Calorimetric study of entropy and energy effects in small deformations of elastomers

Abstract

Deformation calorimetry was used to determine the energy and heat of uniaxial reversible elongation over the range of small deformation ( λ<1·8) for three natural rubber elastomers, a statistical copolymer of ethylene with propylene containing 45% propylene and polydimethylsiloxane rubber and in the approximation of a Gaussian chain network using the relations obtained a thermodynamic analysis was made of entropy and energy effects accompanying deformation. Overall changes of entropy and internal energy were classified as intra- or intermolecular components and it was shown that the proportion of intramolecular change in entropy and internal energy is independent of deformation and is determined by the molecular structure of the polymer. Intermolecular changes in entropy and internal energy show a marked dependence on deformation and these changes are due to volumetric variation in deformation and offset each other. Volumetric changes in deformation were calculated and thermoelastic inversion of heat and internal energy, analysed.