Study on the Order Parameters of Dichroric Dyes Dissolved in Liquid Crystals

The relations among order parameters of dichroric dyes in guest-host cells, their molecular length and width, molecular dipole moment and induced dipole moment were studied. The order parameter (S) increases with length (l). When l increases to a certain value, the S increases slowly, if l of dye molecule is much longer than the l of liquid crystal molecule the S will tend to decrease. In E_7 (mean value of molecular length of the liquid crystal is 1.4nm), if dye molecular length reaches 2.3 nm, the S will approach saturation. Since the side substitution group increases its width the S will be decreased. The S of guest-host cell increases with the increase of dipole-moment between the molecules of the liquid crystal. The higher the order parameter of the G. H. cell is, the larger the dichroic ratio, generally, the higher its color contrast.