Translational diffusion of rubrene and tetracene in polyisobutylene

The translational diffusion coefficients of rubrene and tetracene in amorphous polyisobutylene (PIB) were measured using the holographic fluorescence recovery after photobleaching technique. Over the temperature range from 400 to 235 K (T _g =205 K), tracer diffusion coefficients from 10^–7 to 10^–14 cm²/s were observed. These diffusion coefficients have essentially the same temperature dependence as the rotational correlation times for these two probes in PIB. Both of these observables have a slightly stronger temperature dependence than does the viscosity. These results contrast strongly with the results of similar experiments on polystyrene and polysulfone. These results are consistent with the hypothesis that local segmental dynamics are more spatially homogeneous in PIB than in polystyrene and polysulfone.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.