N.m.r. relaxation times of the lamellar phases of the system sodium caprylate/decanol/water

Abstract

Proton n.m.r. relaxation times have been measured for the lamellar phases (B, C and D) of the system sodium caprylate/decanol/water. A single spin lattice (T₁) curve was observed for the alkyl chain and water protons over a wide range of compositions, but separate T₁ values were obtained using samples containing D₂O. In the D phase for samples with high water content, T₁ values show that little restriction on bulk water mobility exists, and that fast exchange occurs between free and bound water. At low water content counter-ion binding gives an additional restriction on the mobility of bound water. T₁-Values for water in B and C phases are similar to those for D phase samples with high water content. Water spin-spin (T₂) relaxation times are dominated by the contribution from decanol OH protons due to decanol-water OH proton exchange. Alkyl chain proton T₁ and T₂ values are similar in the three different phases and reflect the restricted chain motions. Because of this similarity, the proposed tetragonal structure for the C phase has been critically reviewed and the evidence found to be inconclusive.

High resolution n.m.r. linewidths of water protons contain contributions from both dipolar relaxation and magnetic susceptibility broadening.