Effect of zwitterionic surfactants on wetting of quartz surfaces

• There are only slightly changes of contact angle as a function of Zwitterionic surfactant concentrations.
• The branched-chain appears to cause more obvious increase in the contact angle of surfactant solution.
• The values of adhesional tensions of zwitterionic saturated monolayers are higher than those of cationic surfactants.
• The random arrangement of zwitterionic molecules at quartz surface can be detected by AFM.

Advancing contact angle (θ), for aqueous solutions of the zwitterionic surfactants, hexadecanol glycidyl ether glycine Betaine (C16PB), guerbet alcohol hexadecyl glycidyl ether glycine Betaine (C16GPB), hexadecanol polyoxyethylene(3) glycidyl ether glycine Betaine (C16(EO)3PB) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether glycine Betaine (C16G(EO)3PB), 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 C16GPB, a similar adsorption density at water–air and quartz–water interface is observed. In the case of C16(EO)3PB and C16G(EO)3PB 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 C16(EO)3PB, a three-stage adsorption mechanism has been provided, while a four-stage mechanism must be taken into account for C16 G PB and C16G(EO)3PB. 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.

The random arrangement of surfactant molecules at quartz surface results in slightly change of contact angle as a function of concentration.Figure optionsDownload as PowerPoint slide