Anisotropic thermal transport in a crosslinked polyisoprene rubber subjected to uniaxial elongation

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2012-12, Vol.50 (23), p.1638-1644
• Main Authors: Simavilla, David Nieto, Schieber, Jay D., Venerus, David C.
• Format: Article
• Language: English
• Subjects: anisotropic; Anisotropy; Applied sciences; crosslinked polymer; Crosslinking; elastomer; Elongation; Exact sciences and technology; Natural polymers; Natural rubber; Physicochemistry of polymers; Polyisoprenes; rubber; Thermal conductivity; Thermal diffusivity; thermal properties; Transport
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.23173

Anisotropic thermal transport in a crosslinked polyisoprene (natural rubber) subjected to uniaxial elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two components of the thermal diffusivity tensor are measured as a function of stretch ratio. The thermal diffusivity is found to increase in the direction parallel, and decrease in the direction perpendicular, to the stretch direction. The level of anisotropy for the natural rubber is substantially lower than that reported by Tautz 50 years ago but comparable to that found in our previous studies on molten polymers, quenched thermoplastics, and other crosslinked elastomers. Thermal diffusivity data along with measurements of the tensile stress were used to evaluate the stress‐thermal rule, which was found to be valid over the entire range of stretch ratios. In contrast, failure of the stress‐optic rule was observed at stretch ratios well below the largest value at which the stress‐thermal rule was valid. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and stretch of polymer chain segments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 To examine the validity of the stress‐thermal rule for large deformations of natural rubber, as well as the apparent universality of the stress‐thermal coefficient, anisotropic thermal conduction in a crosslinked polyisoprene subjected to uniaxial elongation is studied. Using an optical technique based on Forced Rayleigh Scattering, components of the thermal diffusivity tensor parallel and perpendicular to the direction of elongation have been measured as a function of elongation ratio. It is observed that the stress‐thermal rule is valid for deformation levels at which the stress‐optic rule fails.