Star-Shaped and Linear Polymers in Temperature-Responsive Layer-by-Layer Assemblies

对环境刺激有反应的功能性聚合物涂层可用于生物医学、农业、海洋和食品应用。作为对刺激的响应，这些涂层可以改变水或药物分子的吸收，从而提供表面自清洁、药物释放或防污性能的控制。该项目采用温度作为控制表面涂层行为的最普遍的刺激之一。当涂层沉积在缝线或假体植入物表面时，这种涂层可以根据体温升高输送药物（如麻醉剂或抗生素），或者当涂层沉积在窗户或船只的大表面时，它们可以根据需要使表面不粘连。反应性涂层还可以延长食物的保质期，防止食物在炎热的天气里腐烂。然而，挑战在于如何制造出对温度升高有最大响应的涂层。该项目将利用PI是专家的层层（LbL）技术的能力，在各种表面上创建厚度可控的保形涂层，并将探索组装分子的各种复杂分子结构（对涂层功能的影响）。先进的仪器技术将用于拍摄多层结构，含水量和聚合物薄膜机械性能如何响应温度变化的快照。重要的是，这个项目将为参与的研究生、本科生和高中生创造一个肥沃的训练场地。PI目前是“材料科学女性”（WIMS）组织的学术顾问，该组织积极参与许多外展活动，包括学校教师的校园参观和女童子军和高中生的示范，以及访问当地学校，目的是鼓励和吸引5-7年级的学生从事科学和工程方面的职业。第二部分：技术概述通过不同聚合物组分的组装形成高功能表面的能力是先进生物医学、海洋和食品应用的核心。本研究研究了层接层（LbL）组装，旨在揭示响应材料在表面组装的主要基本原理，特别关注分子结构对膜结构和响应的作用。重点将放在未开发的高临界溶液温度（UCST）星形聚合物在溶液和LbL膜内的区域。ucst型LbL薄膜提供了一种非常实用的途径来调节表面顺应性，控制与细胞或污染物的相互作用，并调节被捕获的小功能分子的释放，以响应环境温度的升高。然而，挑战在于如何平衡纳米容器对温度的响应性（随着星形功能的增加而降低，即臂数f），以及与LbL薄膜内线性聚合物链的结合强度，以便最大限度地提高薄膜的响应性和作为受控递送平台的性能。本项目旨在通过星形聚合物的分子参数（f，以及臂上的单元数N）与聚合物星形聚合物及其组件的响应性之间的关系来探索星形聚合物的UCST响应机制，从而解决这一挑战。该项目涉及新型UCST星形聚合物的合成，利用等温滴定量热法、动态光散射、荧光相关和振动光谱法对星形聚合物与氢键聚合物伴侣的组装进行溶液研究，以及几种正交技术的应用，如中子反射法、光漂白后荧光恢复、原位椭偏法、和纳米压痕，探索LbL含星薄膜的组装和温度响应。该项目的主要成果将是开发星形聚合物的分子参数与它们在溶液中的UCST响应、LbL膜内的扩散率以及最终的膜结构和响应相关的知识。这些知识将用于合理地构建具有可编程温度响应特性的薄膜。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 I: NON-TECHNICAL SUMMARY Functional polymer coatings that are responsive to environmental stimuli are useful for biomedical, agricultural, marine and food applications. In response to a stimulus, these coatings can change uptake of water or drug molecules, thus providing control of surface self-cleaning, drug-releasing or antifouling properties. This project employs temperature as one of the most ubiquitous stimuli for controlling behavior of surface coatings. When deposited at the surface of sutures or prosthetic implants, such coatings could deliver drugs (such as anesthetics or antibiotics) in response to increased body temperature, or they could render surfaces non-adhesive on-demand when deposited on large surfaces of windows or ships. Responsive coatings could also prolong the shelf life of food, preventing its rotting on hot days. The challenge is, however, to create such responsive coatings with maximized response to an increase in temperature. This project will take advantage of the capability of the layer-by-layer (LbL) technique, in which the PI is an expert, to create conformal coatings of controlled thickness on a variety of surfaces, and will explore the effect of various intricate molecular architectures of assembled molecules (on coating functionality. Advanced instrumental techniques will be used to take snapshots of how multilayered structures, water content, and polymer-film mechanical properties respond to temperature variations. Importantly, this project will create a fertile training ground for the participating graduate, undergraduate, and high-school students. The PI is currently the academic advisor of the "Women in Materials Science" (WIMS) organization, which is strongly involved in many outreach activities, including on-campus tours for school teachers and demonstrations for Girl Scouts and high-school students, as well as visits to local schools with the goal of encouraging and engaging 5-7th graders to pursue careers in science and engineering.PART II: TECHNICAL SUMMARYThe ability to form highly functional surfaces by means of assembly of diverse polymeric components lies at the heart of advanced biomedical, marine and food applications. This research studies layer-by-layer (LbL) assemblies and aims to uncover the main underlying principles of assembly of responsive materials at surfaces, specifically focusing on the role of molecular architecture on film structure and response. The focus will be on the unexplored area of upper critical solution temperature (UCST) star-shaped polymers in solution and within LbL films. UCST-type LbL films enable a highly practical route to modulate surface compliance, control interactions with cells or contaminants, and regulate release of trapped small functional molecules in response to an increase in environmental temperature. The challenge is, however, to balance responsiveness of nanocontainers to temperature (which tends to decrease with an increase in star functionality, i.e. number of arms f), with strength of binding with linear polymers chains within LbL films, in order to maximize film responsiveness and performance as a platform for controlled delivery. This project aims to address this challenge by exploring the mechanism of UCST response of star-shaped polymers through the relationships between molecular parameters of the star (f, as well as number of units in the arm N) and responsiveness of polymer stars and their assemblies. The project involves synthesis of novel UCST star polymers, solution studies of assembly of star polymers with hydrogen-bonding polymer partners using isothermal titration calorimetry, dynamic light scattering, fluorescence correlation and vibrational spectroscopies, as well as application of several orthogonal techniques, such as neutron reflectometry, fluorescence recovery after photobleaching, in situ ellipsometry, and nanoindentation to explore assembly and temperature response of LbL star-containing films. The main outcome of the project will be the development of the knowledge relating molecular parameters of the star polymer to their UCST response in solution, diffusivity within LbL films, and the resultant film structure and response. This knowledge will then be used to rationally construct films with programmable temperature -esponse characteristics. .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.