Dynamics of Multicomponent Polymer Liquids

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This research is directed at the development and application of methods in optical rheometry to measure the dynamics and structures of multicomponent polymer liquids when subjected to processing conditions. Such liquids are characterized by dynamics associated with specific structural constituents that should be separated to properly understand the response of these materials to external fields. This separation can refer to the isolation of the dynamics as a function of length scales existing in the liquid, or associated with specific chemical components. The former class of systems would include phase-separated blends where the response of the domain structure must be isolated. Scattering techniques are the obvious choices for these cases and for structural length scales in the range of 0.5 to 20 um, small-angle light scattering and scattering dichroism will be used for this purpose. Spectroscopic techniques are required when the dynamics of individual chemical elements must be identified. Infrared polarimetry and Raman scattering will be developed and applied to single-phase polymer blends and melts. The specific tasks that will be carried out are: 1.) For miscible, single-phase blends, it is important to understand the composition and temperature dependence of the friction factors of the individual components. An additional piece of information that is required is the entanglement molecular weight as a function of composition. To address these goals, infrared dichroism and a new technique, polarization modulated Raman scattering, will be used to spectroscopically identify specific chemical constituents. 2.) In systems where shear can affect the phase behavior of a multicomponent system, both scattering and spectroscopic techniques will be used to examine the structure over a wide range of structural length scales. For systems with a dispersed phase, small-angle light scattering will be used to monitor the deformation of those droplets. This will be carried out for systems where the viscosity ratio of the components making up the mixtures is varied. To examine the interactions that drive miscibility or phase separation, a new technique, two-dimensional Raman scattering will be developed. This method will offer the capability of measuring orientation correlations between distinct elements comprising a sample. Finally, excimer fluorescence will be developed as a technique to probe interactions over extremely small (10 angstrom) length scales. This research is jointly supported by the Polymers Program in the Division of Materials Research and the Fluid, Particulate and Hydraulic Systems Program in the Division of Chemical and Thermal Systems.