This award supports theoretical research and education with an aim to develop theories of polymer crystallization and directed polymer assembly, by employing simulation techniques and statistical mechanics. Crystallization of polymers from solutions and melts is one of the longstanding research areas in polymer science. A fundamental understanding of how polymer chains organize into hierarchical structures remains elusive. The conformational entropy of flexible polymer molecules makes the crystallization phenomenon of polymers distinct from ordering of small molecular systems. The same entropic aspects of polymers are manifest in various directed assemblies of diblock copolymers and biological polymers. Previous work by the PI to address the effects of the conformational entropy has resulted in novel ways of interpreting the rich phenomenology of polymer crystallization. These are complementary to the traditional arguments in the literature, which essentially ignore the conformational entropy. This award supports research that will build on recent new ideas to explore several related ordering phenomena of polymers. Specifically, (a) lamellar morphology in polymeric spherulites, (b) kinetics of growth fronts in polymer solutions and melts, and (c) directed assembly of polymers will be addressed. This project is aimed at building new conceptual models and discovering new laws of polymer assembly. The proposed theoretical work complements experimental investigations being actively pursued in laboratories worldwide.

NON-TECHNICAL SUMMARY

This award supports integrated computational and theoretical research and education aimed to understand how, polymers, large long-chain molecules made of many smaller repeating molecular units, organize into ordered states. Of particular interest is how they crystallize. The many ways long-chain molecules can twist and bend makes the crystallization process of polymers distinct from that of many other materials. The PI will use computer simulations and build on previous work, his own and that of others, to develop an understanding of polymer crystallization.

The results of this research may have impact in numerous applied areas such as polymer processing, the fabrication of polymeric materials down to scales some ten thousand times smaller than a human hair, and the process by which molecules and other 'building blocks' of materials assemble themselves to form biological structures and living matter. Many, if not most, modern materials are made from processed semicrystalline polymers, which are the subjects of the proposed theoretical and modeling investigation. A fundamental understanding of the behavior of this important class of materials will help to design and process novel polymeric materials with enhanced benefits to our society. This activity provides support for training of graduate students in this challenging research area and the workforce of the twenty first century.

Project Report

One of the outstanding phenomena in polymer science is the ability of a collection of interpenetrating and entangled long flexible polymer chains to organize into crystals. The fact that the chains are intermingled among themselves is responsible for the crystallization process being heavily frustrated. We have developed a modern theory of how such intermingling long chains form crystals. This theory of growth kinetics considers the presence of a boundary layer with an entropic barrier, at the growth front, arising from conformational frustration associated with jamming of chains at the growth front. Our theory gives the correct crossover description between the high molecular weight and low molecular weight limits of growth rates of lamellae. Examples of investigated polyemr crystallization processes include semicrystallinity in polyolefins, formation of gigantic chiral morphologies in polymer crystals, virus assembly, formation of S-layers in bacteria, DNA ejection from viruses, clathrin basket formation, and wrapping of objects by membranes. The research area of polymer crystallization is at the core of a multi-billion dollar industry and our work is of high impact in terms of predicting the desired experimental conditions to improve polymer properties. Also, contribution to education at all levels (K-12, high school, undergraduate, graduate, and postdoctoral) has been an essential part.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Application #
1105029
Program Officer
Daryl W. Hess
Project Start
Project End
Budget Start
2011-09-01
Budget End
2014-08-31
Support Year
Fiscal Year
2011
Total Cost
$300,000
Indirect Cost
Name
University of Massachusetts Amherst
Department
Type
DUNS #
City
Amherst
State
MA
Country
United States
Zip Code
01003