Investigating Small-Scale Effects on Dynamic Properties of Polymers

University Of Akron, Akron OH

Investigators

Abstract

0103704 Leuttmer-Strathmann Understanding the relationship between the structure of polymer chains and the properties of polymeric materials has been a long-standing goal of polymer science. A case in point are the transport properties of polymers in the liquid state (viscosity, thermal conductivity, diffusion coefficients) which are important in polymer processing and applications, but cannot typically be predicted from the structure of the constituents and the thermodynamic state of the system. The purpose of this theoretical research grant is to add to our understanding of the structure-property relationship by investigating small-scale effects on the dynamic properties of polymeric fluids. Local chain structure and environment affect dynamic properties as different as viscoelasticity and thermodiffusion. They do so most strongly in concentrated systems like polymer melts and blends, but even in dilute solutions, signatures of the local structure can be detected. This grant focuses on three aspects of this large area: the first two relate to the friction experienced by chain segments while the third addresses heat transfer between chain segments. The three parts of this project are steps toward a consistent description of small-scale effects for all dynamic properties of polymeric fluids. Furthermore, all three contribute towards a prediction of these effects from the structure of the molecules and the thermodynamic state. Both local chain structure and local environment affect the mobility of polymer chains in blends and melts. In this project, local effects on polymer dynamics will be investigated through a small-scale simulation approach. Expressed as local friction coefficients, the simulation results can be combined with coarse-grained theoretical models to make predictions about viscoelastic and diffusion coefficients. Several polymer systems will be investigated in detail in this work and predictions for their dynamics compared with experimental data. Experiments on a large number of miscible polymer blends have shown that blends display complex dynamic behavior resulting from differences in the local environment of the chain segments. The nature of the local heterogeneities, however, is still under discussion and different models for local environments have been proposed. In order to investigate this problem, small-scale simulations will be evaluated based on different models for local heterogeneity and the resulting predictions for dynamic properties of miscible blends will be compared with experimental data. The transport of thermal energy through a dense polymeric fluid is not well understood and often treated independently from other dynamic processes. The work proposed here extends a microscopic lattice network model for heat transport through polymer melts in order to investigate heat transfer between segments on different chains. The results will enable us to develop a coarse-grained lattice model for dynamic properties that incorporates both chain mobility and heat conduction in dense polymeric fluids. %%% Understanding the relationship between the structure of polymer chains and the properties of polymeric materials has been a long-standing goal of polymer science. A case in point are the transport properties of polymers in the liquid state (viscosity, thermal conductivity, diffusion coefficients) which are important in polymer processing and applications, but cannot typically be predicted from the structure of the constituents and the thermodynamic state of the system. The purpose of this theoretical research grant is to add to our understanding of the structure-property relationship by investigating small-scale effects on the dynamic properties of polymeric fluids. ***