The temperature dependence of chain disorder in potassium palmitate-water. A deuterium NMR study

Abstract

Quadrupolar echo deuterium magnetic resonance spectroscopy is used to study the hydrocarbon chain disorder in a 70% potassium palmitate-30% water mixture. The C-D bond order parameters are measured as a function of temperature and position along the chain. In the liquid crystalline, L α, phase the C-D bond order parameters of the methylene segments near the polar head group are found to increase with increasing temperature to a maximum at about 100°C and then decrease on further increasing the temperature. The order parameters for the remaining methylenes and the methyl group decrease monotonically with increasing temperature. The C–D bond order parameter for the α position undergoes a discontinuous change at ∼55° C and, in fact, for a 10°C range two resolvable splittings are observed for the α posittion. The low temperature, coagel, phase gives a well resolved spectrum where all methylenes are equivalent yielding a value of 168 kHz for e 2qQ/h, the quadrupole coupling constant.