Modeling Alkyl Aromatic Hydrocarbons with Dissipative Particle Dynamics

Abstract

Building on previous work studying alkanes, we develop a dissipative particle dynamics (DPD) model to capture the behavior of the alkyl aromatic hydrocarbon family under ambient conditions of 298 K and 1 atmosphere. Such materials are of significant worldwide industrial importance in applications such as solvents, chemical intermediates, surfactants, lubricating oils, hydraulic fluids, and greases. We model both liquids and waxy solids for molecules up to 36 carbons in size and demonstrate that we can correctly capture both the freezing transition and liquid-phase densities in pure substances and mixtures. We also demonstrate the importance of including specialized bead types into the DPD model (rather than solely relying on generic bead types) to capture specific local geometrical constructs such as the benzene ring found in the benzyl chemical group; this can be thought of as representing subtle real-world many-body effects via customized pairwise non-bonded potentials.

Phase Behavior of Alkyl Ethoxylate Surfactants in a Dissipative Particle Dynamics Model

“…Specifically we have sampled the phase behavior of C 12 E 6 at 65 wt % in boxes with dimensions of 20 × 20 × 67.5 and 40 × 40 × 16.875. Both of these are of the same volume as the original 30 3 boxes. The phase behavior in these boxes presents as a combination of bridged H 1 transitioning to perforated L α , and vice versa.…”

“…In this work we probe the ability of this force field to reproduce the liquid state phase behavior of these surfactants. We additionally include a more rigorous consideration of the bond angles, motivated by our recent work on waxing in alkanes and aromatic hydrocarbons, , and refine the parameters for two key bead–bead interactions. The revised model captures the phase behavior of the selected surfactants to a reasonable extent, while maintaining performance for CMCs and log P values as in the original work.…”

Phase Behaviour of Alkyl Ethoxylate Surfactants in a Dissipative Particle Dynamics Model

“…As in our previous work, 1 we use the self-interaction cut-offs R ii to capture the contribution of the molecular fragments to the overall molar volumes (here and below i denotes bead type, not individual beads). For this, the Durchschlag and Zipper rules were used to assign R 3 ii values for different beads in proportion to their fragment molar volumes, 30 taking the molar volume of water as a reference for which R 3 ii ≡ r 3 c = 1. Then, between dissimilar bead types we use a simple arithmetic 'mixing rule'…”

“…In this work we probe the ability of this force field to reproduce the liquid state phase behaviour of these surfactants. We additionally include a more rigorous consideration of the bond angles, motivated by our recent work on waxing in alkanes and aromatic hydrocarbons, 2,3 and refine the parameters for two key bead-bead interactions. The revised model captures the phase behaviour of the selected surfactants quite well, whilst maintaining performance for CMCs and log P values as in the original work.…”

Detecting Solution Phase Behavior in Particle Simulations

“…Despite the seemingly dramatic simplification of interactions in the DPD approach, the method has been used to very good effect to study and predict the behaviour of a number of classes of soft-matter and condensed phase systems. These include (but are by no means limited to) simple liquids, 28 surfactant micelle and phase behaviour, [29][30][31][32][33][34][35] polymers, 36,37 hydrocarbon wax formation, 38,39 and solubility. 40,41 3 A common technique used to generate the ternary diagram from simulation places a grid of discreetly sample points across the diagram.…”