Deep eutectic solvents
(DES) are potentially greener solvents obtained
through the complexation of simple precursors which, among other applications,
have been investigated in recent years for their ability to support
the self-assembly of amphiphilic molecules. It is crucial to understand
the factors which influence surfactant solubility and self-assembly
with respect to the interaction of the surfactant molecule with the
DES components. In this work, small-angle neutron scattering (SANS)
has been used to investigate the micellization of cationic (C
n
TAB) and anionic (SDS) surfactants in a ternary
DES comprising choline chloride, urea, and glycerol, where the hydrogen
bond donors are mixed in varying molar ratios. The results show that
in each case either globular or rodlike micelles are formed with the
degree of elongation being directly dependent on the composition of
the DES. It is hypothesized that this composition dependence arises
largely from the poor solubility of the counterions in the DES, especially
at low glycerol content, leading to a tighter binding of the counterion
to the micelle surface and giving rise to micelles with a high aspect
ratio. This potential for accurate control over micelle morphology
presents unique opportunities for rheology control or to develop templated
syntheses of porous materials in DES, utilizing the solvent composition
to tailor micelle shape and size, and hence the pore structure of
the resulting material.
Understanding and manipulating micelle morphology are key to exploiting surfactants in various applications. Recent studies have shown surfactant self-assembly in a variety of Deep Eutectic Solvents (DESs) where both the nature of surfactants and the interaction of the surfactant molecule with the solvent components influence the size, shape, and morphology of the micelles formed. So far, micelle formation has only been reported in type III DESs, consisting solely of organic species. In this work, we have explored the self-assembly of cationic surfactant dodecyl trimethylammonium nitrate/bromide (C12TANO3/C12TAB), anionic surfactant sodium dodecyl sulfate (SDS), and non-ionic surfactants hexaethylene glycol monododecyl ether (C12EO6) and octaethylene glycol monohexadecyl ether (C16EO8) in a type IV DES comprising metal salt, cerium (III) nitrate hexahydrate, and a hydrogen bond donor, urea, in the molar ratio 1:3.5. C12TANO3, C12TAB, C12EO6, and C16EO8 form spherical micelles in the DES with the micelle size dependent on both the surfactant alkyl chain length and the head group, whereas SDS forms cylindrical micelles. We hypothesize that the difference in the micelle shape can be explained by counterion stabilization of the SDS headgroup by polycations in the DES compared to the nitrate/bromide anion interaction in the case of cationic surfactants or molecular interaction of the urea and the salting out effect of (CeNO3)3 in the DES on the alkyl chains/polyethoxy headgroup for non-ionic surfactants. These studies deepen our understanding of amphiphile self-assembly in this novel, ionic, and hydrogen-bonding solvent, raising the opportunity to use these structures as liquid crystalline templates to generate porosity in metal oxides (ceria) that can be synthesized using these DESs.
In this work we present a novel, low temperature and green method for atom-efficient solvothermal synthesis of crystalline, micelle templated cerium IV oxide (ceria) from a Type IV Deep Eutectic...
This work presents a mechanistic understanding of the
synthesis
of small (<3 nm) gold nanoparticles in a nontoxic, eco-friendly,
and biodegradable eutectic mixture of choline chloride and urea (reline)
without the addition of external reducing or stabilization agents.
Reline acts as a reducing agent by releasing ammonia (via urea hydrolysis), forming gold nanoparticles even at trace ammonia
concentration levels. Reline also affects the speciation of the gold
precursor forming gold chloro-complexes, stabilizing Au+ species, leading to an easier reduction and avoiding the otherwise
fast disproportionation reaction. Such a capability is however lost
in the presence of large amounts of water, where water replaces the
chloride ligands in the precursor speciation. In addition, reline
acts as a weak stabilizing agent, leading to small particles (<3
nm) and narrow distributions although agglomerates quickly form. Such
properties are maintained in the presence of water, indicating that
it is linked to the urea stabilization rather than the hydrogen-bonding
network. This work has important implications in the field of green
synthesis of nanoparticles with small sizes, especially for biomedical
and health care applications, due to the nontoxic nature of the components
of deep eutectic solvents in contrast to the conventional routes.
We present planar substrates suitable for investigating the sucrose/triglyceride fat interfaces found in molten chocolate with surface science techniques. The planar sucrose substrates are produced by spin coating sucrose onto hydrophilic, silicon oxide-capped, silicon substrates from millimolar aqueous solutions of sucrose. We present the characterisation of the sucrose film thicknesses and crystallinity using X-ray reflectivity and grazing incidence X-ray diffraction, respectively. These sucrose-coated substrates can be used in flow cells for Quartz Crystal Microbalance with Dissipation (QCM-D) and neutron/X-ray reflectivity measurements, through which triglyceride oils containing the surfactants commonly used in chocolate manufacture can be flowed. This provides a well-defined, planar, sucrose/triglyceride interface, which can be used to probe the solid/liquid interfaces that are found in molten chocolate at the molecular level.
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