Relaxation of anisotropic thermal diffusivity in a polymer melt following step shear strain

Forced Rayleigh light scattering is used to examine anisotropic thermal hea t conduction due to deformation in a polymeric liquid. Thermal diffusivity is measured in both the flow and neutral directions in a polyisobutylene me lt 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 val ue. Comparison of the difference between measured flow and neutral directio n thermal diffusivities with the analogous Row-induced birefringence suppor ts arguments for a proportionality between stress and thermal diffusivity.