We have examined the linear rheological responses of a series of well-defined, dense, regularly branched brush polymers. These narrow molecular weight distribution brush polymers had polynorobornene backbones with degrees of polymerization (DP) of 200, 400, and 800 and polylactide side chains with molecular weight of 1.4 kDa, 4.4 kDa, and 8.7 kDa. The master curves for these brush polymers were obtained by time temperature superposition (TTS) of the dynamic moduli over the range from the glassy region to the terminal flow region. Similar to other long chain branched polymers, these densely branched brush polymers show a sequence of relaxation. Subsequent to the glassy relaxation, two different relaxation processes can be observed for samples with the high molecular weight (4.4 and 8.7 kDa) side chains, corresponding to the relaxation of the side chains and the brush polymer backbone. Influenced by the large volume fraction of high molecular weight side chains, these brush polymers are unentangled. The lowest plateau observed in the dynamic response is not the rubbery entanglement plateau but is instead associated with the steady state recoverable compliance. Side chain properties affect the rheological responses of these densely branched brush polymers and determine their glassy behaviors.

Abstract-Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems. HVDC cables, in particular, play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability. In this paper, the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed. The non-uniform electric field distribution caused by the applied voltage, temperature dependent conductivity, and space charge accumulation is briefly discussed. Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cables.

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SynopsisUsing self-designed particle visualization instrumentation, startup shear and step strain tests were conducted under a series of systematically varied rheological and geometrical conditions, and the velocity profiles of three different well-entangled polybutadiene/oligomer solutions were obtained. For startup shear tests, in the regime of entanglement densities up to 89 and Weissenberg numbers up to 18.6, we generally observe either wall slip and a linear velocity/strain profile or simply the linear profile with no wall slip unless a massive edge fracture or instability has occurred in the sample. Meanwhile, step strain tests were conducted under similar and higher step Weissenberg numbers, and little motion was observed upon cessation. These results lead us to a conclusion that there is no compelling evidence of shear banding or non-quiescent relaxation in the range of entanglement density and Wi investigated; we interpret the results to imply that any observed banding probably correlates with edge effects, and these probably are also present in the work of the S. Q. Wang group, and they lead to shear banding.

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The linear rheological responses of a series of specially designed wedge-type polymers synthesized by the polymerization of large molecular weight monomers have been measured. These wedge polymers contained large side groups which contained three flexible branch chains per polymer chain unit. The master curves for these polymers were obtained by time temperature superposition of dynamic data at different temperatures from the terminal flow regime to well below the glass transition temperature, T g . While these polymers maintained a behavior similar to that of linear polymers, the influence of the large side group structure lead to low entanglement densities and extremely low rubbery plateau modulus values, being near to 13 kPa. The viscosity molecular weight dependence was also somewhat higher than that normally observed for linear polymers, tending toward a power law near to 4.2 rather than the typical 3.4 found in entangled linear chains. The glassy modulus of these branched polymers is also found to be extremely low, being less than 100 MPa at T g 260 C. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B:Polym. Phys. 2015, 00, 000-000KEYWORDS: branched; glassy polymers; macromonomers; rheology; viscoelastic properties; viscosity INTRODUCTION Polymer architecture has long been known to greatly affect the rheological properties of polymeric materials and, for simple linear chains, the reptation model has been highly successful in predicting the rheological behaviors.

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Debye process and dielectric state of an alcohol in a nonpolar solvent J. Chem. Phys. 134, 044525 (2011); 10.1063/1.3543713 Finite-element modeling method for the study of dielectric relaxation at high frequencies of heterostructures made of multilayered particle J. Appl. Phys. 102, 124107 (2007) Dielectric spectroscopy is a powerful tool to study dipole relaxation, electrical conduction, and structure of molecules. Electrode polarization, as a parasitic effect due to the blocking of charge carriers in the vicinity of an electrode, can make the frequency response at low frequency difficult to understand. Since charge carriers in mineral oil are not only generated from dissociation but also from injection at electrodes, current induced by motion of injected charge carriers should also be taken into consideration. The polarization caused by the injection current has been studied in this paper. When the electric field is not intense, the injection current is proportional to the field and only contributes to the imaginary part of the complex permittivity. A new model has been proposed with this injection current being involved. The frequency responses of three different kinds of mineral oils have been measured and this new polarization model has been used to fit the experimental data. According to the simulation result, the frequency-dependent curves of complex dielectric permittivity calculated from the polarization model could fit the experimental data well. The amount of the injected charge carriers increases with the aging time. This new model enables one to gain a better understanding of electrical conduction in mineral oil. V C 2014 AIP Publishing LLC.