摘要:

The liquid crystal phases occurring with the cationic surfactants dodecyltrimethyl ammonium chloride (C12TAC) and hexadecyltrimethyl ammonium chloride (C16TAC) in water have been examined using differential scanning calorimetry, low-angle X-ray diffraction and, in particular, multinuclear magnetic resonance spectroscopy. The dependence of water (2H2O), chloride (35Cl), and surfactant (14N) quadrupole splittings (δ) on composition in the hexagonal and lamellar phase has been determined. For C12TAC, from the14N δ values, the location and ordering of the NMe3+was found to be almost independent of composition for the H1phase, whereas at the higher surfactant concentration within the Lαphase the order increased gradually. Within the H1phase the35Cl δ values are highly sensitive to composition and temperature. This implies that the chloride ions reside between the head groups at the highest water concentrations and are squeezed out as temperature or surfactant concentration increases. Water2H δ values show a maximum as a function of composition allowing an estimate of 4·3 bound water molecules per surfactant for the H1phase and > 2 bound for the Lαphase to be made. For C16TAC X-ray diffraction data shows that the gel phase occurring below 40°C has an interdigited monolayer structure. At temperatures above the gel phase, H1and Lαphases occur, these being separated by V1or intermediate phases. Broadly, similar NMR quadrupole splittings to those found for C12TAC were measured for the H1and Lαphases of C16TAC. Only2H δ measurements could be made on the gel phase. The values are generally larger than those for the Lαphase, indicating an increase in water ordering because of the increased order of the surfactant layer.

ISSN:0267-8292    

DOI:10.1080/02678299008047336

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor