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Cracking the Mystery of Polyelectrolyte Coacervate Structure and Dynamics

破解聚电解质凝聚层结构和动力学之谜

基本信息

批准号：
2100513
负责人：
Ronald Larson
金额：
$ 50.02万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-09-01 至 2025-08-31
项目状态：
未结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2100513&HistoricalAwards=false
关键词：
Cracking Mystery Polyelectrolyte Coacervate Structure

项目摘要

PART 1: NON-TECHNICAL SUMMARYPolyelectrolyte complexes are a mixture of two kinds of electrically charged, long polymer molecules, of opposite charge. Their opposite charge causes the two kinds of polyelectrolytes, which can be very different from each other, to nevertheless attract each other and form an intimate mixture, or complex. An important example of a polyelectrolyte complex is the chromosome, which contains DNA, which is a negatively charged polymer and hence repels itself. Nature therefore uses positively charged proteins to bind to the DNA and bundle it into the compact shape of the chromosome. Among the many other examples of polyelectrolyte complexes are biological membranes, underwater adhesives, drug delivery vehicles, and food processing agents. Despite their importance and the growing interest in them for advanced applications, basic understanding of how to control their structure and mechanical properties remains undeveloped. The proposed work focuses on measurements of the mechanical properties of these complexes, such as their viscosity and stiffness, and computer simulations to determine how these properties are controlled by the composition, including the polyelectrolytes, salts, and pH. Understanding the relationship between the composition and mechanical properties will provide deep insight into why complexes have the properties they do, and how to design these properties for future applications. There may also be connections to biological function, which are affected by the micro-mechanical properties of these complexes. The research will be integrated with education of graduate and undergraduate students, outreach, and creation of software.PART 2: TECHNICAL SUMMARYThe PI and his group will measure the linear rheology of polyelectrolyte coacervates of widely varying composition and containing different salts, and seek to test time-temperature, time-salt, time-hydration, and time-pH superpositions that allow data to be collapsed onto approximate “master curves.” Specifically, they will measure the linear rheological properties of polycations poly(N,N-dimethylaminoethyl methacrylate) and poly(diallyldimethylammonium) with polyanions poly(acrylic acid) and poly(styrene sulfonate), and with salt ions Na+ or K+, and Cl- or Br-. They will explore the surprising differences and anomalies among coacervates, depending on the polyelectrolytes, salts, and the chain lengths used, including an asymmetry in relaxation time produced by changing the molecular weight of polyanion vs. polycation, anomalous dependence of viscosity on degree of polymerization, and a low-frequency plateau modulus for some, but not all, coacervates. The systematic approach will provide a comprehensive understanding of the key determinants of rheological behaviour and overcome the limitations of existing data sets. They will also carry out molecular dynamics simulations to determine the nature of the local interactions among polyelectrolytes and salt ions that determine the rates of relaxation. This will be done in part through development of novel time correlation functions to determine whether local monomer diffusion is governed by ion-pairing dynamics, or by collective “glassy” dynamics, or some mixture of the two..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.

第1部分：非技术概述聚电解质复合物是两种电荷相反的长聚合物分子的混合物。它们的相反电荷导致这两种聚电解质，它们可以彼此非常不同，但仍然相互吸引并形成紧密的混合物或复合物。一个重要的例子是染色体，其中含有DNA，这是一个带负电荷的聚合物，因此排斥自己。因此，自然界使用带正电荷的蛋白质与DNA结合，并将其捆绑成染色体的紧凑形状。生物膜、水下粘合剂、药物递送载体和食品加工剂是生物复合物的许多其他例子。尽管它们的重要性和对它们在高级应用中的日益增长的兴趣，但对如何控制它们的结构和机械性能的基本理解仍然没有发展。拟议的工作重点是测量这些复合物的机械性能，如它们的粘度和刚度，以及计算机模拟，以确定这些性能是如何由组合物控制的，包括聚电解质，盐和pH值。了解组合物和机械性能之间的关系将深入了解为什么复合物具有它们的性能，以及如何为未来的应用设计这些特性。也可能与生物功能有关，这些生物功能受到这些复合物的微观机械特性的影响。该研究将与研究生和本科生的教育，推广和软件的创建相结合。第2部分：技术总结PI和他的团队将测量组成广泛变化并含有不同盐的微凝聚层的线性流变学，并试图测试时间-温度，时间-盐，时间-水合和时间-pH叠加，使数据可以折叠到近似的“主曲线”上。具体来说，他们将测量聚阳离子聚（甲基丙烯酸N，N-二甲基氨基乙酯）和聚（二烯丙基二甲基铵）与聚阴离子聚（丙烯酸）和聚（苯乙烯磺酸盐）以及盐离子Na+或K+的线性流变性能，以及Cl-或Br-。他们将探索凝聚体之间令人惊讶的差异和异常，这取决于所使用的聚电解质，盐和链长，包括通过改变聚阴离子与聚阳离子的分子量产生的弛豫时间的不对称性，聚合度对粘度的异常依赖性，以及一些但不是所有凝聚体的低频平台模量。系统的方法将提供流变行为的关键决定因素的全面理解，并克服现有数据集的局限性。他们还将进行分子动力学模拟，以确定聚电解质和盐离子之间的局部相互作用的性质，这些相互作用决定了弛豫速率。这将部分通过开发新的时间相关函数来确定局部单体扩散是否受离子配对动力学或集体“玻璃态”动力学或两者的某种混合物控制。该奖项反映了NSF的法定使命，并被认为是值得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的支持。