Abstract
This research addresses experimental issues arising in SANS diffusion studies of bulk polymers. Sample preparation, annealing protocols, reproducibility of replicate samples, data reduction, and analysis procedures are considered. Experimental SANS data for 68000 MW polystyrene are examined in detail. These data were obtained on specimens containing 50 wt % protonated and deuteriated polymer. The initial specimens were heterogeneous, containing domains of protonated and deuteriated polystyrene. Heterogeneities were destroyed, by interdiffusion, during sample annealing at 130°C. SANS results, made as a function of annealing time, were analyzed to characterize diffusion. This analysis yielded diffusion coefficients that appeared to increase with scattering angle: values between 9 × 10 -16 and 1.8 × 10 -15 cm 2 /s were obtained over the range Q = (4.0-8.0) × 10 5 cm -1 . We attribute this apparent Q dependence to instrumental effects, specifically, to "smearing" of experimental data. Simulation of scattering results, using an appropriate "smearing" function, generates values that match experiment. Simulation indicates that "smearing" has a minimal effect on diffusion coefficients measured at higher scattering angles. A constant (Q-independent) value D = 1.8 × 10 -15 cm 2 /s is suggested for 68 000 MW polystyrene at 130°C. © 1987 American Chemical Society.