Role of isomers and steric hindrance in the micellization of carboxylated carbosilane surfactants

Abstract

Abstract A series of carboxylated carbosilane surfactants with methyl, ethyl, branching CH3-, phenyl, and cyclohexyl (Me-Si2C-COONa, Et-Si2C-COONa, Si2C-La-COONa, Ph-Si2C-COONa, and Cy-Si2C-COONa) were prepared. The effect of isomer and steric hindrance on their micellization in aqueous solution was investigated by surface tension, conductivity, transmission electron microscopy (TEM) and dynamic light scattering (DLS). Si2C-La-COONa with branching CH3- shows a lower γCMC value and higher the CMC value compared with Et-Si2C-COONa. Cy-Si2C-COONa with cyclohexyl (41.6 mN·m− 1) and Ph-Si2C-COONa with phenyl (43.9 mN·m− 1) have larger γCMC values due to the distinct steric hindrance and hydrophobicity. In aqueous solution, the aggregation behavior of Si2C-La-COONa, Cy-Si2C-COONa, and Ph-Si2C-COONa is enthalpy-driven. However, the micellization process of Me-Si2C-COONa and Et-Si2C-COONa is governed by the enthalpy-driven at high temperature and entropy-driven at low temperature. DLS and TEM results indicate that the carboxylated carbosilane surfactants can self-assemble into aggregate with hydrodynamic diameters of 50–400 nm.