Predicting Critical Micelle Concentrations with Molecular Dynamics Simulations and COSMOmic

Abstract

Surfactants are amphiphilic molecules which are capable of forming micelles. Therefore, they are used in many applications. The critical micelle concentration (CMC), the surfactant concentration at which micelles start to form, is an important property of these systems. Here, the applicability of COSMOmic (an extension of COSMO‐RS) to predict CMCs is reported for the first time. Molecular dynamics simulations were used as second method to calculate transfer free energies needed for the calculation of CMCs. In particular, CMCs for poly(oxyethylene) monoalkyl ether surfactants are determined.

COSMOplex: self-consistent simulation of self-organizing inhomogeneous systems based on COSMO-RS

“…The prediction of critical micelle concentrations (CMCs) is of special interest in many areas of formulation science. 13 Here we consider the prediction of the CMCs of ten diverse neutral surfactants. For each surfactant a spherical aqueous micelle model was built with AUTOBOX based on the surfactant geometry, and a COSMOplex calculation with a self-consistent electrostatic field was started.…”

“…Molecular dynamics (MD) simulations are widely used and considered as predictive to study micellar and biomembrane systems. [12][13][14][15] On the one hand, they operate mechanistically on an atomistic scale. On the other hand they are computationally demanding and, thus, they have not found extensive use in microemulsion modelling.…”

“…Several combinations of COSMO-RS and the methods mentioned above have been used already towards predictions of inhomogeneous systems: first, critical micelle concentrations or micelle: water partition coefficients in combination with MD and DPD simulations; 13,28,[41][42][43] second, interfacial tensions, with COSMO-RS calculations fitted to experimental data or combined with DPD simulations; 29,30 and third, equivalent alkane carbon numbers (EACN) of microemulsion systems, with a QSPR model using COSMO-RS parameters for non-polar oil/surfactant/water systems. 31,32 One of the limitations of COSMO-RS was its inability to handle inhomogeneous, structured liquid systems directly on a mechanistic basis.…”

“…While the COSMOmic approach has been proven to be efficient and reliable with respect to the prediction of free energies of solutes at infinite dilution in micellar systems, 41 many applications of eminent practical importance could not be handled by the COSMO-RS model so far, such as the direct prediction of the critical micelle concentration (CMC) of new surfactants and surfactant mixtures, 13 or the effects of finite concentration enrichment of solutes in micelles, as well as the predictive simulation of liquid-liquid interfaces and microemulsions. As a COSMOmic calculation ends up with a detailed prediction for the probability distribution of each solute with respect to position, orientation and conformational population, it was tempting since the beginnings of COSMOmic to calculate the distribution of the constituents of a micellar system, i.e.…”

Cosmoplex: Self-consistent Simulation of Self-organizing Inhomogeneous Systems Based on Cosmo-rs

“…While the COSMOmic approach has been proven to be efficient and reliable with respect to the prediction of free energies of solutes in infinite dilution in micellar systems, its dependence on MD simulations for getting the structure of the micelle prevents its application to many questions of eminent practical importance, as the direct prediction of the critical micelle concentration (CMC) of new surfactants and surfactant mixtures 20 , or the effects of finite concentration enrichment of solutes in micelles, as well as from the predictive simulation of liquid-liquid interfaces and micro-emulsions. As a COSMOmic calculation ends up with a detailed prediction for the probability distribution of each solute with respect to position, orientation and conformational population, it was tempting since the beginnings of COSMOmic to calculate the distribution of the constituents of a micellar system, i.e.…”