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A micellar surface charge modification for the regular solution theory was performed by considering the counterion bind effect. For mixed micelles of cationic fluorocarbon-nonionic hydrocarbon surfactants, this modified equation can be tested by measuring the mixed cmc, surface potential, aggregation number, and molar volumes. The mixed cmc curves are well fitted with the calculated curves by the modified equation as a function of cationic surfactant molar fraction. The interaction between the surfactants is not so repulsive as expected from the regular solution theory. In addition, the mixed micelles with various mole fractions exist in a wide mixing region and the size of mixed micelles having charge is fairly small.

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Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb(3)Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a (7)Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm∕3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.