Structure of stable double‐ionic model water clusters of quaternary alkylammonium surfactants with some monovalent counterions as derived by the DFT method

Abstract

AbstractWe have performed DFT calculations on stability of model water clusters of alkylammonium surfactants with different monovalent counterions, such as fluoride, chloride, bromide, hydroxide, nitrate, perchlorate, and tetrafluoroborate. We have found that stable water clusters are formed if they contain at least three molecules of water. We can distinguish two types of stable water clusters of ammonium salts: stable neutral water clusters and double‐ionic water clusters. According to the results of our DFT calculations, the first type of cluster is more stable by ca. 3–7 kcal/mol. We have found several types of stable double‐ionic water clusters of alkylammonium salts with different counterions. In each case, the stable structures have some element of symmetry and they are stabilized by hydrogen bonding. The computed energy of double‐ionic cluster formation of hydrated alkylammonium salts with different counterions correlates quite well with experimental data of the critical micelle concentration (CMC), indicating a role of hydration phenomena in the process of micelle formation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004