CAREER: Understanding the Multi-Scale Dynamics of Heterogeneous Polymeric Systems

PART 1: NON-TECHNICAL SUMMARY:

Emerging polymer processing methods, such as 3D printing and imprint lithography, often require materials with unconventional rheological, or flow, properties. Such properties in liquid and solid states of polymers are dictated by the relationship between molecular motion on short length scales (about ten molecular bonds, ~1 nanometer) and molecular motion on long length scales (hundreds of molecular bonds, ~10 nanometers).

This project aims to understand these multi-scale polymer dynamics, leveraging tunable interactions between polymers and ultrasmall (~2 nanometers) nanoparticles as a model system. The fundamental understanding obtained in this study will guide materials designs to reveal unconventional flow properties. Moreover, newly developing fluorescence technologies will be employed to study multi-scale dynamics of polymer systems with high throughput.

This research is relevant in the polymer nanocomposites market, estimated to be $4.1 billion worldwide in 2019, and predicted to reach $8.5 billion by 2024. The educational plan is integrated with the research plan to inspire the next generation of planners, scientists, and engineers. The outreach and mentoring activities will broaden participation and will cultivate fascination and interest in polymers among K-12 students from low-income communities through demonstrations and laboratory internships.

A proposed new course for senior undergraduates and graduate students will bridge polymer/materials science to life sciences through cutting-edge fluorescence technologies with an emphasis on effective science communication. PART 2: TECHNICAL SUMMARY

The relationship between segmental and chain dynamics of polymers dictates both glass and melt properties and is crucial to designing processing operations. However, the physical foundations of this relationship across multiple time and length scales remain elusive despite much progress over the past sixty years, although it is clear that dynamic heterogeneities are the key contribution.

Attempts to understand the influence of heterogeneous segmental friction are limited by the difficulty to control spatial heterogeneity, and a lack of high-throughput experimental techniques for studying segmental and entire chain dynamics. To this end, this project aims to elucidate the influence of heterogeneous segmental friction on the decoupling of entire chain motion from segmental dynamics, i.e., deviations from the predicted relationships between segmental and entire chain motion for ideal homogenous polymers.

To establish a controlled heterogeneous system, the PI's group is developing polymer nanocomposites in which all chains are effectively interfacial with well dispersed, very small nanoparticles that are comparable in size to segments. Aims 1 and 2 will uncover the interplay of polymer-nanoparticle interactions and molecular weight on multi-scale dynamics.

In Aim 3, newly developing fluorescence technologies will be employed to study multi-scale dynamics of polymer systems efficiently. A comparison of experimental data to models such as the Heterogeneous Rouse Model will provide new insight into the decoupling of segmental entire chain motion in heterogeneous polymeric systems. It is anticipated that such decoupling will allow rheological properties to be altered simply by adding ultra-small nanoparticles or by designing polymers with optimal monomer sequences.

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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.