Frank M Tiller Professor in the William A. Brookshire Department of Chemical and Biomolecular Engineering Jacinta Conrad, PI, has received $259,749 in NSF funding for her proposal, Collaborative Research: Effect of Polymer Chemistry on Penetrant Transport in Weak Polyelectrolyte Brushes, with Co-PI and Ernest J and Barbara M Henley Professor Jeremy Palmer. This project is a collaboration with Rice University’s Amanda Marciel, who received a further $290,251 for her part of the project.
They’re interested in studying what are called polymer brushes: polymer chains, or long repeating units tethered to one end of a surface, which can modify the properties of a given surface. For example, these chains might make a surface softer or change its charge. Conrad and Palmer are particularly interested in brushes whose properties change in response to environmental conditions.
Many applications in filtration and membrane separation involve surfaces through which fluids, ions, or small particles must be able to move. Better understanding how these changes in surface properties change the way that penetrants are able to transport is a large and open-ended goal, but that’s not unexpected for Conrad’s group. Rather than centering direct applications, they often focus on projects that allow them to investigate precisely this type of broad, fundamental question.
“In this proposal, what we’re specifically looking at is how much hydrophobicity matters,” said Conrad. “We’ll change the hydrophobicity of the monomers that make up the polymers in the brushes. Many of the desirable properties of charged polymer brushes are thought to arise from how they interact with water — and, particularly, how much they like it — but how hydrophobicity affects brush conformation and response remains incompletely understood.”
“Prior work in this area has shown that there are fundamental knowledge gaps regarding how polymer chemistry influences chain conformations in polymer brushes under various environmental conditions,” Palmer said. “Our group’s contribution will be to perform complementary computational modeling of these systems to help predict how polymer chemistry influences the stimuli-response behavior of brushes.”
“We proposed several hypotheses that we will test in this project, but our overarching goal is to advance knowledge and gain better understanding of the stimulus response of polymer brushes. How the monomer composition changes the stimulus response is important for the practical design and use of these systems,” added Conrad.
They hope to experimentally quantify these behaviors: how the brush conformation changes and how that alters bulk properties such as the contact angle of water on the brush surface.
“The polymer brushes we’re interested in are known as stimulus-responsive — they change their conformation in response to solution conditions. For example, we add salts, or we change the pH, or we change the temperature, and they change their conformation. This is interesting from an application standpoint because these brushes can be used to make switchable surfaces: the brush has one conformation at one temperature, and then I apply a stimulus, and it changes its conformation and its properties,” she added.
“As an example, polymer brushes can be used to create self-cleaning surfaces. Foulants that absorb on the surfaces can be removed by changing the solution pH or salt concentration to elicit a conformational change in the polymer chains; the conformational changes help to mechanically expel the foulants from the surface,” added Palmer.
“This project excites us because none of the current theories correctly predict their behavior, and we want to try to understand why. We hope that our experiments and simulations can inspire other researchers to develop theories that better predict the brush conformation and its surface properties as we change the composition of the monomers that make up the brush. As one example of how this might be useful, it may be possible to control membrane surface properties by synthesizing brushes using specific monomers at specific ratios. We’re not going to do that ourselves, but we hope to enable people to do that by developing this knowledge base.”
This collaborative, stepwise approach also influences her overall mindset regarding project funding.
“The kinds of projects that NSF supports are essential for training our graduate students and building the scientific workforce,” said Conrad. “Threats to federal funding limit our ability to do that. Every time we get a new grant, we are able to train one or two or several more students. Recognizing that there is this direct connection between federal support and not just the discoveries, but also the ability to train the people who are going to go off and be the broad part of our scientific workforce, is so important.”