Liquid crystalline colloidal system obtained by mixing niobate and aluminosilicate nanosheets: A spectroscopic study using a probe dye

A novel colloidal system composed of two kinds of inorganic oxide nanosheets dispersed in water was prepared by mixing exfoliated layered niobate K4Nb6O17 and montmorillonite clay. According to the observation of the colloids under crossed polarizers, the obtained niobate-clay colloids were liquid crystalline with apparently homogeneous macroscopic ordering, similar to the previously reported single-component colloids of the exfoliated niobate layers. X-ray diffraction measurements of the dried colloids indicated that the niobate-clay colloids were regarded as mixtures of the niobate and clay microphases: the colloids are microscopically demixed. Spectroscopic investigations using a cationic cyanine dye as a probe showed that the dye was selectively adsorbed on the clay platelets; the results indicated mass transfer of the dye molecules from the niobate nanosheets to clay platelets, and the transfer was accompanied by alterations of the aggregation state of the probe dye. The microenvironments provided by the clay nanosheets were the same as those given by the single-component clay colloids. Polarized spectra of the dye-adsorbed niobate-clay colloids demonstrated that the clay nanosheets were present in the isotropic state among the niobate nanosheets, which were orientationally ordered to give liquid crystallinity of the colloids.