Lyotropic Liquid-Crystalline Phase of Oligo(ethylene oxide) Surfactant/Transition Metal Salt and the Synthesis of Mesostructured Cadmium Sulfide
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Lyotropic liquid-crystalline (LLC), transition metal salt:oligo(ethylene oxide) nonionicsurfactant (CnH2n+1(CH2CH2O)mOH, denoted as CnEOm), systems have been studied by meansof diffraction, microscopy, and spectroscopy to elucidate the structural, thermal, andtemplating properties. In the system, the lyotropic salts of transition metal aqua complexes,such as chlorides and sulfates, are insoluble and do not form a LC phase in CnEOm-typenonionic surfactants. However, the transition metal aqua complexes of nitrates andperchlorates are soluble and form 2D and 3D hexagonal and cubic mesophases. These phasesare stable in a very broad range of salt:surfactant mole ratios (1.0 and 3.6). The nitratesalts form a hexagonal mesophase. However, in high nitrate salt concentrations (above 3.2salt:surfactant mole ratio), the salt crystals are either insoluble or the salt:surfactantmixtures are in a cubic mesophase. The structure and thermal properties of the new systemare determined by the solubility of the transition metal salts, the concentration of the salt,and the surfactant type. The LC [Cd(H2O)4](NO3)2:C12EO10 mesophase has been reacted withH2S gas to produce solid mesostructured CdS (meso-CdS). The meso-CdS particles arespherical in morphology and are made up of hierarchical organization of 2-4-nm CdSparticles. The salt:surfactant LLC systems and the solid meso-CdS have been investigatedusing polarized optical microscopy, X-ray diffraction, Fourier transform infrared, Fouriertransform Raman, and UV-vis absorption spectroscopy, scanning electron microscopy, andtransmission electron microscopy.