Water-driven Glass Transition Dynamics in Polyelectrolyte Complexes and Multilayers

第1部分：非技术概述带电聚合物（聚电解质）在从个人护理和能源到医疗保健等领域影响着社会。这些聚合物带有一个带电基团，可以与带相反电荷的大分子结合，形成一个更大的上层结构，称为聚电解质复合物。这些聚电解质如何结合的性质由结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，这些复合物应该在实际条件下具有所需的性能，例如特定的相对湿度值和温度。然而，对于水和温度如何以及为什么决定给定复合物的热性能和机械性能，仍然缺乏理解。一个重要的挑战是，目前尚不清楚这些物理性质如何与静电交联聚电解质复合物的原始结构联系起来。该项目通过研究不同环境条件下结构内聚电解质和水的动力学和流动性来解决这一挑战。这些发现将与结构的复杂性和物理性质如刚度进行比较。在这个项目中发展的知识可以导致一个预测关系，可以广泛地描述任何复杂的物理性质，以响应环境条件。拟议的工作为广大公众提供了多种教育丰富的机会。这项工作的教育目标和更广泛的影响包括：为本科生提供动手研究的机会，通过TAMU的化学开放日向公众展示K-12，在当地小学进行科学之夜演示，以及通过EngineerGirl网站进行在线推广。培养对多电解质复合物的物理性质的更深入的理解，因为它们连接到复合物的结构是推进其更广泛应用的一个重要挑战。然而，由于静电交联密度、含水量和温度等复杂因素，这种认识变得复杂。例如，已知玻璃化转变温度（Tg）与配合物内的水含量和离子配对密切相关，而水含量和离子配对又受到盐和/或ph的影响。然而，目前的理解多少是经验或定性的，需要与物理动态过程进行定量联系。该项目的中心目标是通过表征玻璃化转变动力学和复合物的分子结构来阐明玻璃化转变-配对-水关系的物理起源。这将通过光谱表征、动态力学分析和热分析来完成。这些复合物将进一步探讨其在不同时间尺度，温度和湿度值下的刚度。中心假设是聚合物链的动力学受到静电交联中的水迁移率和交联本身的结合/解离的影响。水可以润滑静电交联并促进静电交联的暂时解离。这项工作的一个重要成果可能是一种新的基于物理的理解，定量地将复杂结构和周围环境条件与该复杂结构的最终物理特性联系起来。该奖项反映了美国国家科学基金会的法定使命，并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，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.