Alkyl-Based Surfactants at a Liquid Mercury Surface: Computer Simulation of Structure, Self-Assembly, and Phase Behavior

Abstract

Self-assembled organic films on liquid metals feature a very rich phase behavior, which qualitatively differs from the one on crystalline metals. In contrast to conventional crystalline supports, self-assembled alkylthiol monolayers on liquid metals possess a considerably higher degree of molecular order, thus enabling much more robust metal-molecule-semiconductor couplings for organic electronics applications. Yet, compared to crystalline substrates, the self-assembly of organic surfactants on liquid metals has been studied to a much lesser extent. In this Letter we report the first of its kind molecular simulation investigation of alkyl-based surfactants on a liquid mercury surface. The focus of our investigation is the surfactant conformations as a function of surface coverage and surfactant type. First, we consider normal alkanes because these systems set the basis for simulations of all other organic surfactants on liquid mercury. Subsequently, we proceed with the discussion of alkylthiols that are the most frequently used surfactants in the surface science of hybrid organometallic interfaces. Our results indicate a layering transition of normal alkanes as well as alkylthiols from an essentially bare substrate to a completely filled monolayer of laying molecules. As the surface coverage increases further, we observe a partial wetting of the laying monolayer by the bulk phase of alkanes. In the case of alkylthiols, we clearly see the coexistence of molecules in laying-down and standing-up conformations, in which the sulfur headgroups of the thiols are chemically bound to mercury. In the standing-up phase, the headgroups form an oblique lattice. For the first time we were able to explicitly characterize the molecular-scale structure and transitions between phases of alkyl-based surfactants and to demonstrate how the presence of a thiol headgroup qualitatively changes the phase equilibrium and structure in these systems. The observed phenomena are consistent with available direct and indirect experimental evidence.

Computer Simulation And Modeling The Metal To Insulating Transition Of Liquid Mercury Via Pair, Empirical And Many-Body Potentials

“…However, the conclusion of all these deferent methods, theoretical or practical, confirmed that the M-NM transition occurred at density nearness 9 g/cm 3 . In the vicinity of this thermodynamic state the transition appeared within the alteration of aforesaid properties.…”

“…Mercury metal (Hg) is unique elemental which is liquid at room temperature. In spite of controversy about its poisonous, toady mercury due to dissolves nearly all metals, is used in a variety of industrial application such; mercury in medicine and industry i.e., dental amalgam [1], energy production [2], utilization mercury self-assembled monolayers (SAMs) as semiconductor device [2,3], liquid Hg as a base for Langmuir films of imidazolium-based ionic liquids for electrochemical applications [4]. On other hand, the technology development of removal and capture of mercury as contamination is one of vital environmental issue in the recent years, which has widely probed by both experiments and simulations studies [5,6,7,8,9].…”

Computer simulation and analysis of self-assembled alkylthiol monolayers on the surface of liquid mercury

“…The simulations presented in the current chapter allow for the first time to directly access the molecular-scale structure of the self-assembled alkylthiol monolayers on the surface of liquid mercury and to understand factors that influence it. Most of the results on the equilibrium structure of the thiol SAMs from this chapter the reader can also find in my recent publication [156].…”

“…Refs. [77,156,159,160]), which has a very flexible functional form The non-bonded interaction describes intermolecular interactions, such as Van der Waals and metallic (for bulk Hg) interactions, and is given by…”

“…The U Hg−CH 2 and U Hg−CH 3 interactions follow the same functional form as Eq. 4.10 and were parametrized to yield an experimental adsorption energy of 5.4 kJ/mol per alkyl group on liquid mercury [156]. The values of respective parameters from Eq.…”