Journal of Colloid and Interface Science, Vol.311, No.1, 237-242, 2007
Fourier transform infrared investigation on the state of water in reverse micelles of quaternary ammonium gemini surfactants C-12-s-C-12 center dot 2Br in n-heptane
The state of waterin the reversemicelles of C-12-S-C-12 center dot 2Br homologues has been investigated by Fourier transform infrared spectroscopy. The results showed that the solubilized water had four states: the quaternary ammonium head-group-bound, the Br- -bound, the bulklike, and the free water. With increasing W-0, the number of bulklike water per surfactant (nb) rapidly increased, which indicated swelling of the reverse micelle. The number of the head-bound water per surfactant (n(N+)) gradually increased. This was attributed to a reduction of the interfacial curvature, which permitted more water molecules to associate with the ionic heads of surfactants and also led to a part of n-hexanol being expelled from the interface and thus water filled up. Owing to the existence of n-hexanol in the interface, the head-bound water of the present system was smaller than that of AOT system at the same W-0. The number of counterion-bound water per surfactant (n(Br-)) remained unchanged with W-0. This was due to much smaller dissociation of the head Of C-12-2-C-12 center dot 2Br than that of AOT. With increasing s, unchanged n(N+) is attributed to the comprehensive effects of enlarged head, which promotes the hydration, increased ionization degree, and reduced size of the water pool. Owing to increased ionization degree, n(Br-) increases with s. (C) 2007 Elsevier Inc. All rights reserved.