A MODIFIED OPTICAL SCHLIEREN TECHNIQUE FOR MEASURING THE MUTUAL DIFFUSION-COEFFICIENT IN POLYMER BLENDS

We have developed a modified optical schlieren technique (MOST) for measuring the mutual diffusion coefficient D in miscible polymer blends. A laser light source impinges on the interface of a diffusion couple, and the intensity of refracted rays is detected with an optical multichannel analyzer interfaced with a vidicon detector. The mutual diffusion coefficient is determined by simply measuring the angular deviation of the refracted rays as a function of annealing time. As an experimental test, we measure D at 112 °C for a polystyrene (PS):poly(vinyl methyl ether) blend at 0.35 volume fraction PS. The square of the angle of the maximum deflected rays θmax is shown to vary inversely with annealing time. From a plot of θmax2 versus t−1, the mutual diffusion coefficient is measured, D = 1.1 × 10−9 cm2/s. © 1990, American Chemical Society. All rights reserved.