The spot method has been conventionally used to measure the amount of methylene blue (MB) adsorbed on bentonite, which mainly consists of smectite. In this method, MB solution is added stepwise to the bentonite dispersion, and a drop of the MB solution and bentonite is placed on a filter paper to form a dark blue spot each time MB is added. When a sufficient amount of MB was added, a light blue halo appeared around each spot. It is assumed that when the halo appeared, the amount of MB adsorbed onto bentonite is equal to the amount of MB added to the bentonite dispersion. However, the appearance of the halo indicates the presence of unadsorbed MB. Herein we measured the concentration of unadsorbed MB using the spectrophotometry and obtained the “true value” of the amount of MB adsorbed on bentonite when the halo appeared.

When an excess amount of MB was added to the bentonite, the amount of MB adsorbed on bentonite was smaller than the amount added. This indicated that only a part of the added MB was adsorbed on bentonite, and some unadsorbed MB remained. When the amount of MB within the adsorption capacity was added, the amount of MB adsorbed was equal to the amount of MB added and the width of the halo was smaller than approximately 0.5–1.0 mm, regardless of bentonite properties. Thus, the spot method gives the true value of the amount of MB adsorbed when the width of the halo is smaller than approximately 0.5–1.0 mm.

Inorganic nanosheets obtained by exfoliation of layered crystals such as smectite-type clays have been actively investigated as building blocks of nanomaterials in the past 25 years. However, their colloidal systems were at the outside of such a research trend. At the beginning of 21st century, liquid crystalline behavior of colloidal nanosheets was recalled into academic studies, and then the materials chemistry of ‘nanosheet liquid crystals’ has been gradually developed. Many popular nanosheets have been registered at the library of liquid crystals. Nanosheet liquid crystals are rare examples of inorganic soft materials, whose properties are greatly different from their mother crystals due to their softness. A typical property of nanosheet liquid crystals is structural coloration reflecting long periodic lengths between nanosheets. Also, technical inventory of manipulating liquid crystalline nanosheets has been enriched as exemplified by electric alignment and optical manipulation. Hierarchical structures of liquid crystalline nanosheets up to mm-level lengths have been organized with appropriate combination of manipulating techniques.