Phase separation in the system with sodium silicate and sodium dodecyl sulfate under acidic conditions

Abstract

Phase separation in an acidic aqueous solution with sodium silicate and sodium dodecyl sulfate (SDS) was investigated. The solution separated into silica-rich and SDS-rich phases during condensation of silica components. During the phase separation, the transition structure was fixed by gelation, resulting in mutually continuous morphology. The addition of a small amount of water-miscible organic solvents, such as methanol, ethanol, 1-propanol, and 1-butanol, into the reacting solution greatly decreases both viscosity and phase separation tendency of the solution. In the system with high concentration of strong acid, SDS molecules form wormlike micelles, which not only increase viscosity of the solution but also play an important role in the phase separation in the solution because the formation of wormlike micelles increases apparent molecular weight of SDS and decreases mixing entropy. The decrease in the viscosity by the addition of organic solvents suggests that wormlike micelles become small in the presence of organic solvent molecules. Consequently, the addition of appropriate amount of organic solvent is effective for controlling phase separation tendency and size of the resulted macropores in the system with SDS through the change in the structure of the micelles.