Nonlinearity parameter and its relationship with thermo-acoustic parameters of polymers

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Abstract
A relationship between the isobaric, isothermal and isochoric lattice Gruneisen parameters has been examined and analysed for several polymers. Relationships between the various parameters describing the thermo-acoustic and nonlinear properties of polymers are developed and their relations with thermo-acoustic data established. It is shown that the isochoric temperature derivative of the sound speed or bulk modulus is the dominant factor, with a significant contribution to the thermo-acoustic properties. Using this simple model, Beyer's parameter of nonlinearity, thermo-acoustic parameters, molecular constant, Huggins parameter and the lattice Gruneisen parameters are shown to be related to each other. Calculated data on these parameters for eight polymers are presented. The results have been used to develop further understanding of the significance of microscopic factors such as molecular order and intermolecular interactions, upon macroscopic thermo-acoustic properties in polymers. A new dimensionless thermo-acoustic parameter S0* expressed in terms of volume expansivity only has been introduced, which gives, on an average, a constant value of 1.06 in polymers.
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