Insight into structural properties of polyethylene glycol monolaurate in water and alcohols from molecular dynamics studies.

Ianatul Khoiroh,Ming-Jer Lee,Sze Ying Lee,Mohsen Pirdashti

doi:10.1039/c9ra09688d

Abstract

By means of molecular dynamics (MD) simulations, we explored the structural properties of polyethylene glycol monolaurate (PEGML) in water and in various aliphatic alcohols (methanol, ethanol, 2-propanol, 2-butanol, tert-butanol, and 1-pentanol). The PEGML and the alcohols were simulated using the optimized potentials for liquid simulations, all-atom (OPLS-AA) force field and water using the extended simple point charge (SPC/E) model. From the isothermal-isobaric (NPT, constant number of particles, constant pressure, and constant temperature) ensemble, we extracted the densities from the simulations and compared them with those from experimental results in order to confirm the validity of the selected force fields. The densities from MD simulations are in good agreement with the experimental values. To gain more insight into the nature of interactions between the PEGML and the solvent molecules, we analyzed the hydrogen-bonds, the electrostatic (Coulomb) interactions, and the van der Waals (Lennard-Jones) interaction energies extracted from MD simulations. The results were further strengthened by computing the solvation free energy by employing the free energy perturbation (FEP) approach. In this method, the free energy difference was computed by using the Bennet Acceptance Ratio (BAR) method. Moreover, the radial distribution functions were analyzed in order to gain more understanding of the solution behavior at the molecular level.

Highlights

Polyethylene glycols (PEGs) and their derivatives have widespread applications as specialty nonionic surfactants
These thermodynamic properties are obtained from a single molecular dynamics (MD) simulation run at the desired state point, give
MD simulations for the mixtures containing polyethylene glycol monolaurate (PEGML) with water or various alcohols have been carried out in the present work

Summary

Introduction

Polyethylene glycols (PEGs) and their derivatives have widespread applications as specialty nonionic surfactants These compounds are amphilic macromolecules with the general formula H–(CH2–CH2–O)n–OH where n is the average number of repeating oxyethylene groups. Various surfactant homologs can be synthesized either by varying the number of ethylene oxide repeating units or the length of the alkyl chain of the alcohols. The versatility of these PEG-derived surfactants arises from their efficient solubility with water and most organic solvents such as methylene chloride, ethanol, toluene, acetone, and. When PEG-based surfactants are used in practice, they are generally mixed with other solvents to improve their performance Among those additives, alcohols are the most frequently used to form microemulsions or various solubilized systems. Short to medium chain length alcohols have been used in the tertiary oil recovery process to enhance the stability and decrease the viscosity of the micellar system.[19,20,21] As a result, the higher efficiency can be achieved and this contributes to the cost reduction of the overall process

Methods

Results

Conclusion