Structural Recovery and Physical Aging in Plasticizing Environments

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The discovery of anomalous volume recovery in polymer glasses subjected to plasticizer-jumps through the glass transition will be explored using three new classes of experiment. First, the kinetics of mass absorption during structural recovery will be investigated. Second, the first enthalpy recovery experiments after plasticizer-jumps will be performed to determine if the observed volume anomalies are also found in the enthalpy part of the glassy structure. This will require development of a unique pressure cell for the Calvet calorimeter in the laboratories of the PI. Third, a non-resonant dielectric hole burning spectroscopy (NSHB) technique will be developed to establish how dynamic heterogeneity of the plasticizer-jump and T-jump created glasses compares. The experimental results will be interpreted within the energy landscape paradigm for glass-forming materials. The work will provide the first complete set of data that constructs the full range of macroscopic variables (volume, enthalpy and concentration) and relates them to a measure of the microscopic nature of the material (NSHB) during the evolution of glassy structure or physical aging. Finally, the development of the NSHB capabilities at Texas Tech University will be the first such apparatus in the United States.%%%The graduate students and post-doctoral researcher will perform the proposed research under the direct supervision of the PI. The proposed work is expected to provide excellent training for the graduate student and post-doctoral associate in cutting edge research. As part of their training, the graduate student and post-doc will attend and present their research results at national or regional meetings. In addition to providing good training for students, the results of the project will be incorporated to the extent feasible in both undergraduate and graduate courses taught by the PI. Because the research is interdisciplinary, containing multiple aspects of polymer materials science (structural recovery and plasticization of glass forming materials) and calorimetry as well as fundamental condensed matter physics (non-resonant spectral hole burning) the work provides a rare educational opportunity for the graduate student and post-doc. They will be expected to be familiar with all aspects of the program. In addition, the work involves two significant instrument design and construction tasks (pressure vessel for calorimeter and dielectric NSHB apparatus) that are important in the education of experimental scientists. ***