An advanced broadband dielectric relaxation spectroscopy technique was developed to measure dipolar reorientation dynamics in an actively deforming amorphous polymer below the glass transition temperature. The application of a weak oscillating electric field during deformation allows for direct probing chain segment mobility. Results show that the application of a monotonically increasing strain on a glassy poly(vinyl chloride) induces a significant increase of the out-of-phase dielectric permittivity, thereby reflecting enhancement of the transition activity of chain segments. Moreover, the strain-dependent relaxation spectra suggest that the bifurcation of the relaxation processes decreases together with an overall increase in molecular mobility upon active deformation. The dielectric results also display a highly pronounced sensitivity to the apparent strain rate used for the mechanical excitation and isothermal aging prior to the deformation.

The mechanisms by which hydroxyapatite nanofiller promotes reinforcement in poly(vinylacetate) matrix is investigated. Hydroxyapatite nanofillers with spherical and platelet particle shape were synthesized. Particle size was in the range from 5 to 60 nm. Filler concentration in composites was limited to maximum of 5 vol% to minimize filler networking. Effect of the nanofiller particle shape on the elastic response of nanocomposite was examined using dynamic-mechanical thermal spectroscopy. Attempt to interpret the observed phenomena was based on the molecular approach. POLYM. COMPOS., 28: 365-371, 2007.

Dynamic-strain softening known as the Payne effect was investigated in the case of poly(vinyl acetate)-hydroxyapatite (PVAc-HA) model nanocomposites in which the nanoparticles served as reversible physical crosslinks. HA nanofillers with different particle shape and with size ranging from 5 to 60 nm were used. Filler concentration in PVAc nanocomposites was limited to maximum of 5 vol%. Dynamic-mechanical spectra were recorded as a function of structural variables, strain amplitude, and test temperature using the dynamic-mechanical thermal spectroscopy (DMTS). Additionally, amplitude sweep tests were supplemented by the modulus recovery experiments to provide relaxation time data. Observed phenomena were interpreted using polymer physics approach. POLYM. COMPOS., 28:743-747, 2007. POLYMER COMPOSITES--2007 FIG. 9. Terminal recovery time of nanocomposite G 0 -filler surface area in one gram of nanocomposite sample dependence for PVAc nanocomposite with spherical and platelet HA nanofiller at 908C.

No abstract

No abstract