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Articles you may be interested inDielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture Dielectric and shear mechanical relaxation data are reported for mixtures of glycerol and n-propanol. Measurements of the dielectric permittivity were made at _60° over a frequency range from 50 cps to 600 kc/sec and indicate a distribution of dielectric relaxation times of the Davidson-Cole form. This distribution was observed to narrow with increasing n-propanol content. Shear mechanical measurements in the temperature range + 10° to -150°C and frequency range 10 to 130 Mc/sec indicate a broad distribution of times which is essentially independent of the relative concentration of the two components of the mixture.The width of the dielectric distribution is shown to be a function of the ratio of the average dielectric to shear relaxation times, TD/T s, becoming narrow as this ratio becomes large. These results are in accord with the concepts of McDuffie and Litovitz who proposed that the origin of the distribution of dielectric relaxation times is related to a cooperative breakup of the liquid structure and that the effects of this structural breakup on the dielectric process are lessened when the dielectric reorientation process takes a much longer time than the structural breakup.In pure n-propanol it is found that TD/T s is temperature dependent in contrast to a temperature-independent ratio in glycerol. In order to explain these results, it is suggested that the local free volume in n-propanol needed for dielectric orientation is larger than that needed for the shear process. Using the free-volume theory of Macedo and Litovitz it is estimated that in pure n-propanol the critical local free volume for dielectric orientation is 40% larger than the critical local free volume for shear flow.

The rheological properties, including melt viscosity, storage modulus and loss modulus of perfluoropolyether (PFPE) lubricants with different molecular weights and chain-end functionalites, were measured using a rotational rheometer. The melt viscosities of fractionated PFPEs exhibited Newtonian behavior, and increased linearly with molecular weight. For PFPE containing functional, polar endgroups there is a sharp transition in the slope for the viscosity at a critical molecular weight. We also found that the intrinsic viscosity or Huggins coefficient can be used to examine media noise developed in the manufacturing stage.

Longitudinal and shear mechanical relaxation data are reported for a hydration of 20% of synthetic diethylamine melanin. The longitudinal attenuations per wavelength αλ at frequencies between 1 and 5 MHz show an enormously large amount of absorption above room temperature. The amount αλ/2π=0.55–0.95 at a temperature of 60 °C in the frequency of 1 MHz has never been found in usual polymeric substances where αλ/2π∼0.1. The longitudinal data are interpreted in terms of a combined relaxation and resonance process. Measurements of the shear impedance in the temperature range from −10 to +60 °C, with frequencies ranging from 5.2 to 362 MHz, indicate a distribution of relaxation times, represented by the Davidson-Cole spectrum. Temperature dependency of limiting shear modulus is found to obey the Hirai-Eyring equation.