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Abstract
A study of the dynamics of the lipid molecules in the nematic lyotropic liquid crystal system composed of 30 per cent (by weight) potassium laurate-αd 2, 6 per cent decanol, 4 per cent potassium chloride and 60 per cent water was carried out using deuteron N.M.R. The quadrupolar splitting v Q of the N.M.R. spectrum, the decay T 2e of the quadrupolar echo the decay T 1Q of the quadrupolar energy and the return T 1Z of the Zeeman energy were measured as functions of temperature throughout the nematic region. The v Q values show that the order parameter for the α position of the laurate chain decreases from 0·17 to 0·11 with increasing temperature. There are two contributions to the observed values of T 2e. The time averaged dipolar interaction between the α deuterons and neighbouring protons results in a roughly constant contribution while the time dependent quadrupolar interaction causes a marked decrease in T 2e near the low temperature phase boundary. An analysis of the quadrupolar contribution suggests that there is a molecular motion with a correlation time which ranges from 10-7 to 10-9 s in the nematic phase. The spin-lattice relaxation times T 1Z and T 1Q can be analysed to obtain the spectral density functions J 1(ω0) and J 2(2ω0) separately. There again appears to be two competing relaxation mechanisms responsible for the observed results. One of these involves fluctuations of the lipid molecules as rigid rods about the normal to the bilayers.
The addition of small amounts of benzene to the mixture (up to 2 per cent) caused a marked decrease in the temperature range of the nematic phase.
