Theory of polymer crystallization, melting, and interlude of metastability

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research, and education to advance understanding of polymer crystallization. Very long and thin chain-like gigantic macromolecules make up the class of materials, called polymers. These materials have redefined our contemporary civilization, through clothing, building materials, automobile, and aircraft parts, and much more. One of the key features required in polymeric materials so that they will be useful as end-products with market value, is the ability to make crystals from them. But this macromolecular process must be an impossible task as can be easily envisaged by considering a large number of long and intermingled wires which are all tangled up. How can they organize neatly into crystals? In fact, the molecules do indeed form crystals, at least partially. In spite of the prevalence of such partially ordered polymeric crystals in the multi-billion-dollar industry of polymers, this process is not understood. A molecular understanding of the crystallization process of polymeric materials is one of the longstanding research challenges in the world of materials. The multitude of puzzles collected phenomenologically over many decades in this field demands a rational conceptual foundation, which will facilitate discoveries of new materials in addition to understanding the known facts. This research program is aimed to develop fundamental concepts to understand how polymers crystallize and melt, using theory and computer modelling. In addition to advancing the field of polymer crystallization, the proposed activities include strong support of diversity and training a new generation of graduate students enabling their future participation in the multi-billion-dollar industry of semicrystalline polymers. TECHNICAL SUMMARY This award supports theoretical and computational research, and education to advance understanding of polymer crystallization. Crystallization of polymers from solutions and melts is one of the longstanding research areas in polymer science with tremendous industrial value. Due to enormous number of conformations that can be taken up by flexible macromolecules, their crystallization and melting behaviors exhibit a broad range of puzzling phenomenology which has been challenging to understand. These puzzles emerge from rich structural hierarchies at multiple length scales and time scales often involving long-lived non-equilibrium states. This research program is aimed to develop new theories of polymer crystallization, melting, and the interlude of hierarchy of metastable states. Building on new insights into the role of long-lived metastable states and memory effects in semicrystalline polymers, the proposed research will be performed using statistical mechanics, field theory, and several simulation techniques. Specifically, the PI plans to address: (i) interlude of metastable states in crystallization, melting, and memory, (ii) vertical crystallization by lamellar stacking, (iii) spontaneous selection and amplification of chirality, and (iv) instability of interlamellar amorphous regions. The results from the research program are expected to have significant impact in numerous industrially relevant areas such as polymer processing. Most of the materials today are made from processed semicrystalline polymers, which form the focus of the proposed work. These materials constitute a multi-billion-dollar industry. A fundamental understanding of this important class of materials will help to design and process novel polymeric materials with enhanced benefits to our society. Training of graduate students and postdoctoral researchers in this challenging research area is a strong educational component of the research program. 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.