Alkanethiol mixed layers

In mixed monolayers with unsubstituted alkanethiols, containing up to 50% of the hydroxyalkanethiol, there is no indication of such H-bond formation. This is inconsistent with the phase-separation hypothesis, as hydroxy functions would surely form H-bonds with each other in domains, and Bertilsson and Liedberg concluded that the monolayers do not phase-segregate246. On the other hand, mixed layers of alkanethiols of different chain lengths showed, however, that these layers are at least partially crystalline, while disorder was expected for homogeneous monolayers. Existence of at least partial phase-separation was inferred161. 

SvobodovS, L., SnejdSrkovd, M., T6th, K., Gyurcsanyi, R. E., Hianik, T. (2004). Properties of mixed alkanethiol-dendrimer layers and their applications in biosensing. Bioelectrochemistry 63, 285-289. 

H. Tokuhisa, M. Zhao, L.A. Baker, V.T. Phan, D.L. Dermody, M.E. Garcia, R.R. Peez, R.M. Crooks, T.M. Mayer, Preparation and Characterization of Dendrimer Mono-layers and Dendrimer-Alkanethiol Mixed Monolayers Adsorbed to Gold, Journal of the American Catalysis Society 120, 4492, 1998. 

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]. 

The ion-pair theory was invoked by Dong and coworkers to explain the behavior of adsorption of various surfactants at coassanbled Fc-teminated alkanethiol-alkylth-iolphene thiol SAMs on gold [51]. It was proposed that the adsorption of surfactants at the mixed monolayer created an energy barrier that inhibited the diffusion of counter ions present in solution from diffusing into the adsorbed layer as compensation for the oxidation of the Fc to Fc ions [51]. The creation of a barrier at an interface can be tested with electrochanical impedance spectroscopy (EIS) where an increase... 

Gupta P, Ulman A, Fanfan F, Korniakov A, Loos K. (2005) Mixed self-assembled mono-layer of alkanethiolates on ultrasmooth gold do not exhibit contact angle hysteiesis./A Chem Soc 127 4-5. 

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