Lyotropic Liquid-Crystalline Phase of Oligo(ethylene oxide) Surfactant/Transition Metal Salt and the Synthesis of Mesostructured Cadmium Sulfide

Abstract

Lyotropic liquid-crystalline (LLC), transition metal salt:oligo(ethylene oxide) nonionic surfactant (C n H 2 n +1 (CH 2 CH 2 O) m OH, denoted as C n EO m ), systems have been studied by means of diffraction, microscopy, and spectroscopy to elucidate the structural, thermal, and templating 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 C n EO m -type nonionic surfactants. However, the transition metal aqua complexes of nitrates and perchlorates are soluble and form 2D and 3D hexagonal and cubic mesophases. These phases are stable in a very broad range of salt:surfactant mole ratios (1.0 and 3.6). The nitrate salts form a hexagonal mesophase. However, in high nitrate salt concentrations (above 3.2 salt:surfactant mole ratio), the salt crystals are either insoluble or the salt:surfactant mixtures are in a cubic mesophase. The structure and thermal properties of the new system are determined by the solubility of the transition metal salts, the concentration of the salt, and the surfactant type. The LC [Cd(H 2 O) 4 ](NO 3 ) 2:C 12 EO 10 mesophase has been reacted with H 2 S gas to produce solid mesostructured CdS (meso-CdS). The meso-CdS particles are spherical in morphology and are made up of hierarchical organization of 2−4-nm CdS particles. The salt:surfactant LLC systems and the solid meso-CdS have been investigated using polarized optical microscopy, X-ray diffraction, Fourier transform infrared, Fourier transform Raman, and UV−vis absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy.