Oxypropylene chain length affects the physicochemical properties of ortho ester-based gemini surfactants

In this study, we synthesized ortho ester-based surfactants, with oxypropylene chain lengths from 1 to 3000, from a short-chain ortho ester, propylene glycol, and polyoxyethylene stearyl ether. We subsequently reacted these ortho ester surfactants with propylene glycol as a spacer to yield gemini surfactants. We characterized the surface activities of each of these gemini surfactants in terms of its critical micelle concentration (CMC), surface excess concentration (ΓCMC), surface area demand per molecule (ACMC), surface tension at the CMC (γCMC), and standard free energy of micellization per mole of monomer unit (ΔGm). Increasing the oxypropylene chain length had a significant influence on the surface activity. Overall, these ortho ester-based gemini surfactants possess excellent surface properties, providing low contact angles and emulsion stability.