A Surface Site Interaction Point Method for Dissipative Particle Dynamics Parametrization: Application to Alkyl Ethoxylate Surfactant Self-Assembly

Ennio Lavagnini,Mark J Williamson,Christopher A Hunter,Joanne L Cook,Patrick B Warren

doi:10.1021/acs.jpcb.0c01895

Abstract

Dissipative particle dynamics (DPD) is a coarse-grained approach to the simulation of large supramolecular systems, but one limitation has been that the parameters required to describe the noncovalent interactions between beads are not readily accessible. A first-principles computational method has been developed so that bead interaction parameters can be calculated directly from ab initio gas-phase molecular electrostatic potential surfaces of the molecular fragments that represent the beads. A footprinting algorithm converts the molecular electrostatic potential surfaces into a discrete set of surface site interaction points (SSIPs), and these SSIPs are used in the SSIMPLE (surface site interaction model for the properties of liquids at equilibrium) algorithm to calculate the free energies of transfer of one bead into a solution of any other bead. The bead transfer free energies are then converted into the required DPD interaction parameters for all pairwise combinations of different beads. The reliability of the parameters was demonstrated using DPD simulations of a range of alkyl ethoxylate surfactants. The simulations reproduce the experimentally determined values of the critical micelle concentration and mean aggregation number well for all 22 surfactants studied.

Highlights

The formation of supramolecular structures such as micelles, vesicles, and bilayer membranes is a fundamentally important process in biology and in the industry with many applications in health and personal care products.[1]
The self-assembly of surfactants is a complicated process, and despite the development of simple tools that can be used to predict some aspects of surfactant behavior based on chemical structure (e.g., the critical packing parameter[2] and the hydrophilic lipophilic balance (HLB)3), the development of new surfactant systems still relies on experimental screening
surface site interaction points (SSIPs) were calculated using methoxymethane for EO, ethane for C2, methane for T, and ethanol for OH. To convert these molecular descriptions to bead descriptions, the SSIPs associated with the hydrogen atoms located at the points of covalent connectivity between beads were removed, i.e., the points indicated by dotted lines in to calculate free energies of transfer for all pairwise combinations of beads (Table 1)

Summary

■ INTRODUCTION

The formation of supramolecular structures such as micelles, vesicles, and bilayer membranes is a fundamentally important process in biology and in the industry with many applications in health and personal care products.[1]. In this approach, different beads are used to represent chemical subgroups containing between one and three heavy atoms, as in Anderson et al This provides flexibility and allows straightforward extension to more complicated systems. One approach is to use the same self-interaction parameter for all beads, and the water aii parameter derived from compressibility data is imation commonly used assumes that all (25 beads khBaTv)e.2t7heHsoamweevveor,lutmhies,2a5psporowxeuse self-interaction parameters reported by Anderson et al, which were tuned to match the experimental densities of selected molecular liquids.[37]

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES