Investigation of the structural deformation mechanisms induced by microindentation in a thermotropic liquid crystalline copolyester using synchrotron x-ray microdiffraction

The structural changes induced by microindentation on thermotropic liquid crystalline copolyester fibers of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) have been investigated by scanning X-ray microdiffraction techniques at the ESRF microfocus beamline (ID13). A phase transformation is observed upon deformation from a pseudohexagonal lattice (P-H) to two distinct orthorhombic phases (O-I, O-II). In addition, a strong texture is observed in the plastically deformed region as revealed by changes in the local orientation of the crystalline domains in the vicinity of the indenter tip and the appearance of reflections in specific directions only. This allows quantifying the extent of the deformation both across and along the fiber and also suggests the presence of complex structural processes occurring during indentation tests.