Effect of zwitterionic surfactants on wetting of quartz surfaces

Advancing contact angle (theta), for aqueous solutions of the zwitterionic surfactants, hexadecanol glycidyl ether glycine Betaine (C16PB), guerbet alcohol hexadecyl glycidyl ether glycine Betaine (C(16)GPB), hexadecanol polyoxyethylene(3) glycidyl ether glycine Betaine (C-16(EO)(3)PB) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether glycine Betaine (C(16)G(EO)(3)PB), were measured on the quartz surface by the sessile drop analysis. The atomic force microscope (AFM) has been used to detect the nature of adsorption film at quartz surface. The obtained results indicate there are only slightly changes of contact angle as a function of bulk concentration for four surfactants during the experimental concentration range caused by the random arrangement of surfactant molecules at quartz surface through Lifshitz-van der Waals interactions. For C16PB and C(16)GPB, a similar adsorption density at water-air and quartz-water interface is observed. In the case of C-16(EO)(3)PB and C(16)G(EO)(3)PB solutions, a smaller surfactants adsorption at quartz-water interface than at water-air interface probably results from steric effect due to parallel orientation of surfactants in the monolayer at quartz-water interface resulted from the interaction between EO group and quartz. The adsorption characteristics of zwitterionic surfactants remain less variation with the insertion of EO group and the presences of branched-chain in the hydrophobic group are quite opposite. For C16PB and C-16(EO)(3)PB, a three-stage adsorption mechanism has been provided, while a four-stage mechanism must be taken into account for C-16 G PB and C(16)G(EO)(3)PB. The characteristics of force curves measured by AFM between alkyl-modification tips and surfactant-modification quartz plates can strongly confirm the nature of modified film on quartz surface and ensure the adsorption mechanism provided above. (C) 2013 Elsevier B.V. All rights reserved.