CAREER: Evaluating Theories of Polymer Crystallization by Directly Calculating the Nucleation Barrier in a Polymer Melt

NONTECHNICAL SUMMARY

Polymers are long-chain molecules found in a wide array of natural and man-made materials, ranging from DNA, wood, and rubber to piping, clothing, and grocery bags. Many essential polymer materials have a structure that is at least partially crystalline, meaning the atoms within the molecule arrange themselves regularly in space. Crystallinity plays a crucial role in determining the properties of polymer materials, and thus it is critical that scientists and engineers be able to understand and manipulate how and when polymers crystallize.

Despite extensive research, the exact mechanism behind polymers crystallization remains unknown. There are several competing theories, but evidence from experiments and computer simulations has been inconclusive. This project will apply a simulation method that was successfully used to study the crystallization of non-polymers such as water to study polymers.

The project objectives will focus on studying how the length of the molecules and the different types of polymers affect the mechanism of crystallization. Success with this new approach could revolutionize our basic understanding of how polymers form crystals, potentially leading to the development of innovative new materials and reduced environmental impacts from existing ones.

The project will also include educational objectives that are integrated with research activities. Specifically, the project will create mentoring opportunities between undergraduates and K-12 students, between the PI and undergraduates, between more and less experienced graduate students, and between the PI and future scientists through the creation of a podcast that focuses on career development in the sciences.

TECHNICAL SUMMARY

Despite decades of research, polymer science lacks a widely accepted theory for crystallization from the melt state. The development of an accurate theory of polymer crystallization would not only change textbooks, but it would also enable the creation of new polymers with better properties and processes for making polymers with less environmental impact.

Nucleation processes are foundational to polymer crystallization, but accumulating evidence suggests that Classical Nucleation Theory inadequately explains homogeneous nucleation, leading researchers to propose controversial alternative theories. The central hypothesis of this project is that equilibrium advanced sampling methods can be used to directly calculate the nucleation barrier to test these new theories.

While new to polymer crystallization, advanced sampling methods have been used study nucleation in other fields, and they have distinct advantages over other methods. Accordingly, this project will focus on a study of the nucleation barrier for folded-chain crystals as a function of polymer molecular weight and as a function of polymer chemistry. This project will also contribute to the ongoing development of simulation software for computing free energy landscapes in low-temperature polymer melts.

The project will also involve integrated research and teaching aims specifically focusing on effective and scalable mentoring opportunities for students spanning from K-12 through graduate education levels. Mentoring new scientists and engineers, especially underrepresented minorities, is a key educational component of cultivating a globally competitive and diverse workforce.

Specific mentoring activities include near-peer mentoring and outreach to K-12 students, PI-mentored undergraduate research, scalable mentoring experiences through the production and distribution of the podcast ``How Science Happens,'' and near-peer mentoring of graduate students through a chemical engineering student council.

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.