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Y. Meng and S. L. Simon, J. Polym. Sci: Part B: Polym. Phys., to appear, 2007.

Polymer Chain Length and Branching Effects on the Viscoelastic Bulk Modulus and Structural Recovery at High Pressure Sindee L. Simon, Texas Tech University, DMR 0606500.

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Y. Meng and S. L. Simon, J. Polym. Sci: Part B: Polym. Phys., to appear, 2007.

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  1. Polymer Chain Length and Branching Effects on the Viscoelastic Bulk Modulus and Structural Recovery at High PressureSindee L. Simon, Texas Tech University, DMR 0606500 The principal aim of this project is to measure the time-dependent bulk modulus K(t) as a function of polymeric architecture in polystyrenes in order to test Leaderman's hypothesis that the bulk modulus and shear modulus arise from different molecular mechanisms. The upper panel in Figure 1 to the right shows the bulk pressure relaxation master curves obtained at Po = 60.5 MPa (left-hand axis) and 30.2 MPa (right-hand axis) for Dylene 8 polystyrene.1Comparison of the pressure relaxation master curves and the shear creep compliance master curve measured by Agarwal2 and shown in the lower panel confirms that the bulk relaxation occurs primarily in the short time region of the shear response. It is concluded that the bulk and shear responses arise from similar molecular mechanisms at short times based on comparison of the responses and their shift factors, but that long time chain mechanisms available to the shear response are not available to the bulk response – a conclusion that is consistent with work by Bero and Plazek but that differs from Leaderman's hypothesis and similar arguments made by other researchers. Figure 1: Comparison of bulk and shear responses for a polystyrene; after ref. 1. Y. Meng and S. L. Simon, J. Polym. Sci: Part B: Polym. Phys., to appear, 2007. P. K. Agarwal, Ph.D. Thesis, University of Pittsburgh, Pittsburgh, PA, 1975.

  2. Sindee L. Simon, Texas Tech University, DMR 0606500 Education: Two Ph.D. graduate students, Yan Meng and Prashanth Badrinarayanan, have thus far been supported on this grant. The students are measuring the volumetric response after pressure and temperature jumps using pressurizable and conventional dilatometry, respectively. Three refereed journal articles have been published, accepted, and/or submitted to date.1-3 Yan Meng at the control computer for the custom-built pressurizable dilatometer. Outreach and Broader Impact: Outreach has included presentations by the PI and the graduate students on the findings of this project at various local, national, and international meetings, including the meetings of the Society of Plastics Engineers, American Physical Society, and the Texas Section of the North American Thermal Analysis Society. 1. P. Badrinarayanan, W. Zheng, and S. L. Simon, Thermochimica Acta, submitted, June 2007. 2. Y. Meng and S. L. Simon, J. Polym. Sci.: Part B: Polym. Phys., accepted for publication, July, 2007. 3. P. Badrinarayana, W. Zheng, Q. X. Li, and S. L. Simon, J. Non-Cryst. Solids, 353, 2603 - 2612 (2007). Yan Meng at his poster at the 2007 American Physical Society Meeting.

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