Molecular Dynamics Simulation of Alkylthiol Self-Assembled Monolayers on Liquid Mercury

Яковлев, А. В.; Bedrov, Dmitry; Müller, Marcus

doi:10.1021/acs.langmuir.6b03774

Cited by 8 publications

(8 citation statements)

References 59 publications

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“…[26] However, surfactants only bring about modest changes in interfacial tension in liquid metals. For example, adding an alkythiol monolayer to Hg in the vapor phase lowers the surface tension by %60 mN m À1 , similar in magnitude to what surfactants do for water, [27,28] but here accounting for only a 10% change relative to the large surface tension of clean Hg. Polymers, such as polyvinyl alcohol, have been used on gallium-based alloys to help stabilize colloidal suspensions.…”

supporting

confidence: 52%

Interfacial Tension Modulation of Liquid Metal via Electrochemical Oxidation

Song

Daniels

Kiani

et al. 2021

Advanced Intelligent Systems

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Among all of the elements in the periodic table, there are only five metals that are liquid near room temperature: francium (Fr), cesium (Cs), rubidium (Rb), mercury (Hg), and gallium (Ga).The first three elements, however, are not practical for applications because they are either radioactive (Fr, Cs) or explosively reactive with air (Rb). Mercury was widely used in the past but is now avoided due to its toxicity. [1,2] By process of elimination, therefore, gallium and gallium-based alloys are the safest liquid metals at or near room temperature. [3] Gallium, discovered in 1875, has an extremely low vapor pressure even at high temperatures (effectively zero at room temperature and only 1 kPa at 1037 C; [4] by comparison, water has a vapor pressure of 1 kPa at 7 C). This low vapor pressure keeps the liquid from evaporating and eliminates the danger of vapor inhalation. While gallium should be found as solid at room temperature, because its melting point is 30 C, it is often liquid due to its ability to supercool. To assure a roomtemperature liquid phase, eutectic alloys containing at least one additional metal are commonly used to lower the melting point below room temperature. Two popular commercial alloys are Galinstan (68.5 wt% Ga, 21.5 wt% In, and 10.0 wt% Sn) and eutectic gallium indium (EGaIn, 75.5 wt% Ga and 24.5 wt% In), for which the melting point is 10.7 and 15.5 C, respectively. [5] In air, these alloys all form surface oxides within microseconds due to a high reactivity of gallium with oxygen. Because Ga oxidizes more readily than other components in these alloys, the surface oxides are dominated by gallium oxide species. These alloys thereby exhibit similar interfacial behavior to gallium in air. [6] Thus, we discuss these gallium-based alloys without distinguishing them by their bulk composition, except where warranted. Interfacial Tension ModulationMetals have significantly larger surface tension (>400 mN m À1 depending on the liquid metal [7] ) than common fluids such as water (72 mN m À1 ), as shown in Figure 1a. The large surface tension of metals is due to the metallic bonds. [4] Gallium is notable for having the highest surface tension (708 mN m À1 ) of any liquid in air near room temperature [8,9] and alloys of Ga, such as EGaIn, also have enormous surface tension (624 mN m À1 ). [10] We note the term "surface tension" refers to the tension of fluid interfaces in contact only with a vapor phase, whereas "interfacial tension" refers more broadly to the tension of fluids

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supporting

confidence: 52%

Interfacial Tension Modulation of Liquid Metal via Electrochemical Oxidation

Song

Daniels

Kiani

et al. 2021

Advanced Intelligent Systems

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“…This is the first time that peptide structural dynamics are shown at Hg‐surfaces with applied external electric field. The results presented here extend the previously published MD findings on the structural dynamics of amino acids and peptides at a Hg‐surface, as was shown for His interactions and for alkylthiol self‐assembled monolayer (SAM) formation .…”

Section: Introductionmentioning

confidence: 99%

Structures of Peptidic H‐wires at Mercury Surface: Molecular Dynamics Study

et al. 2019

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Biopolymer immobilization strategies, self‐assembly systems and adsorption phenomenon in general are crucial for the development of methods that work on the basis of the surface‐detection principle, including electrochemistry. A mechanistic view into the interaction of biopolymers with electrode surfaces is also important for studying fundamental and dynamic processes such as electron/proton transport. In this sense, the utilization of new approaches for investigating the interfacial behavior of immobilized biomolecular architectures is a permanent focus. Here we use a molecular dynamics (MD) approach to simulate the structural changes and metallic surface interactions of a model 21‐mer peptide of His (H) and Ala (A), A3(HA2)6, a peptidic proton wire (H‐wire). This H‐wire was previously proposed for the electrochemical study of proton transfer at mercury electrodes (Langmuir, 2018, 34, 6997). The rigid solid mercury mono‐atomic layer (α‐mercury lattice model) was used systematically in all our simulations. The calculations were performed in a simulation box with 1, 16 and 32 H‐wire strands attached covalently to the mercury layer via the thiol group of a cysteinamide residue appended to the H‐wire C‐terminus. The internal alpha‐helical configuration of H‐wires was maintained by the presence of 2,2,2‐trifluoroethanol. It was shown that both the surface density of H‐wires and the protonation state of His residues play a decisive role in the structural stability and orientation of the peptide to the surface, whereas the applied voltage only has a mild effect on it, especially in case of 16 and 32 H‐wire strand configurations. The MD simulations presented here could be used for the further investigation of other peptides at metallic surfaces and for electrochemical analyses of structural changes of surface‐attached peptides that depend on their protonation states and other external factors.

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“…The nonbond van der Waals interaction is expressed by a 12–6 Lennard-Jones (LJ) potential To maintain the consistency of calculations with regard to the components of the surface, the LJ parameters for unlike atoms were calculated using the geometric mixing rule Moreover, the energy of the dihedral angle of each of the four atoms in the structure of the alkylthiols is represented by a multiharmonic expression The values of the parameters for the constituent atoms of sphalerite have been reported in our previous study . The bond and nonbond parameters required for the description of the collector molecules are taken from ref (unless stated otherwise) and are summarized in Table . Here, the united-atom model ,,, was applied, in which the electrostatic interactions of the collector molecules are totally ignored, and they interact with other particles only through the Lennard-Jones potential.…”

Section: Methodsmentioning

confidence: 99%

“…The bond and nonbond parameters required for the description of the collector molecules are taken from ref (unless stated otherwise) and are summarized in Table . Here, the united-atom model ,,, was applied, in which the electrostatic interactions of the collector molecules are totally ignored, and they interact with other particles only through the Lennard-Jones potential. In this model, methyl and methylene groups are replaced by a neutral pseudo-atom with exactly the same mass, featuring merely the LJ component of the nonbond potential.…”

Section: Methodsmentioning

confidence: 99%

“…Later, Mar and Klein applied an all-atom model to study the structure of a self-assembled monolayer of alkylthiols on gold as a function of temperature. Adopting the united-atom approach, Iakovlev et al investigated the conformation and packing of normal alkanes and alkylthiols , on liquid mercury at different surface coverages. Such studies are not limited to pure metals, but similar investigations have also been conducted on the organic-modified surface of layered minerals, with alkyl ammonium as the amphiphilic molecule. − …”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Study of Hydrophilic Sphalerite (110) Surface as Modified by Normal and Branched Butylthiols

Anvari

Liu

et al. 2018

Langmuir

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Molecular dynamics simulation was used to study the wettability of the hydrophilic sphalerite (110) surface chemically modified by butylthiols made up of normal and branched alkyl tails, referred to as n-butylthiol and i-butylthiol hereafter, at different adsorption site coverages. Butylthiol molecules were grafted onto the adsorption sites of the surface in two different distributions-ordered and random. The results showed that for a given butylthiol at a given site coverage, random surface distribution yielded a slightly larger contact angle. This observation was attributed to the fact that average distances between the first and second nearest neighbors of butylthiol molecules are shorter in the case of random surface distribution, resulting in smaller patches of bare surface exposed to water molecules compared to those of the ordered surface distribution. Regardless of the tail structure, the random surface distribution exhibited hydrophobic character (i.e., contact angle ≥ 90°) at a relatively low site coverage of about 25%. The test area method and the Kirkwood and Buff approach were adopted to estimate surface energies (γ) of the bare sphalerite (110) surface and the collector monolayer, respectively. Using the obtained γ values of these two pure states, the apparent surface energy as a function of surface coverage was determined based on Cassie's law. This allowed us to estimate the corresponding values of solid-liquid apparent interfacial tension (γ). Both γ and γ exhibit a linear inverse dependence on surface coverage with a crossover point at 25% site coverage (about 50% surface coverage), above which γ falls below γ, leading to contact angles greater than 90°. The results also revealed that contact angles of the two butylthiols are comparable at site coverages below ∼85%, but above that, they are significantly lower for the branched thiols compared to their normal counterparts. Considering the Lennard-Jones interaction energies between the water cluster and the butylthiols, stronger attractive interactions were present in the case of i-butylthiol due to the presence of two methyl groups in its alkyl chain. This difference was the most intense at site coverages above ∼85%.

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Molecular Dynamics Simulation of Alkylthiol Self-Assembled Monolayers on Liquid Mercury

Cited by 8 publications

References 59 publications

Interfacial Tension Modulation of Liquid Metal via Electrochemical Oxidation

Interfacial Tension Modulation of Liquid Metal via Electrochemical Oxidation

Structures of Peptidic H‐wires at Mercury Surface: Molecular Dynamics Study

Molecular Dynamics Study of Hydrophilic Sphalerite (110) Surface as Modified by Normal and Branched Butylthiols

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