Adsorption behaviors of branched cationic Gemini surfactants and wettability in quartz-solution-air systems
The adsorption and wetting on quartz surface from aqueous solutions of xylyl-substituted biquaternary ammonium salt Gemini surfactants with different spacer (C3 and C6) have been investigated. The interfacial properties of surfactant solution such as contact angle, adhesional tension ( ), quartz-water interfacial tension ( ) as well as adhesion work (WA) have been estimated. The obtained results show that C3 and C6 have similar adsorption behavior at quartz surface. Before critical micelle concentration (cmc), the contact angles of Gemini surfactants slowly increase with the increasing concentration and the adsorption amounts at water-air interface are almost the same as those at quartz-water interface. After cmc, the Gemini surfactant Cn molecules form a more compact adsorption film through bending the flexible spacer chain, instead of the formation of bi-layer. As a result, a further increase in quartz-liquid interfacial tension ( ) and a consequent increase in contact angle have been observed after cmc. Gemini C6 shows stronger ability of hydrophobic modification for quartz surface than C3, demonstrating contribution of longer methylene spacer to the hydrophobic modification of quartz surface.