The 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 Merit
The 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 Activity
The 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.
