Spatial gradients in dynamics of near-interface polymers: Experiments and theory

NON-TECHNICAL SUMMARY

Near-interface polymers or interfacial polymers refer to polymers at the nanometer vicinity of a boundary between two phases or two components. The dynamics and mechanics of near-interface polymers can have strong implications for the design and performance of various nanostructured polymeric materials, polymer nanocomposites, thin polymer films, and functional interfaces which have numerous applications in areas such as energy, environmental, healthcare, infrastructure, and sustainability.

For instance, thin polymer film design plays an essential role in the multi-billion dollar semiconductor industry. In many instances, the polymers at the nanometer vicinity of interfaces can exhibit large spatial variations (sometimes orders of magnitude) in elastic moduli, viscosity, and diffusion coefficient. A fundamental issue that this project will address is the molecular mechanisms responsible for these large variations and the spatial dependence of the near-interface polymer dynamics.

By improving our understanding of these microscopic effects, this project will allow for the rational design of polymers at the interface. This project will also offer training for graduate students with multiple characterization tools, including spectroscopy, rheology, and small-angle scattering, and will provide opportunities for them to use national user facilities and build a network of professional contacts.

Furthermore, the project expands research participation by engaging undergraduate students, with recruiting emphasis on students from underrepresented groups through the Lansing School District (74% population are African American) and the Lansing Community College/Michigan State University 2+2+2 Engineering Program. An educational program on polymers at the interfaces will also be implemented at the graduate level.

A K-12 outreach-activities module will be created and delivered through MSU K-12 high-school summer camp to improve public understanding of polymers and polymers at the interface. TECHNICAL SUMMARY

This project aims to elucidate the dynamics gradients of near-interface polymers and their dependence on polymer chemistry and nanoconfinement. Polymers at the interface can exhibit profound alterations in dynamics and mechanical properties compared with the bulk. These changes can involve large shifts (> 50 K) in glass transition that correspond to six to eight decades of change in structural relaxation time.

However, deficiencies in the quantification of gradients of interfacial dynamics impose grand challenges and obfuscate the understanding of interfacial dynamics and their connection with the bulk glass transition. A comprehensive experimental program will quantify the dynamics gradients at the interface through a combination of dielectric spectroscopy, rheology, and small-angle scattering.

A new dielectric marker system will be developed with their precise placement at the interface to quantify the dynamics of the near-interface polymer at ~ 1 nm spatial resolution. With this new development, the PI’s group will further quantify the exact function forms of the interfacial dynamics gradient and the effects of polymer chemistry and nanoconfinement on the interfacial dynamics gradients.

These experimental results will provide critical tests of existing theoretical models, and help to formulate a qualitative description of the interfacial effect and nanoconfinement effect for near-interface polymer dynamics.

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.