Molecular Reorientation in PDLC Films Monitored by (2)H-NMR: Electric Field Induced Reorientation Mechanism and Optical Properties

The molecular orientation in Polymer Dispersed Liquid Crystals (PDLC) was monitored by (2)H-NMR of a dissolved deuterated probe molecule in the presence of an applied electric field of variable intensity. Data of molecular orientations at different applied fields were extracted from NMR lineshapes by comparison with spectra at zero field. Such data were quantitatively analyzed using an empirical function. By comparison with optical data we concluded that the molecular reorientation due to the electric field is achieved by distortion of the minimum energy director configuration. With these highly distorted configurations the light transmission through films of the material is still low and the optical switching is in general at higher fields, when the majority of molecules are oriented along the electric field. Correlations between the reorientational switching voltage and the sharpness of the reorientation have been found and tied to the role played by different factors in orienting the liquid cristal director.