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We investigate the segmental and local dynamics as well as the transport of Li+ cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content, using dielectric relaxation spectroscopy. We observe a slowing down of segmental dynamics and an increase in glass transition temperature above a critical ion content, as well as the appearance of an additional relaxation process associated with rotation of ion pairs. Conductivity is strongly coupled to segmental relaxation. For a fixed segmental relaxation frequency, molar conductivity increases with increasing ion content. A physical model of electrode polarization is used to separate ionic conductivity into the contributions of mobile ion concentration and ion mobility, and a model for the conduction mechanism involving transient triple ions is proposed to rationalize the behavior of these quantities as a function of ion content and the measured dielectric constant. [ABSTRACT FROM AUTHOR]

Volumetric measurements were carried out onn-octyloxy-cyanobiphenyl (8OCB) over temperatures from ambient to 150°C at pressures up to 200 MPa, encompassing the liquid, nematic and smectic liquid crystalline, and crystal states. From the step changes in volume at the transitions, the phase boundaries and the associated activation enthalpies and energies were determined. The results are consistent with prior studies that were limited to a narrower range of thermodynamic conditions. The thermodynamic potential parameter, Γ, found for the isotropic–nematic transition, =3.15, is significantly smaller than the scaling exponent γ (=4.4) that superposes the longitudinal relaxation times in the nematic state. From this non-equivalence, we conclude that the order parameter must vary with pressure along the clearing line. By comparing the phase behaviour of the nematic state for isochoric and isobaric conditions, the relative contribution of volume was determined to be less that the effect of thermal energy on the thermodynamic stability. [ABSTRACT FROM AUTHOR]

Polyureas, formed by the rapid reaction between isocyanatesand diamines, are attractive for various applications due to theiroutstanding mechanical properties, which can be tuned by varying componentchemistry, molecular weight, and stoichiometry. Polyureas synthesizedfrom a modified methylene diphenyl diisocyanate (Isonate 143 L) andpolytetramethylene oxide-di-p-aminobenzoate (VersalinkP1000) are widely utilized and investigated for energy absorbing applicationssuch as impact mitigation and ballistic protection. In order to developa more complete understanding of their mechanical response, we explorethe effect of uniaxial strain on the phase separated microstructureand molecular dynamics. We utilize wide- and small-angle X-ray scatteringto investigate amorphous segment and hard domain orientation, andbroadband dielectric spectroscopy for interrogation of the dynamics.Uniaxial deformation was found to significantly perturb the phase-separatedmicrostructure and chain orientation and result in a considerableslowing down and broadening of the polyurea soft phase segmental relaxation. [ABSTRACT FROM AUTHOR]

Understanding the origin of the dramatic temperature and density dependence of the relaxation time of glass-forming liquids is a fundamental challenge in glass science. The recently established 'density-scaling' relation quantifies the relative importance of temperature and density for the relaxation time in terms of a material-dependent exponent. We show that this exponent for approximate single-parameter liquids can be calculated from thermoviscoelastic linear-response data at a single state point, for instance an ambient-pressure state point. This prediction is confirmed for the van der Waals liquid tetramethyl-tetraphenyl-trisiloxane. Consistent with this, a compilation of literature data for the Prigogine-Defay ratio shows that van der Waals liquids and polymers are approximate single-parameter systems, whereas associated and network-forming liquids are not. [ABSTRACT FROM AUTHOR]