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

Abstract

We present a dissipative particle dynamics (DPD) model capable of capturing the liquid state phase behavior of nonionic surfactants from the alkyl ethoxylate (C n E m ) family. The model is based upon our recent work [Anderson et al. J. Chem. Phys. 2017 , 147 , 094503] but adopts tighter control of the molecular structure by setting the bond angles with guidance from molecular dynamics simulations. Changes to the geometry of the surfactants were shown to have little effect on the predicted micelle properties of sampled surfactants, or the water–octanol partition coefficients of small molecules, when compared to the original work. With these modifications the model is capable of reproducing the binary water–surfactant phase behavior of nine surfactants (C 8 E 4 , C 8 E 5 , C 8 E 6 , C 10 E 4 , C 10 E 6 , C 10 E 8 , C 12 E 6 , C 12 E 8 , and C 12 E 12 ) with a good degree of accuracy.

Simulating micelle self-assembly to assess potential for viscosity build in surfactant formulations

“…Hereafter we shall, for the most part, express elapsed times in DPD time-units. One DPD time-unit corresponds to ≈ 50 ps of real elapsed time, according to previously reported mappings based on matching diffusion coefficients (Fraaije et al, 2018;Anderson et al, 2023). Hence the adopted DPD time-step of 0.01 DPD time-units corresponds to ≈ 0.5 ps.…”

“…• The first is computational efficiency. We have demonstrated in our previous work (Anderson et al, 2023) that equilibration of micelle structures can take a very large simulation time (at least 10-40 million time-steps in the case presented in the cited literature). Whilst it is technically feasible to simulate such long time-scales given enough resources, to be of practical use it is of our view that the computational screening protocols ought to be more cost efficient and less time consuming than the alternative of running the laboratory trials.…”

“…These latter beads are all the same in the model apart from the charge, in other words free ions in this approach are represented by charged water beads. In developing this model we follow the approach outlined in prior works (Anderson et al, 2017;Anderson et al, 2018;Anderson et al, 2023;Panoukidou et al, 2019;Del Regno et al, 2021;Bray et al, 2020;Bray et al, 2022;Wand et al, 2020), where the bead volumes are based on partial molar volumes (Durchschlag and Zipper, 1994) and the interactions between DPD beads upon log P and density measurements. As this method is now well established we do not give more extensive details here, rather we point to the Supplementary Material.…”

“…Wand et al (2020) calculated how the composition of a mixed surfactant system influences its self-assembly into WLMs. Several other DPD studies have reported on the simulated properties of micelles (Vishnyakov et al, 2013;Lee et al, 2013;Mao et al, 2015;Johnston et al, 2016;Lee et al, 2016;Anderson et al, 2017;Anderson et al, 2018;Anderson et al, 2023;Sangwai and Sureshkumar, 2011;Velinova et al, 2011;Nivón-Ramírez et al, 2022).…”

Simulating micelle self-assembly to assess potential for viscosity build in surfactant formulations

“…Several other DPD studies have reported on the simulated properties of micelles. 20,21,37,[52][53][54][55][56][57][58][59] An important property in the development of surfactant-based formulated products is rheology, which influences a range of behaviors, from the ability of a product to flow from a bottle, the cleaning ability, to sensory interactions. The rheology of a formulation is strongly influenced by the nature of the self-assembled micellar structures present in it, in particular the presence of WLMs.…”