Time-resolved infrared spectroscopy of nematic-liquid-crystal electro-optic switching - art. no. 031707

Time resolved infrared (IR) vibrational absorption spectroscopy is used to probe the dynamics of electric held-induced reorientation of the biphenyl m olecular core and alkyl tail subfragments of the nematic liquid crystal 5CB (4-pentyl-3-cyanobiphenyl). The planar to homeotropic transition, induced by application of an electric field step to high pre-tilt planar aligned ce lls, is studied for switching times ranging from 200 mus down to 8 mus, the latter a factor of 1000 times faster than any previous nematic IR study. T he reorientation rates of the core and tail are found to be the same to wit hin experimental uncertainty, and scale inversely with applied field square d, as expected for the balance of field and viscous torques. Thus any molec ular conformation change during switching must relax on a shorter time scal e. A simple model shows that these data eliminate the possibility of there being substantial differences between the reorientational dynamics of the t ails and cores on the time scales longer than on the order of 10 mus.