Adsorption of N-Decyl-N,N,N-trimethylammonium Triflate (DeTATf), a Cationic Surfactant, on the Au(111) Electrode Surface

Abstract

The adsorption behavior of the cationic surfactant N-decyl-N,N,N-trimethylammonium triflate (DeTATf) on the Au(111) electrode surface was characterized using cyclic voltammetry, differential capacity, and chronocoulometry. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DeTATf has a multistate character. At low bulk DeTATf concentrations, the adsorption state is consistent with the formation of an adsorbed film of nearly flat molecules. At higher concentrations this film may represent a three-dimensional aggregated state. At negative potentials and charge densities close to 0 microC cm-2, the data suggest the formation of a film of tilted molecules oriented with the hydrocarbon tail toward the metal surface and the polar head toward the solution. A surprising result of this study is that DeTATf displays adsorption characteristics of a zwitterionic rather than a cationic surfactant. This behavior indicates that the adsorbed species is an ion pair.

Adsorption of a quaternary ammonium surfactant on Au(1 0 0)

“…The measured cmc of OTATf was 8.1 mM in 50 mM NaF. This is roughly twenty times larger than the cmc reported for decyltrimethylammonium triflate (DeTMATf) in 0.1 M NaF [13]. The larger cmc for the shorter chained surfactant is congruent with reported cmc values for different length alkyltrimethlyammonium chloride surfactants [31] and sulfobetaines [32].…”

“…In the absence of specific (non-electrostatic) interactions between the surfactant headgroup and the substrate the parameters that largely dictate the observed morphology of the adsorbed surfactant molecules include the hydrophobicity/ hydrophilicty of the solid surface, repulsion between the surfactant headgroups, interchain attractive forces, and the relative solvation energies of the hydrophobic tail and polar headgroup of the surfactant. In a series of contributions, Lipkowski and co-workers were able to demonstrate that the surface aggregation of anionic [10,11], zwitterionic [12], and cationic [13,14] surfactants on metal electrode surfaces could be controlled and adjusted by the applied electric potential. The combined results of this body of work have recently been reviewed [15].…”

Boundary lubrication by adsorption film

“…Actually, studies on the adsorption process of different interfaces have long been hampered by the need to discriminate between the few atoms at the interface, and the many more atoms that exist in the two bulk phases involved. A number of modern surface-sensitive techniques were developed in the late 20 th century to overcome this obstacle, such as AFM [31][32][33], electrochemistry [34], QCM [35−37], dual polarization interferometry (DPI) [38], and neutron reflectivity [39−41], to provide more information about SAMs on the solid surface both in air and in a liquid. A significant amount of useful knowledge has been acquired from these useful tools applied to SAMs, such as the physical and chemical properties of the molecules, the film thickness, the adsorbed mass, the aggregation structure, and the interactions between the molecules and between the molecules and solid surface.…”

Stick–Slip Friction of Stainless Steel in Sodium Dodecyl Sulfate Aqueous Solution in the Boundary Lubrication Regime

“…There have been a lot of investigations on the details of the adsorption process and adsorption structures of surfactants at solid/liquid interfaces [29][30][31][32][33][34][35][36][37][38][39][40]. Adsorption isotherm is the most widely used traditional method to provide evidence for surfactant aggregation, and the structure is interpreted with regard to the measured surface excess or adsorbed mass [32].…”

“…Adsorption isotherm is the most widely used traditional method to provide evidence for surfactant aggregation, and the structure is interpreted with regard to the measured surface excess or adsorbed mass [32]. In the recent two decades, many new experimental techniques including atomic force microscopy (AFM) [33,34,41], electrochemistry [35], quartz crystal microbalance (QCM) [36][37][38], dual polarization interferometry (DPI) [39] and neutron reflectivity [40] have been employed to provide more information about the surfactant adsorption. The high resolution in nanogram of QCM measurement allows a precise monitoring of the adsorbed mass, which provides a more accurate method to obtain the adsorption isotherm than the traditional depletion method.…”