Maria Panoukidou1, Charlie Ray Wand2, Annalaura Del Regno3, Richard L Anderson4, Paola Carbone5. 1. Department of Chemical Engineering and Analytical Science, University of Manchester, Manchester M13 9PL, United Kingdom. Electronic address: maria.panoukidou@manchester.ac.uk. 2. Department of Chemical Engineering and Analytical Science, University of Manchester, Manchester M13 9PL, United Kingdom. Electronic address: charlie.wand@manchester.ac.uk. 3. STFC Hartree Centre, Scitech Daresbury, Warrington WA4 4AD, United Kingdom. Electronic address: annalaura.del-regno@basf.com. 4. STFC Hartree Centre, Scitech Daresbury, Warrington WA4 4AD, United Kingdom. Electronic address: richard.anderson@stfc.ac.uk. 5. Department of Chemical Engineering and Analytical Science, University of Manchester, Manchester M13 9PL, United Kingdom. Electronic address: paola.carbone@manchester.ac.uk.
Abstract
HYPOTHESIS: Sodium Laurylethoxysulfate (SLES) is a fundamental ingredient in a wide range of surfactant products and the mapping of its various mesophases is pivotal in predicting the liquid viscosity. Here we want to show that the use of properly parameterised coarse-grained molecular models can provide structural information of the surfactant solutions not easily achievable through experimental characterization. EXPERIMENTS: We use a novel set of Dissipative Particle Dynamics parameters specifically developed for surfactant molecules to construct the first phase diagram of pure SLES in sodium chloride/water solutions. FINDINGS: We found that our DPD model is able to reproduce the range of morphologies expected for these types of ionic surfactants and in agreement with recent rheological data and theoretical predictions based on the packing parameter. We calculated the structure factor for various salt concentrations and show that the change from spherical to worm-like micelles can be inferred also looking at the intensity of the peak at intermediate q-values which decreases in intensity as salt concentrations increase. Varying the ethoxyl groups we observe that the additional ethoxyl group increased the micellar radius and affected the micelles' shape polydispersity in the system. Finally, based on the contour length of worm-like micelles observed at intermediate salt concentrations, a closed mathematical formula is proposed capable of predicting the average micellar contour length given the salt and surfactant concentrations.
HYPOTHESIS: Sodium Laurylethoxysulfate (SLES) is a fundamental ingredient in a wide range of surfactant products and the mapping of its various mesophases is pivotal in predicting the liquid viscosity. Here we want to show that the use of properly parameterised coarse-grained molecular models can provide structural information of the surfactant solutions not easily achievable through experimental characterization. EXPERIMENTS: We use a novel set of Dissipative Particle Dynamics parameters specifically developed for surfactant molecules to construct the first phase diagram of pure SLES in sodium chloride/water solutions. FINDINGS: We found that our DPD model is able to reproduce the range of morphologies expected for these types of ionic surfactants and in agreement with recent rheological data and theoretical predictions based on the packing parameter. We calculated the structure factor for various salt concentrations and show that the change from spherical to worm-like micelles can be inferred also looking at the intensity of the peak at intermediate q-values which decreases in intensity as salt concentrations increase. Varying the ethoxyl groups we observe that the additional ethoxyl group increased the micellar radius and affected the micelles' shape polydispersity in the system. Finally, based on the contour length of worm-like micelles observed at intermediate salt concentrations, a closed mathematical formula is proposed capable of predicting the average micellar contour length given the salt and surfactant concentrations.