pH-Responsive Polymer Films and Surfaces

该项目将开发新型共聚物和自组装单层膜，通过显著改变屏障和/或表面特性来响应pH值。共聚物薄膜是通过一种独特的表面催化聚合物薄膜生长制备的，这种聚合物薄膜的厚度可调，从~20到1000纳米不等，其成分可高度控制，并且可以在金表面上选择性生长。PI实验室最近的工作表明，在低温下，将金表面暴露在重氮甲烷（DM）和重氮乙酸乙酯（EDA）的稀释溶液中，会导致一种新型共聚物膜的受控、催化生长，该共聚物膜主要含有线性聚乙烯（PM）和随机乙基酯侧基。酯侧基团可以水解成羧酸，当pH值增加时，羧酸会被去质子化或电离，起到pH响应门的作用。这种反应性聚合物薄膜在化学和生物传感器、动态表面和智能膜方面有着广泛的应用。提出的方案提供了分子定制膜和表面组成的新方法，以影响ph诱导反应的开始、大小和速率。该项目建立在这些成功的初步结果的基础上，以开发(1)一种新的ph响应共聚物薄膜，具有不同的“开启”值；(2)ph敏感的“触发器”基团，可以附着在聚合物表面或自组装硫醇吸附剂上，从而产生表面能在ph诱导下发生大变化的界面。本文所述的工作将通过检查(i)侧链组成和浓度对聚合物屏障特性中ph诱导响应的开始、大小和速率的作用，（ii）疏水三氟甲基对ph响应表面基团的可切换特性的影响，来推进智能薄膜和界面领域的基础知识。（iii）通过使用外加电位改变局部pH值来主动控制这些薄膜和界面的响应的能力。在这些目标中，拟议的工作将确定薄膜厚度和均匀性对水渗透速率和机制的影响，并指导薄膜的生长以产生图案特征，这些特征可以放大pH值或电位驱动的表面性质转变的幅度。综上所述，这些目标将确定能够放大薄膜表面和屏障性能响应的薄膜成分，并将开发出主动控制薄膜性能的新方法。建议活动的更广泛影响该计划将把研究和教育结合起来，为本科生，特别是少数族裔学生提供机会，获得智能电影/界面的研究经验，并为从大一到研究生阶段的五门不同课程开发新的学习材料。该项目包括动力学、质量传递和分子设计的各个方面，这些内容将作为案例研究、例子和作业问题纳入讲座中，以磨练化学工程和跨学科学生的分子直觉。除了一名研究生外，该项目还将通过提供研究助理奖学金，在三个暑假里支持三名本科生。通过他们的工作，本科学生将实现在课堂上学到的概念，并发现智能材料设计的分子水平方法。通过这项研究，学生们将发展出一种增强的分子直觉，并将对科学过程有一个坚实的理解。

ABSTRACTVanderbilt University - 0522937The proposed project will develop new classes of copolymer and self-assembled monolayer films that respond to pH by dramatically altering barrier and/or surface properties. The copolymer films are prepared by a unique surface-catalyzed polymer film growth that enables tunable film thicknesses from ~20 to 1000 nm, highly controlled compositions, and selective growth on gold surfaces. Recent work from the PI's laboratory has shown that exposure of gold surfaces to dilute solutions of diazomethane (DM) and ethyl diazoacetate (EDA) at low temperature results in a controlled, catalyzed growth of a novel copolymer film containing predominately linear polymethylene (PM) with random ethyl ester side groups. The ester side groups can be hydrolyzed to carboxylic acids that become deprotonated or ionized upon increases in pH to function as a pHresponsive gate. Such responsive polymer films have broad applications in chemical and biological sensors, dynamic surfaces, and smart membranes. The proposed plan provides new approaches to molecularly tailor film and surface composition to affect the onset, magnitude, and rate of the pHinduced response. Intellectual MeritThe proposed project builds from these successful initial results to develop (1) a new pH-responsive copolymer film that exhibits a different "turn-on" value, and (2) pH-sensitive "flip-flop" groups that can be attached to polymer surfaces or onto self-assembling thiol adsorbates to yield interfaces that exhibit large pH-induced changes in surface energy. The work described herein will advance fundamental knowledge in the area of smart films and interfaces by examining the (i) the role of side chain composition and concentration on the onset, magnitude, and rate of the pH-induced response in polymer barrier properties, (ii) the effect of hydrophobic trifluoromethyl groups on the switchable properties of pH-responsive surface groups, (iii) the ability to actively control the response of these films and interfaces by use of applied potential to alter the local pH. Within these aims, the proposed work will determine the effect of film thickness and uniformity on the rate and mechanism of aqueous permeation and direct the growth of the films to yield patterned features that amplify the magnitude of pH- or potential-driven transformations in surface properties. Combined, these aims will identify film compositions that magnify film response in both surface and barrier properties and will develop new approaches to actively control film properties.Broader Impacts Resulting from the Proposed ActivityThe project will integrate research and education by providing opportunities for undergraduates, especially minority students, to gain research experience in smart films/interfaces and by developing new learning materials in five different courses from the freshman level to the graduate level. The project comprises aspects of kinetics, mass transport, and molecular design that will be incorporated into lectures as case studies, examples, and homework problems to hone the molecular intuition of chemical engineering and interdisciplinary students. In addition to a graduate student, the project will support three undergraduate students over three summers by providing research assistantships. Through their work, the undergraduate students will implement concepts learned in the classroom and discover molecular-level approaches to the design of smart materials. Through this research, the students will develop an enhanced molecular intuition and will gain a solid understanding of the scientific process.