither the properties of coacervates nor the rate of growth of layer-by-layer membranes is understood at present. While promising theories for such polyelectrolyte materials have recently been developed, there is little systematic experimental data to test and confirm these theories so as to help design advanced materials. To provide such tests, this project will use both simple and advanced experimental methods to measure the composition of coacervates, and the growth rate and thickness of layer-by-layer films. These measurements will be carried out systematically with varying salt concentration and pH to establish quantitative trends needed to test and confirm newly developed theory and provide a firm base for design of advanced materials made from polyelectrolytes. Such knowledge is also relevant in biological systems, including the interactions of positively charged proteins with negatively charged DNA, which controls the structure and function of chromosomes. Beyond the research, broader impacts of this project will include the education of graduate and undergraduate students, outreach, and development of specialized computational codes relevant to this topic.TECHNICAL SUMMARY:To understand and test theories for the equilibrium and dynamics of assemblies of oppositely charged polyelectrolytes, several phases of study will be performed. First, the phase behavior including compositions of individual polyions in both coacervate and supernatant phases for four common polyelectrolyte mixtures will be measured by high pressure liquid chromatography, proton NMR, and other methods. The results will be compared to the predictions of new theories, and used to test and improve these theories. Titrations with acid and base will be used to determine ion pairing equilibrium constants, ionization equilibrium, and thermodynamic "chi" parameters. In addition, Layer-by-Layer (LbL) growth rates for these polyelectrolytes will be measured and the thermodynamic information determined by theory and phase behavior will be used to predict these growth rates. The diffusivities of polyions through the polyelectrolyte multilayer needed for predictions of LbL growth will be inferred from strengths of ion pairing obtained from atomistic molecular dynamics (MD) simulations of a polyanion and polycation in water and salt.