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Title: Ultrasonic relaxation in some viscoelastic liquids
Authors: Narasimhan, A V
Issue Date: Feb-2003
Publisher: NISCAIR-CSIR, India
Abstract: Expressions are worked out for the ultrasonic relaxation times in viscoelastic liquids, using their compressibiity (an elastic property) and bulk viscosity coefficient (a viscous property), giving equations for the compressional and bulk viscous relaxation times in these viscoelastic liquids. Available experimental data in three viscoelastic liquids, are used to calculate these ultrasonic relaxation times , which depend upon the low, mid and high frequency wave velocities and the absorption of the wave in the medium. The complex wave velocity (Indian J Pure & Appl Phys, 12 (1974) 557) is connected with the complex compressibility or the liquid , while Navier-Stokes equations of hydrodynamics (IEEE Trans on Sonics & Ultrasonics, SU 16 ( 1969), 182) are connected with the real and imaginary parts of the complex, bulk viscosity coefficient or liquid, leading to equations for the aforesaid relaxation times and their evaluation, using experimental data. The variations of velocity, absorption and relaxation times with temperature have been discussed. Temperature variations of relaxation times have been discussed and are used to evaluate the molecular activation energies in the liquid. The magnitudes of the activation energies are found to be reasonable. The agreement between theory and experimental data seems to be better for compressional relaxation; than for relaxation associated with bulk viscosity of the liquid. It seems that, the data can be resolved into more than one relaxation group and activation energy (two or even more) leading to a distribution or relaxation times in these viscoelastic liquids.
Page(s): 105-112
ISSN: 0975-1041 (Online); 0019-5596 (Print)
Appears in Collections:IJPAP Vol.41(02) [February 2003]

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