Development of Molecular Simulation Techniques for Probing Solvent Effects in Polymer Films during Solvent Vapor Annealing

University Of Delaware, Newark DE

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports computational and theoretical research to simulate a method to fabricate films made of polymers - long chain like molecular assemblies with repeating molecular units. Polymers are used universally in every-day materials, such as automobile parts, plastic cups, and food packaging, and in high technological applications, such as microelectronics and solar cells. The properties of polymer-based materials can be optimized for a given application by tuning the arrangement of constituent molecular units. This motivates materials scientists in industry and research labs to find processing techniques that will enable precise control over the molecular arrangement within the polymer materials. One such processing technique is solvent vapor annealing, where the polymer film is exposed to a solvent vapor so that the solvent molecules mix in with the polymer film which alters the polymer-polymer interactions and leads to a particular resulting arrangement. This method has allowed materials scientists to obtain polymer arrangements that have not been possible to achieve before, thus paving a pathway for creating next generation of materials. Despite the proven value of this technique, optimized universal protocols have not been established due to a lack of fundamental knowledge about this technique. In this project, the PI will develop models and computer simulation approaches to gain fundamental understanding, advance predictive modeling, and make solvent vapor annealing a universal, practical, and reliable method facilitating the engineering of polymers for various technologically relevant applications, such as fuel cells, photovoltaics, and nanomembranes. The PI will also dedicate significant effort to undergraduate education, specifically through training and mentoring of undergraduate students in her research lab as well as in the classroom through her Introduction to Polymer Science and Engineering course. In her role as organizer of many national conferences in the area of polymers she plans to invite leading women computational soft materials scientists from around the country, facilitating the dissemination of polymer science research, as well as serving to inspire future generation of women scientists and leaders. TECHNICAL SUMMARY Solvent vapor annealing is an increasingly utilized polymer processing method where the presence of solvent within the polymer film enhances the mobility of the polymers, alters the effective polymer-polymer and polymer-surface interactions, and drives morphological changes. Through solvent vapor annealing and eventual instantaneous solvent evaporation, some technologically useful morphologies that are not seen at equilibrium can be trapped. Despite the proven value of this processing technique, especially in block copolymer films, standardized or universal protocols have not been established due to a lack of fundamental knowledge regarding the complex interplay between solvents, substrate, and polymer(s) during solvent annealing and solvent evaporation. This lack of knowledge is due in part to a) the limitations in experimental techniques for probing these solvent-polymer interactions and solvent mediated polymer-polymer interactions in situ, and because b) in most computational studies of polymers the solvent is treated implicitly or when treated explicitly the solvent and polymer dynamics during solvent vapor annealing are not captured. To address this lack of fundamental knowing the overarching goal of this project is to develop new computational approaches to simulate solvent vapor annealing in polymer films. The computational research will uncover the thermodynamics and kinetics underlying solvent-induced morphology changes within polymer thin films and provide universal guidelines on the use of solvent vapor annealing to achieve target morphologies in homopolymer blends and conjugated polymer based films. Through comparison with data from experiments these computational techniques will be validated and provide guidance on the selection of solvent chemistries and solvent vapor annealing conditions for achieving desired target solvent-induced effects in the polymer film. Such a fundamental understanding will be valuable for solvent vapor deposition to become a universal, practical, and reliable method facilitating the design of polymer and other soft materials films used in various technologically relevant applications, such as lithography, fuel cells, photovoltaics, and nanomembranes. The computational tools developed in this project will be made available for others studying systems beyond homopolymer blends and conjugated polymers, such as polymer nanocomposites and block copolymers. The PI is also committed to achieving excellence in education and outreach efforts. She will dedicate significant effort to undergraduate education, specifically via training and mentoring of undergraduate students during their contributions towards the proposed work. The results and tools pertinent to the proposed work will also be included in an Introduction to Polymer Science and Engineering course that she teaches in the fall to undergraduates and graduate students from chemical engineering and materials science. The PI will continue her extensive past efforts to recruit and retain female students and mentor them to leadership roles in industry, universities, and national laboratories. Through her role as organizer of various national conference, the PI aims to invite leading women computational soft materials scientists from around the country, facilitating the dissemination of outstanding work, as well as serving to inspire future generations of women scientists and leaders.