J. Phys. II France
Volume 6, Numéro 6, June 1996
Page(s) 845 - 871
DOI: 10.1051/jp2:1996215
J. Phys. II France 6 (1996) 845-871

On the Influence of Director Fluctuations on NMR Relaxation in Liquid Crystals

E.A. Joghems and G. van der Zwan

Department of Chemistry, Vrije Universiteit van Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands

(Received 16 October 1995, received in final form 12 February 1996, accepted 27 February 1996)

We investigated and extended models describing the influence of director fluctuations (DF) on the orientational dynamics of individual (dissolved) molecules. The models are divides in two categories. On one hand the traditional models, relying on a seperation in time scales between the DF and the individual motion of the molecule. On the other high ordering models, which assume the motion of the individual molecule is very similar to the DF. The spectral densities calculated from all models were fitted to NMR relaxation data. It is found that virtually all result in acceptable fits for the frequency of J1. Comparison to (sparsely available) J2 data proves to be a much more severe test of the different models. From this we see high ordering models are inadequate. The traditional model gives a slightly better fit, although the calculated frequency dependence in J2 is generally too small, which is actually caused by an overestimation of the effect of DF on J1. Only the extended traditional model result in reasonable agreement between experimental and calculated curves.

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