Electric-field-induced segmental reorientation in ferroelectric liquid crystalline polymers and elastomers

Macroscopically oriented ferroelectric liquid crystalline elastomers were prepared by UV-induced cross-linking of the corresponding polymer. Time-resolved FT-IR spectroscopy is employed to analyze structure and mobility in these materials on the level of the different molecular moieties. The influence of cross-linking is analyzed in detail in its effect on the molecular motion and its time dependence in response to an external electric field. The angular excursion of the motion of the spacer in response to an external electric field is much smaller than that of the mesogen. This is in pronounced contrast to low molecular FLC. The angle between the mesogen and the spacer changes continuously during the reorientation in the Sm A phase, suggesting continuous changes in the spacer conformation. It is shown that the ferroelectric order is frozen by the cross-linking reaction. A new method is described to detect the phase transition Sm C*- Sm A in ferroelectric liquid crystalline elastomers. It is based on a direct determination of the biased rotation for the polar (carbonyl) groups being the molecular origin of the observed ferroelectricity.