Infrared Studies of the Potential Controlled Adsorption of Sodium Dodecyl Sulfate at the Au(111) Electrode Surface

Abstract

Quantitative subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was used to determine the conformation and orientation of sodium dodecyl sulfate (SDS) molecules adsorbed at the single crystal Au(111) surface. The SDS molecules form a hemimicellar/hemicylindrical (phase I) structure for the range of potentials between -200 ≤ E < 450 mV and condensed (phase II) film for electrode potentials ≥500 mV vs Ag/AgCl. The SNIFTIRS measurements indicate that the alkyl chains within the two adsorbed states of SDS film are in the liquid-crystalline state rather than the gel state. However, the sulfate headgroup is in an oriented state in phase I and is disordered in phase II. The newly acquired SNIFTIR spectroscopy measurements were coupled with previous electrochemical, atomic force microscopy, and neutron reflectivity data to improve the current existing models of the SDS film adsorbed on the Au(111) surface. The IR data support the existence of a hemicylindrical film for SDS molecules adsorbed at the Au(111) surface in phase I and suggest that the structure of the condensed film in phase II can be more accurately modeled by a disordered bilayer.

Redox-Controlled Ion-Pairing Association of Anionic Surfactant to Ferrocene-Terminated Self-Assembled Monolayers

“…Depending on the charge density of the solid surface, its hydrophobicity/ hydrophilicity, and the concentration in aqueous solution, NaC 12 SO 4 adopts different structures at the solid/aqueous solution interface (Scheme 2). More specifically, hemicylindrical stripes, 1,19 a smooth liquid-crystalline bilayer, 1,21,43 or distorted surfactant aggregates 19 have been observed by AFM. The surfactant anion coverages measured by SPR do not support an adsorbed bilayer of C n SO 4 − .…”

Effect of Imidazolium Ionic Liquid Additives on Lubrication Performance of Propylene Carbonate under Different Electrical Potentials

“…In the present work, we study tribological performance of three imidazolium IL additives, 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm]BF 4 ), 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIm]PF 6 ) and 1-decyl-3-methylimidazolium hexafluorophosphate ([DMIm]PF 6 ), in ester propylene carbonate (PC) base lubricant under different electrical potentials. As shown in previous investigations, the electrical potential plays an important role in ionic surfactant adsorption on metal surfaces in liquids [14][15][16] and thus has an impact on the boundary lubrication in water or PC environment [10,17,18]. The purpose of this study was to investigate the synergetic effect of imidazolium ILs and electrical potential on the lubricity of the ester PC.…”

Boundary lubrication by adsorption film

“…The materials usually used in studies on nanotribology include mica [86] and graphite [74], which have large areas with an atomically smooth surface that can be achieved by peeling as a result of the special layered structure of the materials, and silicon and silicon-based materials such as silica [15], which are acquired by polishing a silicon surface to an atomic smoothness and related post-treatment process. Gold, which is an inert metal, can be flattened, either by annealing [87] or sputtering/ evaporating [33], on an atomically smooth surface. Other metals such as steel [23] can be highly polished, and are thus candidates in these types of studies.…”