Potential-dependent wetting of octadecanethiol-modified polycrystalline gold electrodes

• Published in: Langmuir 1992-10, Vol.8 (10), p.2560-2566
• Main Authors: Sondag-Huethorst, J. A. M, Fokkink, L. G. J
• Format: Article
• Language: English
• Subjects: Adsorption; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Study of interfaces
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la00046a033

A Wilhelmy plate technique is used to characterize the potential-dependent wetting of octadecanethiol (C sub(18)H sub(37)SH)-modified polycrystalline gold electrodes in 10 super(-2) M K sub(2)SO sub(4). This technique is relatively simple and provides information on the electrostatic component of the solid electrode/solution interfacial tension ( Delta gamma sub(SL)(E)) and the electrocapillary maximum (ecm). Wetting measurements are carried out simultaneously with differential capacitance measurements and cyclovoltammetry. In the potential range where only double-layer charging occurs, the adsorbed, self-assembled C sub(18)H sub(37)SH layer is found to be very stable. The extreme hydrophobicity, the low differential capacitance (approximately 0.7 mu F cm super(-2)), and the low double-layer current (a factor of 100 less than for clean gold) are all indicative of the insulating dielectric character of these monolayers. By scanning from the ecm at about -0.45 V (SCE) to +0.8 V (SCE), the advancing contact angle decreases from 116 degree to 110 degree , corresponding to a decrease in gamma sub(SL) of 7 mN m super(-1). The observed relationship between Delta gamma sub(SL) and E can be conveniently described by interfacial thermodynamics.