Artefacts and their healing in ultramicrotomy of side-chain liquid-crystal polymers

When sectioned by ultramicrotomy, a polymer undergoes compression forces that can modify its structure. In this paper, this was clearly established in the case of a side-chain smectic A polymer (PMA) well oriented by a magnetic field, by comparison of the X-ray diffraction pattern with the electron diffraction pattern. A study of these patterns with respect to the sectioning directions leads to the conclusion that the side chains are tilted by the knife edge of the ultramicrotome. This effect is regular and homogeneous all over the section. When annealed in the smectic temperature range, the sections recover their original smectic A structure. However, high-resolution electron microscope images show that disorder has been introduced by this process at a microscopic level.