Undulation properties of the lamellar phase of a diblock copolymer:: SAXS experiments

We report on X-ray scattering results on an oriented lamellar single crystal of a diblock copolymer melt of poly(dimethylsiloxane)-b-poly(ethylene propylene). From the Bragg peak position, q(0), we calculate the temperature dependence of the lamellar period and show that it is in agreement with the values obtained using literature values of the Flory-Huggins parameter, chi. We observe the predicted diffuse scattering affecting the profile of the Bragg peak, which is related to the layer splay and compressional elasticity. We show that extremely small misalignments of the lamellar planes prevent a quantitative calculation of the layer compressibility modulus, B, and we explain this effect qualitatively using the mosaicity theory.