Order parameter profile of perfluorinated chains in a lamellar phase

Cesium perfluorooctanoate molecules are investigated by NMR spectroscopy in the lamellar phase of their aqueous solution. The particular NMR method, C -13-detected, F-19-decoupled separated-local-field (SLF) spectroscopy, prov ides the dipolar splitting of each C-13 spin to its F-19 neighbors. These d ipolar splittings are interpreted in terms of the molecular C-F bond order parameters of each difluoromethylene and trifluoromethyl group. The obtaine d variation of this order parameter along the fluoroalkyl chain strengthens the conclusion from an earlier, model-dependent study (Fur6, I.; Sitnikov, R. Langmuir 1999, 15, 2669): perfluorinated surfactant chains are signific antly more rigid than their hydrogenated counterparts.