Critical micelle concentration of SDS through DPD simulations using COSMO-RS–based interaction parameters, the thermal effects

In order to obtain the critical micellar concentration (CMC) for sodium dodecyl sulfate (SDS) in water at 288.15, 293.15, 298.15, 303.15 and 308.15 K, two approaches were employed: the first, consisting of experimental Isothermal Calorimetric Titration (ITC) and the second by using Dissipative Particle Dynamics (DPD) simulations. To determine the experimental CMC the calorimetric signal was treated with the software D/STAIN, obtaining values between 8.24 and 9.22 mM, which are in good agreement with other experimental determinations. Also the SDS micellization enthalpies found agree with previous experimental reports. The pairwise aij DPD interaction parameters, needed to run the simulations, were obtained from quantum chemistry calculations under the application of the COSMO-RS solvation scheme jointly with the Flory-Huggins theory. A series of systems with variable concentration of SDS in water were simulated for each temperature. Then, the analysis of the percentage of aggregation of SDS molecules at each temperature, enable to visualized the theoretical aggregation isotherms. By delimiting an experimental CMC window, the DPD aggregation isotherms were used to identify the concentration where either the monomeric or micellar states domain. Intersection of linear fits, in the monomeric and in the micellar regime produced theoretical CMCs values from 8.1 to 8.9 mM. These results compare favorably with the experimental determinations at each temperature. [Display omitted]