Star-Shaped and Linear Polymers in Temperature-Responsive Layer-by-Layer Assemblies
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PART I: NON-TECHNICAL SUMMARYFunctional 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.
