Undulations and fluctuations in a lamellar phase lyotropic liquid crystal and their suppression by weak shear flow.

Using multi-echo pulsed gradient nuclear magnetic resonance (NMR) we measure the anisotropic diffusion of water molecules in the lamellar phase of lyotropic system composed of cetylpyridinium chloride/hexanol diluted in brine. The technique reveals the Fourier spectrum of the molecular velocity autocorrelation function, and its repetitive compensating nature permits effective measurement in the presence of shear flow. We show that under zero shear the phase is highly oriented and that both the amplitude and fluctuation correlation time of lamellar undulations can be measured. The suppression of undulations by weak shear is apparent. We further measure transverse lamellae permeability arising from defects.