3 research outputs found
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 CO<sub>2</sub> Capture
Properties of four polymers of intrinsic
microporosity containing
Tröger’s base units were assessed for CO<sub>2</sub> 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, CO<sub>2</sub> 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 CO<sub>2</sub> 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