Molecular Dynamics Simulation and Experimental Approach to the Temperature Dependent Surface and Bulk Properties of Hexanoic Acid

Abstract

For the first time, bulk and surface properties of hexanoic acid was simulated by classical molecular dynamics and compared with corresponding values we measured in the range of T = 298.15–373.15 K at ambient pressure. AMBER and optimized potential for liquid substance all atom (OPLS-AA) force fields plus our calculations for atoms charges enable simulating density, surface tension, and viscosity, as well as the bulk structural and orientational profile of molecules at the hexanoic acid/vapor interface. The simulated densities are in good agreement within 2.9%, and the simulated surface tension within 2% over the whole range of experimental measurement. On the basis of structural studies, the carboxylic headgroups form tight hydrogen bonding, whereas the alkyl chains loosely interact indication of a high electrostatic to van der Waals interaction ratio prevailing the liquid system. The simulated viscosities agree well at high temperatures with experiment, though the agreement is reduced at low temperatures. This can be attributed to describing hexanoic acid system with strong Coulombic interaction, H-bonding, and weak van der Waals interaction all by the same force field. Quite interestingly, the simulated density profile shows an enhancement at the interface characteristic of liquids of high anisotropic molecules and the ionic liquids.

Using coarse-grained molecular dynamics to understand the effect of ionic liquids on the aggregation of Pluronic copolymer solutions

“…The CG model for diluted Pluronic aqueous solutions previously published 19 24 was chosen since was able to reproduce the most relevant thermodynamic properties. On the other hand, the OPLS 37 force field was selected for the Na[Hex] system since exhibited a good agreement with the experimental and computational results shown by Fotouhabadi et al 26 In this case, the Na[Hex] concentration was 0.5 mol dm -3 in aqueous solution to compare with their results. The ILs CG mapping was as follows; the [Ch] + was represented with two CG beads with a low polar P1 and charged no hydrogen bond capability of Q0 bead for the polar and the nitrogen charged center as shown in 19 Chloride Cland sodium ions Na + CG beads are surrounded by six implicit water molecules emulating the first solvation and the CG bead for water includes four water molecules.…”

“…Fortunately, the atomistic models have been extensively used to describe these compounds where various atomistic force fields, based in OPLS, 21 AMBER 22 or GROMOS, 23 are available for choline ([Ch] + ), chloride (Cl -) and hexanoate ([Hex] -). [24][25][26][27] The radial distribution functions and densities of atomistic models were here taken as a reference and used to find a suitable topology for the CG versions as previously reported for other ILs. 28,29 It must be highlighted that modelling relatively small molecules is difficult with MARTINI mainly due to the 4:1 CG mapping (4 heavy atoms per interaction bead).…”

Theoretical description of 2D-cluster formation of nonionic surfactants at the air/water interface

“…At present, computer development along with high-performance algorithms allows the calculation of the systems with more than million particles. However, modeling the surfactant behavior using systems comprised even just a few hundreds of particles gives interesting results about the structure of amphiphilic monolayers [83] and interface [75], solvation peculiarities of the surfactant hydrophilic parts [84], hydrogen bonding [85], critical micelle concentration (CMC), aggregation number, and assessment of the interfacial tension at the interface [86][87][88]. Particularly, the authors of ref.…”