Surface Properties of Gleditsia Saponin and Synergisms of Its Binary System

Abstract

A gleditsia saponin (GS) is isolated and purified from the fruits of Gleditsia sinensis Lam. Its surface and thermodynamic properties in aqueous solution at 0, 15, 25, 35, 45, and 60°C have been investigated by surface tension measurement. The major data at 25°C are the critical micelle concentration (cmc), 1.10E‐3 mol · L−1; the surface tension at cmc (γ cmc ), 34.4 mN · m−1; the maximum surface excess concentration (Γmax), 2.33E‐6 mol · m2; the minimum area per molecule (A cmc ), 0.712 nm2; the standard adsorption energy (ΔG ad 0), −32.9 kJ · mol−1; and the standard micellization energy (ΔG m 0), −16.9 kJ · mol−1. The molecular interaction parameters, β s and β m , for the binary systems of GS with a cationic surfactant (C16H33NMe3Br), an anionic surfactant (C12H25SO3Na), and a nonionic surfactant (C8H17Ph(EO)10OH) have been determined. Based on the regular solution treatments of Rubingh, Rosen, and their coworkers, the conditions of synergism in surface tension reduction effectiveness have been extended. The condition to produce this synergism and the corresponding parameters at the maximum synergism point, i.e., the mole fractions of surfactant 1 in the solution phase (α1*), the critical micelle concentration of mixtures (cmc 12*), and the surface tension at this concentration (γ cmc12*), are given. The results show that of the three binary systems, synergism in micelle formation can occur only in the mixture of GS with cationic surfactants; synergism in surface tension reduction efficiency can occur in the mixture of GS with both cationic surfactant and nonionic surfactants, but, all the binary systems of GS with ionic and nonionic surfactants can show remarkable synergism in surface tension reduction effectiveness.