Generally, a microemulsion consists of oil, water, surfactant, and sometimes cosurfactant. Herein, we report a surfactant-free microemulsion (denoted as SFME), consisting of oleic acid (oil phase), water, and n-propanol without the amphiphilic molecular structure of a traditional surfactant. The phase behavior of the ternary system was investigated, showing that there were a single-phase microemulsion region and a multiphase region in the ternary phase diagram. The electrical conductivity measurement was employed to investigate the microregions of the single-phase microemulsion region, and three different microregions, that is, water-in-oleic acid (W/O), a bicontinuous (B.C.) region, and oleic acid-in-water (O/W), were identified, which were further confirmed by freeze-fracture and cryogenic transmission electron microscopy (FF-TEM and Cryo-TEM) observations. The polarity and the salt solubility of water domains in the W/O SFME were investigated by UV-visible spectroscopy using methyl orange and potassium ferricyanide as probes, respectively. Experimental results showed that the water domains in the W/O microemulsion had a lower polarity than bulk water and a normal solubility for salt species, indicating that the SFMEs have much significance in the preparation of various nanomaterials.
A new and simple method is used to control formation of gold nanoparticles in lyotropic liquid crystal. Triangular or hexagonal nano- and micro-plates can be obtained in PEO–PPO–PEO-based hexagonal liquid crystals after adding a small amount of cationic surfactant, CTAB. All plates are single crystals and mostly characterized by orientation along the [-111] direction. Their sizes are even longer than 10 μm. The selective adsorption of CTAB on certain crystallographic facets is the main point of supposed mechanism.
Positively charged silver nanoparticles capped by cetyltrimethyl ammonium bromide (CTAB) are prepared in aqueous solution. The structure of capping agents on Ag particles is systematically characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). It suggests that CTAB molecules form a bilayer shell on Ag surface with a 1:5 rough ratio of inner/outer molecules.
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