Forced Rayleigh light scattering is used to examine anisotropic thermal heat conduction due to deformation in a polymeric liquid. Thermal diffusivity is measured in both the flow and neutral directions in a polyisobutylene melt following the imposition of a step shear strain. The thermal diffusivity in the flow and neutral directions increases and decreases, respectively, immediately following the deformation before relaxing to an equilibrium value. Comparison of the difference between measured flow and neutral direction thermal diffusivities with the analogous flow-induced birefringence supports arguments for a proportionality between stress and thermal diffusivity.

• Received 5 October 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.366