Organic polymeric materials, or plastics, break down due to the mechanical forces they experience during their use cycles. The mechanical degradation of polymers limits their use in lightweight structural materials, consumer products, and biomedical applications. Prof. Stephen Craig at Duke University is learning how to dictate the rates and outcomes of chemical reactions that are accelerated by an applied mechanical force. These reactions impact multiple aspects of materials design, including the macroscopic failure and mechanical limitations of current polymeric materials. In addition, mechanically responsive functional groups might serve as the critical elements in new stress-responsive and self-healing polymeric materials. Prof. Craig's studies aim to provide insight into how the macroscopic mechanical forces experienced by polymers during use can be effectively channeled into desired chemical responses, providing a foundation for new classes of polymers. Broader impacts of the project include: (1) integration of research and education through a new, regional technical training program that supports and enriches the research activities and scientific training experiences provided by primarily undergraduate institutions, community colleges, advanced high schools, and smaller research universities; (2) active learning modules and associated laboratory experiences in introductory chemistry and through coupled undergraduate and high school research experiences; (3) broadening the participation of underrepresented groups by engaging and recruiting young scientists early in their scientific careers, before the onset of disproportionate attrition from the sciences; (4) disseminating the results of the research broadly; and, (5) addressing fundamental questions of molecular behavior in materials in a manner that will have an impact on a broad range of fields including polymer chemistry, physical organic chemistry, and self-healing and stress-responsive materials.

The overarching technical objective is to lay a quantitative foundation for mechanochemical kinetics by employing state-of-the-art physical measurements and developing new methods for quantitation. Specific experiments include the direct, experimental characterization and quantification of the effect of mechanical forces on covalent reactions triggered along overstretched polymer backbones. Because mechanical force, unlike conventional forms of energy input such as heat or light, is directional, the coupling between mechanical force and reactivity provides insights into the structure of transition states and the shapes of reaction potential energy surfaces. Despite its importance, however, quantitative measures of the effect of force on chemical reactions are rare. This project aims to develop two novel approaches to quantifying mechanochemical reactivity: pulling on single molecules of multi-mechanophore, non-scissile polymers with an atomic force microscope, and the pulsed sonication and molecular weight degradation of multi-mechanophore, scissile polymers. Models for the observed mechanochemical activity enable quantitative assessment of reactivity in both classes of mechanophores.

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.

Agency
National Science Foundation (NSF)
Institute
Division of Chemistry (CHE)
Type
Standard Grant (Standard)
Application #
1808518
Program Officer
Suk-Wah Tam-Chang
Project Start
Project End
Budget Start
2018-08-15
Budget End
2023-07-31
Support Year
Fiscal Year
2018
Total Cost
$926,000
Indirect Cost
Name
Duke University
Department
Type
DUNS #
City
Durham
State
NC
Country
United States
Zip Code
27705