Dj. Photinos et Et. Samulski, ELECTRIC-DIPOLE INTERACTIONS OF CHAIN MOLECULES IN NEMATICS - THE ANALYSIS OF SEGMENTAL ORDERING IN ALPHA, OMEGA-DIBROMOALKANES, The Journal of chemical physics, 98(12), 1993, pp. 9-16
The residual electric dipole interactions recently detected in the deu
terium NMR spectra of alpha,omega-dibromoalkanes dissolved in nematic
liquid crystalline solvents [J. Phys. Chem. 96, 8176 (1992)] are analy
zed in the context of the modular formulation of flexible molecule ord
ering. The chord model realization of this formulation, previously app
lied to the study of n-alkanes, is minimally extended to include the a
dditional coupling of the dipole carrying segments of the solute molec
ules to the dipolar bias produced by the solvent. The ensuing simple m
odel successfully reproduces the observed segmental order parameter pr
ofiles of the solute over the entire nematic temperature range of the
solvents. Three types of solvents are considered (Phase V, 5CB, 5OCB)
differing in their molecular dipole moment constitutions. It is found
that in all solvent cases the orientational ordering is suppressed at
the dipole moment carrying ends of the solute molecules whereas the or
dering in the main body could either be reduced or elevated depending
on the configuration of the dipole moments on the solvent molecules. Q
uantitative results for the effects of the dipolar bias on the potenti
al of mean torque are presented and the mechanism of electric dipole d
riven ordering in these solvent-solute systems is discussed.