Precision rheometry: Surface tension effects on low-torque measurements in rotational rheometers J. Rheol. 57, 1515Rheol. 57, (2013 Rheological and morphological study of cocontinuous polymer blends during coarsening J. Rheol. 56, 1315Rheol. 56, (2012 Sphere motion in ordered three-dimensional foams J. Rheol. 56, 473 (2012) The work of adhesion of polymer/wall interfaces and its association with the onset of wall slip J. Rheol. 42, 795 (1998) Extensional rheometry of polymer multilayers: A sensitive probe of interfaces Synopsis When shear oscillations are performed with melts of polystyrene (PS)I poly(methylmethacrylate) (PMMA) blends the total deformation has a large elastic portion at low frequencies. This finding is caused by the interfacial tension acting between the two phases of the blends. A simple model allows one to describe the influence of the interfacial tension on the storage and the loss moduli in a broad frequency range for all mixing ratios of the blend components. The weighted relaxation spectra rH( r) of such blends show an additional peak with a characteristic relaxation time that is correlated with the interfacial tension. From this characteristic relaxation time the interfacial tension a between the melts of PS and PMMA can be determined, The resulting a = ( 1.9 ±O.3) X 10-3 N/m at 170'C is in good agreement with the value obtained from recovery following melt elongation of the blends.
Microvatistors are small sintered particles of doped 2110 with strongly nonlinear electrical properties similar to those of the varistor ceramics. Composite materials based on a silicone matrix filled with microvaristor powder have a nonlinear current-voltage relation and can be used for field grading applications. The field dependence of the conductivity is determined by the properties of the filler panicles, and can be tuned by modifying the formulation of the microvaristors and the sintering conditions as sintering time or temperature. In this Contribution, we describe the nonlinear field grading material, and report on the development of a prototype field-grading element for a dry and compact high voltage termination, which has been successfully tested.
Microvaristors are tiny electroceramic particles, which have highly nonlinear, voltage controlled electrical transport properties and can be used as active fillers in a variety of insulating matrix materials for functional composites. Due to the internal grain boundary structure, each individual microvaristor particle shows an IV-characteristics similar to the one known from bulk ceramics, except for the scaled down switching voltage. By controlling the material formulation, the particle morphology and the sintering conditions the switching characteristics of microvaristors can be tailored for specific applications.In the present paper the basic properties of ZnO microvaristors are described and it is shown how they impart their nonlinearity to the composite. A single microvaristor can withstand surprisingly high current loadings, without major changes in their electrical properties. Combined with the high manufacturing flexibility known from polymer processing, the varistor composites can be used for new solutions in overvoltage protection or control of electrical fields.
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