This award supports integrated research, education and outreach activities in theoretical polymer physics. This research activity is aimed of developing a new theory of polymer crystallization, by employing several simulation techniques and statistical mechanics. Crystallization of polymers from solutions and melts is one of the longstanding research problems in polymer science, full of intrigue and in need of unifying conceptual themes. A fundamental understanding of how polymer chains organize into hierarchical structures is still elusive. This work builds new conceptual models and discovers new laws of polymer assembly. This theoretical effort complements many experimental investigations being actively pursued in many laboratories worldwide. The results are also relevant to numerous applied areas such as polymer processing, fabrication of polymeric nanomaterials and biological self-assembly. The new theory is being used to understand several technologically important questions which include kinetics at the growth front, spontaneous selection of lamellar thickness and shape, flow effects, and the kinetics of melting.
Regarding the kinetics at the growth front, current classifications of lamellae in solutions and melts are divided into two groups that exhibit different temperature dependencies in the growth rates. Here, a model which depends upon polymer concentration and molecular weight is developed which unifies the growth rates of these two classifications. Specific focus is in applying this new model to determine the molecular details at the growth front at higher concentrations and for longer chains that has heretofore been possible.
In reference to spontaneous selection of lamellar thickness and shape, extensions of the calculations which assess the validity of the theory in certain experimentally interesting situations are underway. These include many-chain systems, explicitly accounting for chain stiffness, nearest-neighbor interactions, and inclusion of lateral- and fold- surface energies. This enables the exploration of the stability of any mesomorphic intermediate state.
To address flow effects the so-called shish-kebab configurations, identified from previous research of this investigator, are used as input for kinetic Monte-Carlo simulations. Starting from the shish and nucleated kebabs, the attachment of already folded chains from the solution onto the shish is simulated with full account of hundreds of thousands of chains. Also, to address the kinetics of melting of the lamella, Langevin-based dynamical simulations are being used. In particular the evolution and mechanisms which allow chains at the periphery of the lamella to exit the crystal are investigated. In addition to research, education of undergraduate, graduate and postdoctoral scientists is included in the research.
NON-TECHNICAL SUMMARY:
This award supports integrated research, education and outreach activities in theoretical polymer physics. The research seeks to understand how, polymers, large long-chain molecules made of many smaller repeating molecular units, organize into ordered states and is of central importance in many technologically relevant phenomena in materials science and biology.
Technologies impacted by polymers include rubbers, plastics, and fibers. This project addresses theoretical issues related to a very challenging question at the forefront of polymer research, namely: how do polymers crystallize? Extensive experimental efforts are also being mounted worldwide in this area and many challenging puzzles have emerged. A model based upon polymer concentration and weight is being developed which can determine growth rates as a function of temperature for two classes of polymers that are currently thought of as distinct. In addition to research, education of undergraduate, graduate and postdoctoral scientists is included in the research.
