Anomalous gelation of self-assembling ethanol molecules

A low-molecular-weight gel is one that is organized by small molecules via noncovalent bonds, and some low-molecular-weight gels already being used in our daily lives. In general, the mechanism of formation of low-molecular-weight gels involves the gelation of solvents such as ethanol and water in the presence of low-molecular-weight gelators, which have larger molecular weights than the solvents. The gelator creates a supramolecular network via noncovalent bonds, and this network holds the solvent molecules, causing them to lose fluidity and thereby promoting gelation. That is, low-molecular-weight gels do not self-assemble and gelate solvent molecules themselves; the literature contains no reports of the self-assembly and gelation of extremely small solvent molecules such as ethanol and water. However, in this work, we found that ethanol molecules themselves form a large gel structure by self-assembling with few-nanometer-diameter oxide nanoparticles and water molecules. Our finding reveals an intriguing phenomenon where ethanol molecules support the main structure of a large gel structure through supramolecular assembly via hydrogen bonding. The key factor for the gelation of ethanol observed in this study is the presence of BaZrO3 nanoparticles, which are positively charged and homogeneously dispersed. When these nanoparticles and water were present, we observed the gelation of a substantial amount of ethanol, which would not normally occur. Our results overturn the common belief that extremely small molecules such as ethanol cannot function as a main bearer of gelatinization, and our discovery opens a path to the development of a novel self-assembly system that has not been previously reported. In addition, because the method proposed in the present work can potentially be used to prepare gels that incorporate other extremely small molecules having hydrogen bonds, we expect our findings to lead to the development of various novel materials with unique functions.