Interfacial Behavior of Stimuli-Responsive Multicomponent Molecular Bottlebrush Polymers

PART 1: NON-TECHNICAL SUMMARY Bottlebrush polymers are large chain-like organic molecules comprising a long polymer backbone decorated with densely grafted shorter polymer side chains, resembling the brushes for bottles and pipes as well as bottlebrush flowers. These polymers have shown promise in numerous applications, from optical films for modulating the color of light to delivery of drug molecules for medication, advanced materials with unusually soft mechanical properties for protection of fragile objects, and biomimetic lubricants for friction reduction. Stimuli-responsive multicomponent bottlebrush polymers contain two or more chemically distinct side-chain polymers with at least one exhibiting a tunable solubility in water that can be readily modified by external stimuli, such as a temperature change or light. These polymers can change their ways of interacting with the environment according to external conditions, displaying an adaptive behavior. In this project, stimuli-responsive multicomponent bottlebrush polymers will be made, and their mechanical and responsive properties at water-oil interfaces will be studied. The knowledge gained from this research could impact many technologies, in particular, stimuli-responsive emulsions, which are of tremendous interest to enhanced oil recovery and medicine. The project will provide a platform for training graduate and undergraduate students, contributing to the nation’s science and technology workforce development. The PI will host and mentor high school students at the University of Tennessee Knoxville to stimulate their interest in STEM fields and broaden their horizons. PART 2: TECHNICAL SUMMARY This project is aimed at achieving stimuli-responsive multicomponent molecular bottlebrush polymers that exhibit solid-like characteristics when adsorbed at liquid-liquid interfaces and fast kinetics of desorption from interfaces when triggered by external stimuli. Specifically, the project seeks to design and synthesize stimuli-responsive multicomponent bottlebrush polymers with various architectures and compositions, investigate their properties and behaviors at water-oil interfaces, and identify critical molecular parameters that give rise to elastic interfacial behavior while exhibiting fast desorption from liquid-liquid interfaces in response to external stimuli. A series of multicomponent bottlebrush polymers with systematically changed backbone and side-chain lengths, different arrangements of side-chain polymers, and various grafting densities will be prepared using the well-established state-of-the-art synthesis techniques. The interfacial activities and responsive properties of these brush polymers will be studied by emulsification experiments and pendant drop tensiometry, and the mechanical properties of bottlebrush polymer films adsorbed at water-oil interfaces will be characterized by interfacial rheological measurements. The effects of various molecular parameters on the mechanical and responsive properties of these bottlebrush polymers will be elucidated. The fundamental understanding obtained from this research project could pave the way for developing a new class of interfacial stabilizers for applications in stimuli-responsive emulsions and emerging technologies. . 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.