Deuteron nuclear magnetic resonance and orientational order in binary mixtures of liquid crystals

We have observed deuteron quadrupolar splittings as a function of temperature in a series of binary mixtures of the liquid crystals 4-n-pentyl-4′-cyanobiphenyl (5CB) and 4-n-pentyl-phenylthio-4′-octyloxybenzoate (S5). The 5CB molecule is deuterated at the β-position of the alkyl chain and the S5 in the phenylthiol ring positions. The results have been interpreted in terms of a mean field theory of orientational order in binary mixtures of liquid crystals. Experimental results are in good qualitative agreement with predictions of the theory. The problems of relating order parameters for specific sites in flexible molecules as determined by deuteron nuclear magnetic resonance to the order parameters which enter mean field theories for cylindrically symmetric molecules are discussed.