[en] The sizes and structures of micelles formed in aqueous solutions of cationic octadecyl trimethyl ammonium chloride (OTAC) and anionic ammonium dodecyl sulfate (ADS) surfactants were investigated using small angle neutron scattering (SANS), self-diffusion coefficients by pulsed-gradient spin-echo (PGSE) NMR, and dynamic light scattering (DLS) methods. SANS and DLS data indicate that their structures are spherical at concentrations as high as 300 mM. As the total surfactant concentration increases, the peaks of SANS spectra shift to higher scattering vector and become sharper, indicating that the intermicellar distance decreases and its distribution becomes narrower. This is due to more compact packing of surfactant molecules at high concentrations. The intermicellar distance of around 100 A above 200 mM corresponds approximately to the diameter of one micelle. The sizes of spherical micelles are 61 A and 41 A for 9 mM OTAC and 10 mM ADS, respectively. Also the self-diffusion coefficients by PGSE-NMR yield the apparent sizes 96 A and 31 A for micelles of 1 mM OTAC and 10 mM ADS, respectively. For ADS solutions of high concentrations (100-300 mM), DLS data show that the micelle size remains constant at 25 ± 2 A. This indicates that the transition in micellar shape does not take place up to 300 mM, which is consistent with the SANS results

[en] Phase behavior for the mixed aqueous surfactant systems of cationic octadecyl trimethyl ammonium chloride (OTAC)/anionic ammonium dodecyl sulfate (ADS)/water was examined. Below the total surfactant concentrations of 1.5 m molal, mixed micelles were formed. At the total surfactant concentrations higher than 1.5 m molal, there appeared a region where mixed micelles and vesicles coexist. As the surfactant concentration increased, the systems looked very turbid and much more vesicles were observed. The vesicles were spontaneously formed in this system and their existence was observed by negative-staining transmission electron microscopy (TEM), small-angle neutron scattering (SANS) and encapsulation efficiency of dye. The vesicle region was where the molar fraction α of ADS to the total mixed surfactant was from 0.1 to 0.7 and the total surfactant concentration was above 5 x 10^-4 molality. The size and structure of the vesicles were determined from the TEM microphotographs and the SANS data. Their diameter ranged from 450 nm to 120 μm and decreased with increasing total surfactant concentration. The lamellar thickness also decreased from 15 nm to 5 nm with increasing surfactant concentration and this may be responsible for the decrease in vesicle size with the surfactant concentration. The stability of vesicles was examined by UV spectroscopy and zeta potentiometry. The vesicles dI_splayed long-term stability, as UV absorbance spectra remained unchanged over two months. The zeta potentials of the vesicles were large in magnitude (40-70 mV) and the observed longterm stability of the vesicles may be attributed to such high ζ potentials

[en] This article deals with an investigation on the phase behavior of the pseudoternary AOT/cyclohexane/0.2M AgNO₃ aqueous solution and features of Water-in-Oil (W/O) microemulsions (MEs). The sizes and structures of water pools in the microemulsions were determined by Small-Angle Neutron Scattering (SANS). SANS spectra yielded that water pools of spheres with sizes 4-10 nm and of cylinders with lengths of 25-30 nm were formed at four different compositions inside the microemulsion region. Silver nanoparticles were prepared with the microemulsions and identified by the peaks at 400 nm wavelength and types of UV/Vis absorption spectra. TEM micrographs showed that the silver nanoparticles formed were spherical and rod-like, depending on the compositions of the microemulsions and reflecting the sizes and shapes of the water pools