Water-driven Glass Transition Dynamics in Polyelectrolyte Complexes and Multilayers

第1部分：非技术总结充电聚合物(聚电解质)在个人护理、能源和医疗保健等领域对社会产生影响。这些聚合物带有一个带电基团，可以与相反带电的大分子结合，形成一个更大的超结构，称为聚电解质络合物。这些聚电解质如何缔合的性质由缔合或静电交联的数量来表示，这反过来又影响络合物的物理性质。一个重要的挑战是，这些复合体应该在真实世界的条件下具有所需的特性，例如特定的相对湿度和温度。然而，对于水和温度如何以及为什么决定给定复合体的热和机械性质，仍然缺乏了解。一个重大的挑战是，尚不清楚这些物理性质如何与静电交联型聚电解质复合体的原始结构相联系。该项目通过研究在不同环境条件下聚电解质和结构内水的动力学和流动性来应对这一挑战。这些发现将与结构的复杂性和物理特性进行比较，如刚度。在该项目中开发的知识可以导致预测关系，该关系可以广泛地描述任何综合体的物理性质对环境条件的响应。拟议的工作为广大公众提供了几个教育丰富的机会。这项工作的教育目标和更广泛的影响包括：为本科生提供实践研究机会，通过TAMU的化学开放日向公众演示来推广K-12，在当地小学进行科学之夜演示，以及通过Engineering Girl网站进行在线推广。第2部分：技术总结培养更深入地了解聚电解质复合体的物理性质，因为它们与复合体的结构相连接，这是促进其更广泛应用的重要挑战。然而，由于静电交联密度、水分含量和温度等复杂因素，这种理解变得复杂起来。例如，众所周知，玻璃化转变温度(Tg)与水含量和络合物中的离子配对密切相关，而后者又受到盐和/或pH的影响。然而，目前的理解在某种程度上是经验性的或定性的，需要与物理动态过程建立定量联系。这个项目的中心目标是通过表征玻璃转变动力学和络合物的分子结构来阐明玻璃转变-离子对-水关系的物理起源。这将通过光谱表征、动态机械分析和热分析来完成。这些复合体将进一步探索它们在不同时间尺度、温度和湿度值下的硬度。中心假设是聚合物链的动力学受到静电交联处的水的流动性和交联物本身的缔合/解离的影响。水可以润滑静电交联物并促进静电交联物的暂时解离。这项工作的一个重要成果可能是一种新的基于物理学的理解，它将综合体的结构和周围环境条件与该综合体的最终物理属性定量地联系在一起。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYCharged polymers (polyelectrolytes) impact society in areas ranging from personal care and energy to health care. These polymers bear a charged group that can associate with oppositely charged macromolecules to form a larger superstructure called a polyelectrolyte complex. The nature of how these polyelectrolytes associate is represented by the number of associations or electrostatic crosslinks, which in turn influences the physical properties of the complex. One important challenge is that these complexes should bear desired properties at real-world conditions, such as certain relative humidity values and temperatures. However, there remains a lack of understanding regarding how and why water and temperature dictate the thermal and mechanical properties of a given complex. One significant challenge is that it is not clear how these physical properties connect to the original structure of the electrostatically crosslinked polyelectrolyte complex. This project addresses this challenge by examining the dynamics and mobility of the polyelectrolyte and of water within the structure at varying environmental conditions. These findings will be compared to the structure of the complex and physical properties such as stiffness. The knowledge developed in this project could lead to a predictive relationship that may broadly describe the physical properties of any complex in response to environmental conditions. The proposed work offers several opportunities for educational enrichment of a broad spectrum of members of the general public. The educational objectives and broader impact for this work include: hands-on research opportunities for undergraduates, K-12 outreach through TAMU's Chemistry Open House through demonstrations to the public, Science Night demonstrations at local elementary schools, and online outreach through the EngineerGirl website.PART 2: TECHNICAL SUMMARYCultivating a deeper understanding of the physical properties of polyelectrolyte complexes as they connect to the complex's structure is an important challenge for advancing their wider application. However, this understanding is complicated by complex factors such as the electrostatic crosslinking density, water content, and temperature. For example, it is known that the glass transition temperature (Tg) is intimately tied to the water content and ion pairing within the complex, which is in turn influenced by salt and/or pH. However, the current understanding is somewhat empirical or qualitative, and a quantitative connection to a physical dynamic process is needed. The central goal of this project is to elucidate the physical origin of the glass transition-ion pairing-water relationship via characterization of the glass transition dynamics and the molecular structure of the complex. This will be accomplished by spectroscopic characterization, dynamic mechanical analysis, and thermal analysis. These complexes will be further explored for their stiffness at different time scales, temperatures, and humidity values. The central hypothesis is that the dynamics of the polymer chain are influenced by water mobility at the electrostatic crosslink and by the association/dissociation of the crosslink itself. Water may lubricate the electrostatic crosslink and promote temporary dissociation of the electrostatic crosslink. One significant outcome of this work is possibly a new physics-based understanding that quantitatively connects the structure of a complex and the surrounding environmental conditions to the resultant physical properties of that complex..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.