Abstract NMR SPDE measurements are reported for the lamellar (dispersions and multibilayer stacks) and hexagonal phases of sodium octanoate/octanol/D 2O mixtures. In the lamellar L β and L γ (gel) phases the octyl chains are rigid and perfectly ordered, while in the lamellar L α and hexagonal phases they are flexible and disordered. In particular, the measurements show that in the fluid lamellar L α phase, there is a marked discontinuity in the octyl chain flexibility at the C 5-C 6 segment; this behaviour is identical to that previously reported for the alkyl end-chains in smectic 4,4′-di- n-octyloxyazoxybenzene. In contrast, in the hexagonal phase, there is an effectively continuous flexibility gradient along the whole length of the octyl chain as in nematic 4,4′-di- n-octyloxyazoxybenzene. The behaviour in the lamellar phase is attributed to interference between cooperative conformational modes and localized random thermal fluctuations.