Coherence-length anisotropy above the isotropic-to-nematic transition in a series of benzylidene anilines

The relative depolarized scattering strength and the coherence length anisotropy have been measured in a series of p-N-alkoxybenzylidene p-n-butylanilines with alkyl chain length n = 1,2,4,7, and 8. All compounds appear to obey mean-field theory. The depolarized scattering strength at a given reduced temperature (T-T*)/T* decreases with increasing chain length, whereas the free-energy parameter L2 that characterizes the anisotropy is roughly constant. There is no apparent modification in the observed pretransitional effects when the transition changes from isotropic-to-nematic (n < 8) to isotropic-to-smectic (n = 8). Copyright © 1977 American Institute of Physics.