Structural investigation of poly(3-hydroxybutyrate) spherulites by microfocus x-ray diffraction

A banded spherulite of bacterial poly(3-hydroxybutyrate) (band spacing 120 microns) (see polarized-light optical micrograph in the figure) is linearly scanned along the radial direction in 3 microns steps by means of microfocus X-ray diffraction using a synchrotron source. A large no. of X-ray diffraction patterns are collected inside each band. Those taken at the center of the bands represent the two limit diffraction patterns, from which the exact orientation of the unit cell can be evaluated. The data show that the unit cell mean position smoothly rotate around the a axis with increasing distance from the spherulite center.