Fluorocarbon surfactant/water mesomorphic phases. Part 3.—1H and 2H pulsed n.m.r. study of water in the lamellar phase of ammonium perfluoro-octanoate

Abstract

Proton and deuteron relaxation times have been measured for water in the lamellar phase of the ammonium perufloro-octanoate + water system. Changes in T₁ and T₂ with variation of temperature and composition have been determined. Water proton T₂ values indicate the presence of a proton exchange reaction between water and ammonium ions with k≃ 10²–10³ s^–1. Most of the water molecules and ammonium ions have motions similar to those of normal liquids. A fraction of water molecules is bound to the fluorocarbon surfactant head groups via hydrogen bonds. The rotational correlation time of these bound molecules is of the order of 10^–9 s and an upper limit of 10^–6–10^–7 s can be placed on the life-time of the surface-water hydrogen bonds.