Dynamic fourier transform infrared spectroscopy of liquid‐crystalline elastomers

The influence of mechanical deformation on the orientation behaviour of the phenyl benzoate mesogenic groups in polyacrylate‐ and polymethacrylate‐based liquid‐crystalline (l. c.) elastomers with spacers of six methylene units is investigated as a function of temperature and time by means of linear‐dichroism infrared spectroscopy. The mesogens in the polymethacrylate elastomers preferably align perpendicular to the stretching direction and show a biaxial phase with homeotropic orientation. The changes in sample geometry, especially the film‐thickness variation during deformation, are studied. The orientation behaviour of the mesogens in the polyacrylate elastomers is different in the nematic and smectic phase. On stretching, the mesogens align parallel in the nematic and perpendicular to the stretching direction in the smectic phase. The orientation of a film stretched in the smectic phase, however, changes to be parallel to the stretching direction if its temperature is raised once above the smectic‐to‐nematic transition temperature. The dynamics of reorientation of the mesogens strongly depends on temperature. With high mobility of the mesogens no phase lag between deformation and orientation can be detected on a timescale of 100 ms. The orientation behaviour of l. c. elastomers is very complex and depends on many parameters, each of which is important.