Interparticle distance between the sheet-like niobate particles in the lamellar-forming colloidal dispersion

Yamaguchi, Daisuke; Miyamoto, Nobuyoshi*; Fujita, Takako*; Nakato, Teruyuki*; Koizumi, Satoshi; Ota, Noboru*; Yagi, Naoto*; Hashimoto, Takeji

The lyotropic lamellar phase in colloidal suspension has been well established in the recent work of the exfoliated inorganic phosphatoantimonate crystal. Here we report the other distinct lamellar phase formed in the colloidal suspension of hexaniobate "nanosheet", which is coexistent with an isotropic phase. This colloidal system clearly shows that not only the degree of orientational order but also that of positional order are quite different between upper isotropic phase and bottom lamellar phase. However, a definite interparticle correlation does exist in the isotropic phase and the difference in the mean interparticle distance (d) between lamellar and isotropic phases turned out rather small. All those pieces of experimental evidence suggest that the coexisting isotropic-lamellar phases is not attributed to the sedimentation of the nanosheet particles by the gravity but arisen as a result of ordering process of nanosheet particles by getting over the random thermal force of Brownian motion.