Anisotropic thermal conductivity in cross-linked polybutadienes subjected to uniaxial elongation

Anisotropic thermal transport in cross-linked polybutadienes deformed in simple 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, with a maximum anisotropy of ∼25% relative to the equilibrium value. Measurements of the tensile stress as a function of stretch ratio were also made. These data were used to show that the thermal conductivity and stress tensors are linearly related or that the stress thermal rule is valid. The value of the stress thermal coef?cient for the cross-linked polybutadiene systems was found to be consistent with previously reported values for both a cross-linked silicone rubber and polyisobutylene melts.