Polyelectrolyte Phase Behavior and Transport

非技术摘要：带电聚合物，称为聚电解质，在生物学中很常见，包括DNA、RNA、蛋白质和粘液层。它们越来越多地被用于从药物输送到传感薄膜或电池的应用。通过将表面依次浸入带负电荷的聚电解质中，然后再浸入带正电荷的聚电解质中，可以一层又一层地建立用于这些应用的聚电解质的膜。此外，用水溶胀的凝胶，也就是所谓的“凝聚物”，可以通过混合两种相反电荷的聚电解质制成。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，目前还不清楚凝聚体的性质和逐层膜的生长速度。虽然最近出现了一些有希望的理论，但很少有系统的实验数据来验证和证实这些理论，从而帮助设计先进的材料。为了提供这样的测试，这个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下系统地进行，以建立检验和确认新发展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。这样的知识在生物系统中也是相关的，包括正电荷蛋白质与负电荷DNA的相互作用，DNA控制着染色体的结构和功能。除了研究之外，这个项目的更广泛的影响将包括对研究生和本科生的教育，推广，以及与这个主题相关的专门计算程序的开发。技术总结：为了理解和测试相反电荷聚电解质组装的平衡和动力学理论，将进行几个阶段的研究。首先，我们将用高压液相色谱、质子核磁共振等方法测量四种常见的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。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。酸碱滴定将被用来确定离子配对平衡常数、电离平衡和热力学“X”参数。此外，还将测量这些聚电解质的逐层生长速率，并将使用由理论和相行为确定的热力学信息来预测这些生长速率。预测LBL生长所需的聚离子通过聚电解质多层膜的扩散系数将从水和盐中聚阴离子和聚阳离子的原子分子动力学(MD)模拟获得的离子对强度推断出来。

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.