Molecular models for Sodium Dodecyl Sulphate in aqueous solution to reduce the micelle time formation in molecular simulation

Micelle Dynamic Reconstruction to Effectively Modulate the Transmission of Smart Windows

Micelles are extremely dynamic equilibrium aggregates. The size and shape of micelles are subject to appreciable structural fluctuations with the introduction of foreign ions, temperature, etc. The highly dynamic character has for a long time hugely attracted the interest of researchers to investigate the mechanism of micellar structure change and the dependence of their optical properties on the structure change. Herein, taking the most common sodium dodecyl sulfate (SDS) as an example, the aggregation behavior of SDS with excess K⁺ and the effect of temperature on the K⁺/SDS mixed system were detailed and systematically investigated by combining with molecular dynamics simulations and experiments. The addition of K⁺ leads to a reconfiguration of the original micelle structure, resulting in a significant change in micelle size from the nanoscale up to the microscale. And simultaneously, temperature can induce a dynamic process of conjugation/deconjugation of K⁺/SDS micelles in the mixed solution, which is manifested macroscopically by the change of transmittance. Finally, a temperature-responsive smart gel was prepared by introducing K⁺/SDS into a polyacrylamide (PAM) gel, which showed an excellent tunable performance in transmittance (ΔT_550 nm = 60.1%, ΔT_808 nm = 42.72%). The designed smart window shows potential applications in room temperature control (Δt = 4.1 °C) and excellent stability over the course of 50 cycles.

Model for the Simulation of the CnEm Nonionic Surfactant Family Derived from Recent Experimental Results

Using a comprehensive set of recently published experimental results for training and validation, we have developed computational models appropriate for simulations of aqueous solutions of poly(ethylene oxide) alkyl ethers, an important class of micelle-forming nonionic surfactants, usually denoted C_nE_m. These models are suitable for use in simulations that employ a moderate amount of coarse graining and especially for dissipative particle dynamics (DPD), which we adopt in this work. The experimental data used for training and validation were reported earlier and produced in our laboratory using dynamic light scattering (DLS) measurements performed on 12 members of the C_nE_m compound family yielding micelle size distribution functions and mass-weighted mean aggregation numbers at each of several surfactant concentrations. The range of compounds and quality of the experimental results were designed to support the development of computational models. An essential feature of this work is that all simulation results were analyzed in a way that is consistent with the experimental data. Proper account is taken of the fact that a broad distribution of micelle sizes exists, so mass-weighted averages (rather than number-weighted averages) over this distribution are required for the proper comparison of simulation and experimental results. The resulting DPD force field reproduces several important trends seen in the experimental critical micelle concentrations and mass-averaged mean aggregation numbers with respect to surfactant characteristics and concentration. We feel it can be used to investigate a number of open questions regarding micelle sizes and shapes and their dependence on surfactant concentration for this important class of nonionic surfactants.