Aklyl Chain Order Parameters and Phase Diagrams for Systems Containing Sodium n-Octanoate,Water, and Different Alcohols

Lamellar liquid crystalline phases containing sodium n-octanoate, water, and an alcohol have been studied by means of ²H NMR. Order parameters have been determined for the octanoate alkyl chain in systems containing ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol or 1, 8-octandiol. The straight chain alcohols yield decreasing octanoate order parameters with decreasing chain length. With 1, 8-octandiol the octanoate order parameters are somewhat smaller than with 1-propanol, indicating quite flexible octanoate hydrocarbon chains. Using mono-deuteriated benzyl alcohol. C₆H₅CHDOH, the S_CD as well as the S_HD (= S_HH ) order parameters were determined in the same measurement. A typical measurement yields |S _HD|-|S_CD | = 0.04 ± 0.04, where the error estimation includes the uncertainties in the quadrupole and the magnetic dipole-dipole coupling constants. It is stressed that in order to ascertain a significant difference between S_HH and S_CD , it is necessary to know the coupling constants with high accuracy. The phase diagram for the system sodium n-octanoate/water/benzyl alcohol was determined, mainly by ²H and ²³Na NMR.