¹⁹F Multipulse NMR Study of Some Amphiphilic Liquid Crystals

Abstract Multipulse NMR techniques have been used to investigate the dynamic properties of cesium perfluoro-octanoate (CsPFO) and ammonium perfluoro-octanoate (APFO) + water systems, which are liquid crystals over a wide range of temperature and concentration. Axially symmetric fluorine chemical shift tensors have been measured for the CF2 and CF3 groups, with respect to a C6F6 internal reference, by performing a rotation study of an aligned sample (50% CsPFO: 50% D2O) at room temperature. By fitting experimental spectra the order parameter Sr relative to 50% CsPFO: 50% D2O at room temperature, has been determined for 70% APFO: 30% D2O and 72.2% CsPFO: 27.8% D2O in the lamellar mesophase over a temperature range 20°C-85°C. A model is assumed in which wagging motion of the molecular chain leads to scaling of the shift anisotropy. The order parameter S has been estimated using known values of the 19F chemical shift tensor elements for CF2 groups in teflon at liquid nitrogen temperature.

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