Monte Carlo Simulations of Thin Hydrocarbon Films: Composition Heterogeneity and Structure at the Solid–Liquid and Liquid–Vapor Interfaces

Abstract

The structural properties of 10 nm thick lubricant films consisting of binary and ternary n-alkane mixtures (8 ≤ n ≤ 12) adsorbed on a structureless metal substrate were studied for several temperatures and compositions using Monte Carlo simulations. Configurational-bias Monte Carlo identity switch moves are essential to sample the spatial distribution in these mixtures. Longer alkanes are found to preferentially adsorb onto the substrate while shorter alkanes are enriched at the liquid-vapor interface. This preferential adsorption is evident even when the two chains differ by only one methylene unit and the longer chain is the minor component. Enhanced composition heterogeneity and orientational ordering and fewer gauche defects are characteristic features of the first layer near the substrate.

Analysis of the second harmonic generation signal from a liquid/air and liquid/liquid interface

“…It is suggested that orienting parallel to the interface permits to increase the number of favorable interactions with the denser liquid region for the parts of any given molecule in the outermost region. 72 This behavior was also reported in other liquid/water interfaces. 73,74 In Fig.…”

Self-diffusion Coefficient and Structure of Binary n-Alkane Mixtures at the Liquid–Vapor Interfaces

“…It is suggested that this kind of orientation permits improved "anchoring" for the segments of the molecules in the denser liquid region. 10 In the region next to the above area, molecules are favorably parallel to the interface, which is indicated by the negative value. This kind of tendency enhances the molecular interaction between the segments of molecules in this region with the dense fluid phase.…”

“…12 In the past decade, several researchers investigated the systems with alkane mixtures and reported that smaller molecules are adsorbed at the liquid− vapor interfaces. 10,13 Wenzel et al 10 reported that there are no significant structural changes in liquid−vapor interface region when the binary liquid mixture has similar length of alkanes (e.g., hexane−octane mixture). Although the diffusion coefficient of alkane mixtures in the bulk liquid phase is measured by a few researchers using MD simulations, 7,14 the diffusion phenomena and structure of alkane mixtures at the liquid− vapor interface is not a well-understood issue.…”

Twenty years of exceptional success: The molecular education and research consortium in undergraduate computational chemistry (MERCURY)

“…Padgett left the consortium, Gao ( Central State ) rejoined, and Kelly Anderson ( Roanoke College , physical), Aimée Tomlinson ( North Georgia College , physical), and Sudeep Bhattacharyay and Jim Phillips ( University of Wisconsin‐Eau Claire , biophysical and physical) joined, bringing the total to 17 MERCURY investigators. We published 79 peer‐reviewed papers, [ 159–237 ] or 1.5 papers/faculty/year, which is three times the rate for physical science faculty at undergraduate institutions. [ 46 ] The Shields group's collaboration with Brooks Pate resulted in a Science paper on the structures and energetics of the gas‐phase water hexamer, [ 160 ] which has been cited over 250 times.…”

“…Currently, their attention is focused on the interactions of multicomponent liquid solutions with solid substrates. [ 201 ] Additional work has focused on mixtures of alkanes with other organic species (alkenes, alcohols, perfluoroalkanes).…”