The objective of this NSF project is to exploit the interface sensitivity of infrared-visible sum frequency generation spectroscopy (SFG) to measure acid-base interactions at solid-solid interfaces. An understanding of polar interactions is important in the areas of adhesion, friction, and wetting. In-situ characterization of acid-base interactions and their role in adhesion of these coatings at the molecular level and under kinetic conditions (for example: during sliding and mechanical contact) pose a formidable challenge to scientists. The principal investigator (PI), Professor Dhinojwala, proposes to directly probe the acid-base interactions for polymers in contact with inorganic sapphire substrate or sapphire modified with self-assembled monolayers with acidic or basic end groups to understand these interactions at the molecular level. SFG instrumentation is used to directly monitor the shifts in the vibrational peaks of the acidic and basic groups and correlate them with interaction energies to study exchange kinetics at polymer-solid interface as a function of time, temperature, and composition. This proposal explores the kinetics and thermodynamics of surface segregation driven by acid-base interactions. In addition, this proposal focuses on blends and copolymers to study the role of these interaction energies on the segregation of near solid-solid interfaces and dynamics during sliding and peel-off. The study of interaction energies and its experimental results have important implications in understanding friction and adhesion hysteresis. These interaction energies will be compared with adhesion measurements using the Johnson-Kendall- Roberts (JKR) geometry. In addition to these experiments, the PI will also conduct atomistic molecular dynamics simulations (MD) and quantum calculations to understand the magnitude of the frequency shift and its effect on segregation. The SFG, MD, and quantum calculations of these experiments will be used in conjunction to understand the influence of surface concentration, steric constraints, and surface roughness on acid-base interactions and the consequences on adhesion energies.
The fundamental understanding of acid-base interactions helps in predicting the adhesion of polymers to substrates and in developing the next generation of enhanced coatings and adhesives for applications in multiple areas, including, but not limited to, electronics, bio-mineralization, peptide-based surface recognition, nano-composites and solar cells. This project will support two graduate students who will work together as a group with experts in the areas of surface science, MD simulations, and industrial research. The students working with this broad multidisciplinary group will be provided training to work as a team. Additionally, the graduate students will also have the opportunity to supervise NSF-REU students during the summer. As a volunteer Director of District 5 Science Day, the PI will continue his outreach to host District Science Day at The University of Akron (UA). The PI has also initiated a mentorship program where he brings together scientists from industries and academia to mentor the science projects. This mentorship program was started in the city of Hudson, Ohio, and the PI plans to make this program available to all schools in District 5. In collaboration with UA's business school and Austen Bio-innovation Institute in Akron, the PI is helpping in developing a multidisciplinary Bio-design class offered to UA students in physical sciences, business, and medicine with a goal of observation or experimental based approach to solve problems. This class will be taught in collaboration with professors from UA's business and medicine schools.