pH-Responsive Polymer Films and Surfaces

Vanderbilt大学-0522937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/或表面性质来响应pH。该共聚物膜是通过独特的表面催化聚合物膜生长制备的，该聚合物膜生长能够实现约20至1000 nm的可调膜厚度、高度受控的组成以及在金表面上的选择性生长。PI实验室最近的工作表明，在低温下将金表面暴露于重氮甲烷（DM）和重氮乙酸乙酯（EDA）的稀溶液中，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亚甲基（PM）和随机乙酯侧基。酯侧基可以水解成羧酸，其在pH增加时变得去质子化或离子化以用作pH响应性门。这种响应性聚合物膜在化学和生物传感器、动态表面和智能膜中具有广泛的应用。拟议的计划提供了新的方法来分子量身定制膜和表面组成，以影响pH诱导反应的发生，幅度和速率。 知识产权优点建议的项目建立在这些成功的初步结果，以开发（1）一种新的pH响应共聚物膜，表现出不同的“打开”值，和（2）pH敏感的“触发器”基团，可以连接到聚合物表面或到自组装硫醇吸附产生界面，表现出大的pH诱导的表面能的变化。本文所述的工作将通过检查（i）侧链组成和浓度对聚合物阻隔性能中pH诱导的响应的起始、大小和速率的作用，（ii）疏水三氟甲基对pH响应性表面基团的可切换性能的影响，（iii）通过使用施加的电势改变局部pH值来主动控制这些膜和界面的响应的能力。在这些目标内，本论文的工作将确定薄膜厚度和均匀性对水渗透速率和机理的影响，并指导薄膜的生长，放大表面性质中pH或电位驱动转化的幅度的特征。 结合起来，这些目标将确定薄膜组合物，放大薄膜的表面和阻隔性能的响应，并将开发新的方法，积极控制薄膜的性能。更广泛的影响所产生的拟议活动该项目将整合研究和教育，为本科生，特别是少数民族学生，获得智能薄膜/界面的研究经验，并通过开发新的学习材料，在五个不同的课程，从新生到研究生水平。该项目包括动力学，传质和分子设计方面，将纳入讲座作为案例研究，例子和家庭作业问题，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学金，在三个夏天内资助三名本科生。通过他们的工作，本科生将实施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，学生将发展增强的分子直觉，并将获得对科学过程的深刻理解。

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.