Correlated Many-Chain Dynamics: Slow Modes, Entanglements, and Glass Transition.

点击翻译按钮获取中文摘要

9971687 Guenza A key to understanding the technological and biological properties of polymeric materials is to have a powerful theoretical approach that is capable of making the connection between molecular structure and experimental data. A molecular level understanding of the macroscopic properties of polymeric systems is essential for a successful tailored synthesis of new materials with specific properties. Several rigorous theoretical approaches have been developed that successfully describe the experimental findings on the basis of a microscopic physical picture. However, since the range of temporal and spatial scales of the important motions in polymeric fluids is so broad (from psec to days, years or even longer), in the past different approaches have been developed that are specific for each physical phenomenon. For some important phenomena, a theory has not yet been developed, as in the case of the dynamics of supercooled polymer systems.To have a consistent treatment of the physics of polymers we need to have a theory that can describe, in a unified way, polymer systems in different environments: at different temperatures (from the melt to the glass transition), different polymer volume fractions (from single molecule solution to melt), different architectures (linear, star, dendrimers), and different local polymer flexibilities (protein, DNA, polymer liquid srystals). While the importance of a unified theory has always been clear in principle, it has never been possible to achieve this goal until now.A new theoretical approach is developed and applied for a unified picture of the dynamics of polymeric systems. The key ingredient is the presence of contributions describing not only the intramolecular, but also the intermolecular interaction terms in the dynamic equations. For weak intermolecular interactions, the theory recovers the single chain dynamics as described by the Rouse theory with memory function, i.e., the generalized Langevin equation. Increasing the strength of the intermolecular interactions, the theory describes the simultaneous dynamics of many chains characteristic of a polymeric liquid. For very strong intermolecular interactions anomalous exponents appear in the polymer diffusion and time correlation functions. Interestingly, the strength of the potential can be enhanced in different ways: by increasing the molecular weight of the polymer, by increasing the polymer volume fraction, or by decreasing the temperature of the system. The same equations describe the anomalous dynamics that appear in entangled polymer fluids, supercooled polymer systems, and highly dense polymer fluids.%%%A key to understanding the technological and biological properties of polymeric materials is to have a powerful theoretical approach that is capable of making the connection between molecular structure and experimental data. A molecular level understanding of the macroscopic properties of polymeric systems is essential for a successful tailored synthesis of new materials with specific properties. Several rigorous theoretical approaches have been developed that successfully describe the experimental findings on the basis of a microscopic physical picture. However, since the range of temporal and spatial scales of the important motions in polymeric fluids is so broad (from psec to days, years or even longer), in the past different approaches have been developed that are specific for each physical phenomenon. For some important phenomena, a theory has not yet been developed, as in the case of the dynamics of supercooled polymer systemsIn this grant a new theory will be developed which provides a unified approach to diverse phenomena in polymers. Besides increasing our fundamental understanding of these systems, this work will also have technological applications.