Af. Terzis et Dj. Photinos, ELECTROSTATIC INTERACTIONS IN LIQUID-CRYSTALS - ORDERING OF RIGID SOLUTES IN NEMATIC SOLVENTS, Molecular physics, 83(4), 1994, pp. 847-865
The orientational distribution of a probe molecule in a nematic solven
t is derived in terms of the intermolecular potential describing steri
c, dispersional, and electrostatic interactions with the solvent molec
ules. Orientational correlations among the latter molecules are neglec
ted in the derivation, whereas probe-solvent correlations are treated
explicitly. The theory is used to analyse NMR measurements of order pa
rameters of small solute molecules in nematic solvents. Tenser compone
nts of the solute potential of mean torque up to fourth rank are evalu
ated. The various electrostatic contributions (dipole-dipole, dipole-q
uadrupole, quadrupole-quadrupole, etc.) are assessed quantitatively. I
t is found that the residual overall electrostatic interaction is sens
itive to the configuration of the permanent electrostatic moments with
in the molecular frame and to the shapes of both the solute and the so
lvent molecules. Contributions from the induced moments are rather sma
ll. An accurate and consistent description of the measured order param
eters is obtained. The results of the calculations are used to elucida
te the limitations and discrepancies of models which describe electros
tatic interactions by attributing average properties (e.g., electric f
ield gradient) to the nematic solvent.