Small-angle x-ray scattering from amorphous polycarbonate

Small-angle x-ray scattering (SAXS) from amorphous polycarbonate (PC) exhibits a sharp rise in intensity at ultrasmall angles (2θ <0.08° for Cu Kα radiation). At much higher angles, SAXS is superimposed on a diffuse halo centered at an angle corresponding to a spacing of [inverted lazy s]10 Å. Since doping the PC with small amounts of I2 results in a reversible decrease in SAXS intensity, SAXS is not due to voids but is probably attributable to the ``nodule'' structure observed in PC with electron microscopic techniques. The invariant, ∫0∞θ2I(θ)dθ and lim[θ4 I(θ)] as θ → ∞, are used to compute a specific surface of 150 m2/cm3 based on the assumption of 0.5 volume fraction of spherical nodules. The ``range of inhomogeneity'' of the nodules is then found to be 130 Å. From absolute intensity measurements the minimum relative density fluctuation between the nodules and their surroundings is 1.6%; an upper limit of 1.8% is found for fcc close packing of nodules. This result demonstrates that the model of Yeh, which assumes crystalline density for the nodules and predicts a relative density fluctuation of 21% is much too extreme.