Synthesis and properties of stellate lactosamide quaternary ammonium surfactants

Abstract

A number of stellate lactosamide quaternary ammonium salt surfactants (N-dodecyl-N, N-bis[(3-lactosamide) propyl]-N-alkylamine bromide, C n DBLB, where n represents hydrocarbon chain lengths of 12,14 and 16) was successfully synthesized from lactobionic acid, N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine, and bromoalkane by a two-step method comprising a proamine ester reaction and post-quaternization. The surface activity, adsorption, and aggregation behavior of the surfactants in aqueous solutions were investigated by dynamic/static surface tension, contact angle, dynamic light scattering, proton nuclear magnetic resonance spectroscopy, and transmission electron microscopy measurements. The results demonstrated that the equilibrium surface tension ( γ cmc ) of the C n DBLB surfactant was in the range of 28–35 mN/m; thus, it had a strong ability to reduce the surface tension of water. Furthermore, with increase in the carbon chain length of the surfactant, the saturated adsorption amount (Г max ) increased while A min decreased. However, the adsorption duration of C n DBLB was long, and rapid equilibrium could not be achieved on the surface of the solution, indicating a mixed kinetic adsorption mechanism. All three surfactants formed spherical micelles in aqueous solutions. Because the hydrophobic carbon chain length increased, the molecular structure complexity, steric hindrance, and hydrophobic group–water interaction (repulsion) increased, accounting for the unique aggregation behavior of C n DBLB in aqueous solutions. With increase in the concentration of the C 12 DBLB surfactant, the size of the aggregates formed increased. The sizes of the C 14 DBLB and C 16 DBLB aggregates increased initially, decreased, and subsequently increased again. Moreover, the morphology of molecular self-assembly was discussed. C n DBLB surfactant at low concentration was low toxicity or non-toxic, with the increase of concentration, its toxicity will also increase.