Thiol adsorption

Fig. 6 Schematic representation of the mechanism of thiol adsorption on different metal surfaces [102].

Currently, we are studying in our group the adsorption of polyelectrolytes from aqueous solutions on charged and uncharged surfaces. Investigations of thiol adsorption on surfaces (e.g., Ref 257, 258) conformational equilibria of polymers near surfaces (e.g.. Ref 259), of surfactants with surfaces and micelles [260-263] and others were mostly done without explicit modeling of the solvent. 

Mercury offers an ideal, atomically flat liquid metal surface with no preparation needed and with high affinity for thiol adsorption. SAMs on mercury surfaces are notable for the absence of defects, compact structure, and high reproducibility. One possibility is to use a homemade hanging mercury drop electrode (HMDE), which can be immersed in a thiol solution or passed through a layer of thiols floating on the electrolyte [168-171]. A static mercury... 

STM measurements were carried out with a Hg sessile drop before and after thiol adsorption, which involve a complex drop flow system allowing control of the drop size and flattening of the drop surface [174]. Compression of the Hg drop to a flat shape allowed STM images to be obtained. 

ToF-SIMS is routinely applied to the characterization of competitive thiol adsorption and mixed self-assembled layers [73-75]. Mixed monolayers of alkyl sulfides (and dialkyl disulfides) were first investigated with SIMS by Offord et al. in a detailed multitechnique study [76]. The authors concluded that the adsorption is thermodynamically driven for sulfides (longer chains preferred) and kinetically driven for disulfides (no preference). In parallel, the usefulness of ToF-SIMS to determine the chemical structure and composition of mixed layers of alkanethiols was demonstrated [77]. 

Whereas the film is finished to 95% within 10 s at potentials of -400 to +200 mV, yielding a film composed of domains with a lateral size of 10-20 nm, it takes thousands of seconds at very cathodic potentials for the domains to cover the surface, but the domains are much larger. A detailed analysis shows that the thiol adsorption is at least a two-step process physisorption followed by chemisorption [53a] ... 

Figure 3 If the capacity of the gold surface is measured during thiol adsorption, a decrease in capacitance can be observed due to the pushing apart of the double layer by the adsorbing thiol.

Cohen-Atiya M, Mandler D (2003) Studying thiol adsorption on An, Ag and Hg surfaces by potentiometric measurements. J Electroanal Chem 550-551 267-276... 

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