Micelle Formation in Alkyl Sulfate Surfactants Using Dissipative Particle Dynamics

We use dissipative particle dynamics (DPD) to study micelle formation in alkyl sulfate surfactants, with alkyl chain lengths ranging from 6 to 12 carbon atoms. We extend our recent DPD force field [J. Chem. Phys. 2017, 147, 094503] to include a charged sulfate chemical group and aqueous sodium ions. With this model, we achieve good agreement with the experimentally reported critical micelle concentrations (CMCs) and can match the trend in mean aggregation numbers versus alkyl chain length. We determine the CMC by fitting a charged pseudophase model to the dependence of the free surfactant on the total surfactant concentration above the CMC and compare it with a direct operational definition of the CMC as the point at which half of the surfactant is classed as micellar and half as monomers and submicellar aggregates. We find that the latter provides the best agreement with experimental results. Finally, with the same model, we are able to observe the sphere-to-rod morphological transition for sodium dodecyl sulfate (SDS) micelles and determine that it corresponds to SDS concentrations in the region of 300–500 mM

Polymers of Intrinsic Microporosity Containing Tröger Base for CO₂ Capture

Properties of four polymers of intrinsic microporosity containing Tröger’s base units were assessed for CO₂ capture experimentally and computationally. Structural properties included average pore size, pore size distribution, surface area, and accessible pore volume, whereas thermodynamic properties focused on density, CO₂ sorption isotherms, and enthalpies of adsorption. It was found that the shape of the contortion site plays a more important role than the polymer density when assessing the capacity of the material, and that the presence of a Tröger base unit only slightly affects the amount adsorbed at low pressures, but it does not have any significant influence on the enthalpy of adsorption fingerprint. A comparison of the materials studied with those reported in the literature allowed us to propose a set of guidelines for the design of polymers for CO₂ capture applications

Characterizing the Structure of Organic Molecules of Intrinsic Microporosity by Molecular Simulations and X‑ray Scattering

The design of a new class of materials, called organic molecules of intrinsic microporosity (OMIMs), incorporates awkward, concave shapes to prevent efficient packing of molecules, resulting in microporosity. This work presents predictive molecular simulations and experimental wide-angle X-ray scattering (WAXS) for a series of biphenyl-core OMIMs with varying end-group geometries. Development of the utilized simulation protocol was based on comparison of several simulation methods to WAXS patterns. In addition, examination of the simulated structures has facilitated the assignment of WAXS features to specific intra- and intermolecular distances, making this a useful tool for characterizing the packing behavior of this class of materials. Analysis of the simulations suggested that OMIMs had greater microporosity when the molecules were the most shape-persistent, which required rigid structures and bulky end groups. The simulation protocol presented here allows for predictive, presynthesis screening of OMIMs and similar complex molecules to enhance understanding of their structures and aid in future design efforts