Controlling 1D Nanostructures and Handedness by Polar Residue Chirality of Amphiphilic Peptides.

Peptide assemblies are promising nanomaterials, with their properties and technological applications being highly hinged on their supramolecular architectures. Here, how changing the chirality of the terminal charged residues of an amphiphilic hexapeptide sequence Ac-I4 K2 -NH2 gives rise to distinct nanostructures and supramolecular handedness is reported. Microscopic imaging and neutron scattering measurements show thin nanofibrils, thick nanofibrils, and wide nanotubes self-assembled from four stereoisomers. Spectroscopic and solid-state nuclear magnetic resonance (NMR) analyses reveal that these isomeric peptides adopt similar anti-parallel ß-sheet secondary structures. Further theoretical calculations demonstrate that the chiral alterations of the two C-terminal lysine residues cause the formation of diverse single ß-strand conformations, and the final self-assembled nanostructures and handedness are determined by the twisting direction and degree of single ß-strands. This work not only lays a useful foundation for the fabrication of diverse peptide nanostructures by manipulating the chirality of specific residues but also provides a framework for predicting the supramolecular structures and handedness of peptide assemblies from single molecule conformations.

Understanding the Liquid Structure in Mixtures of Ionic Liquids with Semiperfluoroalkyl or Alkyl Chains.

By mixing ionic liquids (ILs), it is possible to fine-tune their bulk and interfacial structure. This alters their physical properties and solvation behavior and is a simple way to prepare a collection of ILs whose properties can be tuned to optimize a specific application. In this study, mixtures of perfluorinated and alkylated ILs have been prepared, and links between composition, properties, and nanostructure have been investigated. These different classes of ILs vary substantially in the flexibility and polarizability of their chains. Thus, a range of useful structural and physical property variations are accessible through mixing that will expand the library of IL mixtures available in an area that to this point has received relatively little attention. In the experiments presented herein, the physical properties and bulk structure of mixtures of 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM][Tf2N] and 1-(1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM-F13][Tf2N] have been prepared. The bulk liquid structure was investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS, respectively) experiments in combination with atomistic molecular dynamics simulations and the measurement of density and viscosity. We observed that the addition of [C8MIM-F13][Tf2N] to [C8MIM][Tf2N] causes changes in the nanostructure of the IL mixtures that are dependent on composition so that variation in the characteristic short-range correlations is observed as a function of composition. Thus, while the length scales associated with the apolar regions (polar non-polar peak─PNPP) increase with the proportion of [C8MIM-F13][Tf2N] in the mixtures, perhaps surprisingly given the greater volume of the fluorocarbon chains, the length scale of the charge-ordering peak decreases. Interestingly, consideration of the contact peak shows that its origins are both in the direct anion···cation contact length scale and the nature (and hence volume) of the chains appended to the imidazolium cation.

Self-Sorting in Diastereomeric Mixtures of Functionalized Dipeptides.

Self-sorting in functionalized dipeptide systems can be driven by the chirality of a single amino acid, both at a high pH in the micellar state and at a low pH in the gel state. The structures formed are affected to some degree by the relative concentrations of each component showing the complexity of such an approach. The structures underpinning the gel network are predefined by the micellar structures at a high pH. Here, we describe the systems prepared from two dipeptide-based gelators that differ only by the chirality of one of the amino acids. We provide firm evidence for self-sorting in the micellar and gel phases using small-angle neutron scattering and cryo-transmission electron microscopy (cryo-TEM), showing that complete self-sorting occurs across a range of relative concentrations.

Acidification-Induced Structure Evolution of Lipid Nanoparticles Correlates with Their In Vitro Gene Transfections.

The rational design of lipid nanoparticles (LNPs) for enhanced gene delivery remains challenging because of incomplete knowledge of their formulation-structure relationship that impacts their intracellular behavior and consequent function. Small-angle neutron scattering has been used in this work to investigate the structure of LNPs encapsulating plasmid DNA upon their acidification (from pH 7.4 to 4.0), as would be encountered during endocytosis. The results revealed the acidification-induced structure evolution (AISE) of the LNPs on different dimension scales, involving protonation of the ionizable lipid, volume expansion and redistribution of aqueous and lipid components. A similarity analysis using an LNP's structural feature space showed a strong positive correlation between function (measured by intracellular luciferase expression) and the extent of AISE, which was further enhanced by the fraction of unsaturated helper lipid. Our findings reveal molecular and nanoscale changes occurring during AISE that underpin the LNPs' formulation-nanostructure-function relationship, aiding the rational design of application-directed gene delivery vehicles.

Peptide Self-Assemblies from Unusual α-Sheet Conformations Based on Alternation of d/l Amino Acids.

Peptide self-assembly is a hierarchical process during which secondary structures formed in the initial stages play a critical role in determining the subsequent assembling processes and final structural ordering. Unusual secondary structures hold promise as a source to develop novel supramolecular architectures with unique properties. In this work, we report the design of a new peptide self-assembly strategy based on unusual α-sheet secondary structures. In light of the strong propensity of leucine toward forming helical conformations and its high hydrophobicity, we design two short amphiphilic peptides Ac-LDLLDLK-NH2 and Ac-DLLDLLDK-NH2 with alternating l- and d-form amino acids. Microscopic imaging, neutron scattering, and spectroscopic measurements indicate that the two heterochiral peptides form highly ordered wide nanotubes and helical ribbons with monolayer thickness, in sharp contrast to twisted nanofibrils formed by the homochiral peptide Ac-LLLLK-NH2. Molecular dynamics simulations from monomers to trimers reveal that the two heteropeptides fold into α-sheets instead of ß-sheets, which readily pack into tubular architectures in oligomer simulations. Simulated circular dichroism spectra based on α-sheet oligomers validate the proposed α-sheet secondary structures. These results form an important basis for the rational design of higher-order peptide assemblies with novel properties based on unusual α-sheet secondary structures.

Nanostructuring with Surfactants: The Self-Assembly of a New Poly(thiophene-phenylene) Conjugated Polymer Bearing Azacrown Ether Pendant Groups.

We report the synthesis of a new conjugated polymer bearing crown ether moieties, poly[(N(1-aza-[18]crown-6)carbamido)thiophene-2,5-diyl-alt-1,4-phenylene] (BG2). In water, BG2 forms a dispersion with a slightly cloudy appearance. We have studied the effect of adding surfactants, with different polar head groups, on these polymer-polymer aggregates. Special attention is given to the system with the anionic surfactant, sodium dodecyl sulfate (SDS). The combination of photophysical techniques with electrical conductivity, NMR (1H, 13C, and 27Na), DFT calculations, molecular dynamics simulations, and small-angle neutron scattering (SANS) provides a detailed picture on the behavior of the SDS/BG2 system in aqueous solution and in thin films. NMR, electric conductivity, and DFT results suggest that hydrophilic interactions occur between the polar headgroup of the surfactant (OSO3- Na+) and the aza-[18]-crown-6 moiety. DFT calculations confirmed the capability of BG2 to form stable complexes with the Na+ cations, where the cation can be either inside the azacrown cavity or sandwiched between the cavity and the polymer chain, which seem to determine the position of the surfactant hydrocarbon chain and, therefore, be responsible for the disruption of the BG2 aggregates and subsequent increase in the photoluminescence quantum yields. SANS measurements, made with hydrogenated and deuterated SDS in D2O, clearly show how micron-sized aggregates of BG2 are broken down by SDS and then how BG2 becomes preferentially incorporated within joint colloidal particles of BG2 and SDS with increasing [SDS]/[BG2] molar ratio.

Small-angle neutron scattering from mixtures of long- and short-chain 3-alkyl-1-methyl imidazolium bistriflimides.

The preparation of mixtures of ionic liquids (ILs) represents an attractive strategy to tune their properties, an important aspect of which is to understand how the structure of the bulk varies with composition. In this study, small-angle neutron scattering (SANS) was used to probe mixtures of methylimidazolium-based ionic liquids [Cnmim][Tf2N] with [C2mim][Tf2N]) (n = 4, 6, 8 and 10) and of [Cmmim][Tf2N] with [C12mim][Tf2N] (m = 2, 4, 6 and 8). Mixtures were prepared in both contrasts, which is to say that one component would be fully hydrogenated while the other was fully deuterated, and vice versa. Data were fitted using a range of appropriate models, of which the Teubner-Strey model provided most useful information and the pure materials showed a nascent Polar Non-polar Peak (PNPP) for n = 6, which became more evident as n increased. In the mixtures [Cnmim]x[C2mim]1-x[Tf2N], the PNPP was evident for n = 10 and 8, nascent for n = 6 and absent for n = 4, with percolation showing a very strong dependence on the chain length of the added IL, [Cnmim][Tf2N]. In contrast, while the ability of [C12mim][Tf2N] to form percolated structures was damped when mixed with [Cmmim][Tf2N], as m increased from 2 to 6, this effect was less strong. However, data obtained for mixtures of [C12mim][Tf2N] and [C8mim][Tf2N], both of which percolate as pure materials, did not fit easily in any of the models applied to the previous systems and gave results that depended on the contrast used. Complementary small-angle X-ray scattering (SAXS) data, however, showed the expected evolution and behaviour of the PNPP, COP and CP, revealing that the unexpected observations were due to an adventitious matching out of isotopic contrasts. As well as revealing details of the structures of these IL mixtures, the results also point to complementary strategies for generating bulk percolated structures as a function of cation chain length.

A guide to designing graphene-philic surfactants.

HYPOTHESIS: As compared to common aliphatic surfactants, increasing the number of pendant or incorporated aromatic groups in a surfactant is expected to offer significant enhancement in the affinity for graphene surfaces. The basis for enhanced graphene-philicity of aromatic surfactants is that they can develop appreciable π - π interactions with graphene. Furthermore, charged (anionic) surfactants are expected to confer electrostatic stabilization on surfactant-graphene composites. Hence, it is expected that anionic aromatic surfactants combine these two properties for effective stabilization of graphene dispersions in water. EXPERIMENTAL: The properties of two custom made graphene-compatible surfactants carrying two and three aromatic moieties in the hydrophobic tails, namely DC3Ph2 (sodium 1,4-dioxo-1,4-bis(3-phenylpropoxy)butane-2-sulfonate) and TC3Ph3 (sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3-phenylpropoxy)carbonyl) pentane-2-sulfonate) were compared with other common ionic commercial surfactants. Air-water (a/w) surface tension measurements were used to assess the surfactant adsorption and interfacial packing in the absence and presence of graphene. The surfactant coverage index for graphene (Ф) was calculated using surfactant headgroup areas derived from a/w surface tension data, chain volumes, and molecular fragment volumes from literature. FINDINGS: Increasing the number of aromatic groups and tails per surfactant was shown to increase the ability of surfactants to pack and fill space, as expressed by Ф. Comparison between the values of Ф for surfactants of different chain structure and architecture showed that the affinity for graphene increased with Ф. Hence, there is an implicit link between surfactant-graphene compatibility and the identity, chemical composition and architecture of the surfactant chains.

Profiling Parkinson's disease cognitive phenotypes via resting-state magnetoencephalography.

Aberrant brain oscillations are a hallmark of Parkinson's disease (PD) pathophysiology and may be related to both motor and nonmotor symptoms. Mild cognitive impairment (MCI) affects many people with PD even at the time of diagnosis and conversion risks to PD dementia (PDD) are very high. Unfortunately, pharmacotherapies are not addressing cognitive symptoms in PD. Profiling PD cognitive phenotypes (e.g., MCI, PDD, etc.) may therefore help inform future treatments. Neurophysiological methods, such as magnetoencephalography (MEG), offer the advantage of observing oscillatory patterns, whose regional and temporal profiles may elucidate how cognitive changes relate to neural mechanisms. We conducted a resting-state MEG cross-sectional study of 89 persons with PD stratified into three phenotypic groups: normal cognition, MCI, and PDD, to identify brain regions and frequencies most associated with each cognitive profile. In addition, a neuropsychological battery was administered to assess each domain of cognition. Our data showed higher power in lower frequency bands (delta and theta) observed along with more severe cognitive impairment and associated with memory, language, attention, and global cognition. Of the total 119 brain parcels assessed during source analysis, widespread group differences were found in the beta band, with significant changes mostly occurring between the normal cognition and MCI groups. Moreover, bilateral frontal and left-hemispheric regions were particularly affected in the other frequencies as cognitive decline becomes more pronounced. Our results suggest that MCI and PDD may be qualitatively distinct cognitive phenotypes, and most dramatic changes seem to have happened when the PD brain shows mild cognitive decline.NEW & NOTEWORTHY Can we better stage cognitive decline in patients with Parkinson's disease (PD)? Here, we provide evidence that mild cognitive impairment, rather than being simply a milder form of dementia, may be a qualitatively distinct phase in its development. We suggest that the most dramatic neurophysiological changes may occur during the time the PD brain transitions from normal cognition to MCI, then compensatory changes further occur as the brain "switches" to a dementia state.

Fabrication and application of composite adsorbents made by one-pot electrochemical exfoliation of graphite in surfactant ionic liquid/nanocellulose mixtures.

Previously, surfactant-assisted exfoliated graphene oxide (sEGO) formed with the triple-chain surfactant TC14 (sodium 1,4-bis(neopentyloxy)-3-(neopentylcarbonyl)-1,4-dioxobutane-2-sulfonate) was applied in wastewater treatment. The extent of dye-removal and the adsorption capacity of the sEGO formed with this triple-chain surfactant outperformed those of two other systems, namely, the di-chain version of TC14 (AOT14; sodium 1,2-bis-(2,2-dimethyl-propoxycarbonyl)-ethanesulfonate) and the single-chain surfactant sodium n-dodecylsulfate. In the present study, to further optimise the surfactant chemical structure, the sodium ion of TC14 was substituted with 1-butyl-3-methyl-imidazolium (BMIM) generating surfactant ionic liquids (SAILs; 1-butyl-3-imidazolium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulfonate), hereafter denoted as BMIM-TC14. This SAIL, together with nanofibrillated kenaf cellulose (NFC), was used to electrochemically exfoliate graphite, yielding BMIM-TC14 sEGO/NFC composites. These highly hydrophobic polymer composites were then used for the removal of methylene blue (MB) from aqueous solution. 1H NMR spectroscopy was used to elucidate the structure of the synthesised SAILs. The morphologies of the resulting nanocomposites were investigated using Raman spectroscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. Analysis using small-angle neutron scattering was performed to examine the aggregation behaviour of sEGO and custom-made SAILs. Zeta potential, surface tension, and dynamic light-scattering measurements were used to study the aqueous properties and colloidal stability of the suspension. Amongst the surfactants tested, BMIM-TC14 sEGO/NFC exhibited the highest MB adsorption ability, achieving 99% dye removal under optimum conditions. These results highlight the importance of modifying the hydrophilic moieties of amphiphilic compounds to improve the performance of sEGO/NFC composites as effective adsorbents for wastewater treatment.

Fracto-eutectogels: SDS fractal dendrites via counterion condensation in a deep eutectic solvent.

Glyceline, a deep eutectic solvent comprising glycerol and choline chloride, is a green nonaqueous solvent with potential industrial applications. Molecular mechanisms of surfactant self-assembly in deep eutectic solvents are expected to differ from those in their constituent polar components and are not well understood. Here we report the observation of self-assembled SDS fractal dendrites with dimensions up to ∼mm in glyceline at SDS concentrations as low as cSDS ∼ 0.1 wt%. The prevalence of these dendritic fractal aggregates led to the formation of a gel phase at SDS concentrations above ≥1.9 wt% (the critical gelation concentration cCGC). The gel microscopic structure was visualised using polarised light microscopy (PLM); rheology measurements confirmed the formation of a colloidal gel, where the first normal stress difference was negative and the elastic modulus was dominant. Detailed nano-structural characterisation by small-angle neutron scattering (SANS) further confirmed the presence of fractal aggregates. Such SDS aggregation or gelation has not been observed in water at such low surfactant concentrations, whereas SDS has been reported to form lamellar aggregates in glycerol (a component of glyceline). We attribute the formation of the SDS fractal dendrites to the condensation of counterions (i.e. the choline ions) around the SDS aggregates - a diffusion-controlled process, leading to the aggregate morphology observed. These unprecedented results shed light on the molecular mechanisms of surfactant self-assembly in deep eutectic solvents, important to their application in industrial formulation.

Ionotropic Gelation Fronts in Sodium Carboxymethyl Cellulose for Hydrogel Particle Formation.

Hydrogel microparticles (HMPs) find numerous practical applications, ranging from drug delivery to tissue engineering. Designing HMPs from the molecular to macroscopic scales is required to exploit their full potential as functional materials. Here, we explore the gelation of sodium carboxymethyl cellulose (NaCMC), a model anionic polyelectrolyte, with Fe3+ cations in water. Gelation front kinetics are first established using 1D microfluidic experiments, and effective diffusive coefficients are found to increase with Fe3+ concentration and decrease with NaCMC concentrations. We use Fourier Transform Infrared Spectroscopy (FTIR) to elucidate the Fe3+-NaCMC gelation mechanism and small angle neutron scattering (SANS) to spatio-temporally resolve the solution-to-network structure during front propagation. We find that the polyelectrolyte chain cross-section remains largely unperturbed by gelation and identify three hierarchical structural features at larger length scales. Equipped with the understanding of gelation mechanism and kinetics, using microfluidics, we illustrate the fabrication of range of HMP particles with prescribed morphologies.

Mixed liposomes containing gram-positive bacteria lipids: Lipoteichoic acid (LTA) induced structural changes.

Lipoteichoic acid (LTA), a surface associated polymer amphiphile tethered directly to the Gram-positive bacterial cytoplasmic membrane, is a key structural and functional membrane component. Its composition in the membrane is regulated by bacteria under different physiological conditions. How such LTA compositional variations modulate the membrane structural stability and integrity is poorly understood. Here, we have investigated structural changes in mixed liposomes mimicking the lipid composition of Gram-positive bacteria membranes, in which the concentration of Bacillus Subtilis LTA was varied between 0-15 mol%. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) measurements indicated formation of mixed unilamellar vesicles, presumably stabilized by the negatively charged LTA polyphosphates. The vesicle size increased with the LTA molar concentration up to ∼6.5 mol%, accompanied by a broadened size distribution, and further increasing the LTA concentration led to a decrease in the vesicle size. At 80 °C, SANS analyses showed the formation of larger vesicles with thinner shells. Complementary Cryo-TEM imaging confirmed the vesicle formation and the size increase with LTA addition, as well as the presence of interconnected spherical aggregates of smaller size at higher LTA concentrations. The results are discussed in light of the steric and electrostatic interactions of the bulky LTA molecules with increased chain fluidity at the higher temperature, which affect the molecular packing and interactions, and thus depend on the LTA composition, in the membrane.

Monolayer wall nanotubes self-assembled from short peptide bolaamphiphiles.

In spite of extensive research, it remains a formidable challenge to control the dimension of the nanostructures self-assembled from short designed peptides. In this work, we show that peptide bolaamphiphiles form monolayer wall nanotubes, facilitated by the interplay between the side chain structure and hydrophobicity of the central residues. The peptide KI4K self-assembles into nanotubes with a width of ~ 100 nm, but changes in the molecular structure of amino acid side chains could hugely impact the nanostructures formed. The three variants of KI4K, via the substitution of aromatic amino acids (F, Y, and Dopa) for the I residue closest to the C-terminus, could substantially reduce nanotube diameters, indicating a significant steric hindrance of the benzene rings on the lateral packing of ß-sheets. However, the introduction of hydroxyl groups on the benzene rings alleviates the steric effect, with nanotube diameter increasing in the order of KI3FK, KI3YK, and KI3DopaK, suggesting the formation of side chain H-bonds between ß-sheets in addition to hydrophobic contacts. Because the self-assembly process of KI3DopaK nanotubes is slow, key intermediates and their structural details are well characterized. With increasing incubation time, monolayered twisted ribbons and helical ribbons grow into mature KI3DopaK nanotubes via the pitch closing route.

Design of Surfactant Tails for Effective Surface Tension Reduction and Micellization in Water and/or Supercritical CO2.

The interfacial properties and water-in-CO2 (W/CO2) microemulsion (µE) formation with double- and novel triple-tail surfactants bearing trimethylsilyl (TMS) groups in the tails are investigated. Comparisons of these properties are made with those for analogous hydrocarbon (HC) and fluorocarbon (FC) tail surfactants. Surface tension measurements allowed for critical micelle concentrations (CMC) and surface tensions at the CMC (γCMC) to be determined, resulting in the following trend in surface activity FC > TMS > HC. Addition of a third surfactant tail gave rise to increased surface activity, and very low γCMC values were recorded for the double/triple-tail TMS and HC surfactants. Comparing effective tail group densities (ρlayer) of the respective surfactants allowed for an understanding of how γCMC is affected by both the number of surfactant tails and the chemistry of the tails. These results highlight the important role of tail group chemical structure on ρlayer for double-tail surfactants. For triple-tail surfactants, however, the degree to which ρlayer is affected by tail group architecture is harder to discern due to formation of highly dense layers. Stable W/CO2 µEs were formed by both the double- and the triple-tail TMS surfactants. High-pressure small-angle neutron scattering (HP-SANS) has been used to characterize the nanostructures of W/CO2 µEs formed by the double- and triple-tail surfactants, and at constant pressure and temperature, the aqueous cores of the microemulsions were found to swell with increasing water-to-surfactant ratio (W0). A maximum W0 value of 25 was recorded for the triple-tail TMS surfactant, which is very rare for nonfluorinated surfactants. These data therefore highlight important parameters required to design fluorine-free environmentally responsible surfactants for stabilizing W/CO2 µEs.

Ordered Nanofibers Fabricated from Hierarchical Self-Assembling Processes of Designed α-Helical Peptides.

Peptide self-assembly is fast evolving into a powerful method for the development of bio-inspired nanomaterials with great potential for many applications, but it remains challenging to control the self-assembling processes and nanostrucutres because of the intricate interplay of various non-covalent interactions. A group of 28-residue α-helical peptides is designed including NN, NK, and HH that display distinct hierarchical events. The key of the design lies in the incorporation of two asparagine (Asn) or histidine (His) residues at the a positions of the second and fourth heptads, which allow one sequence to pack into homodimers with sticky ends through specific interhelical Asn-Asn or metal complexation interactions, followed by their longitudinal association into ordered nanofibers. This is in contrast to classical self-assembling helical peptide systems consisting of two complementary peptides. The collaborative roles played by the four main non-covalent interactions, including hydrogen-bonding, hydrophobic interactions, electrostatic interactions, and metal ion coordination, are well demonstrated during the hierarchical self-assembling processes of these peptides. Different nanostructures, for example, long and short nanofibers, thin and thick fibers, uniform metal ion-entrapped nanofibers, and polydisperse globular stacks, can be prepared by harnessing these interactions at different levels of hierarchy.

NUrF-Optimization of in situ UV-vis and fluorescence and autonomous characterization techniques with small-angle neutron scattering instrumentation.

We have designed, built, and validated a (quasi)-simultaneous measurement platform called NUrF, which consists of neutron small-angle scattering, UV-visible, fluorescence, and densitometry techniques. In this contribution, we illustrate the concept and benefits of the NUrF setup combined with high-performance liquid chromatography pumps to automate the preparation and measurement of a mixture series of Brij35 nonionic surfactants with perfluorononanoic acid in the presence of a reporter fluorophore (pyrene).

Water-in-CO2 Microemulsions Stabilized by an Efficient Catanionic Surfactant.

To facilitate potential applications of water-in-supercritical CO2 microemulsions (W/CO2 µEs) efficient and environmentally responsible surfactants are required with low levels of fluorination. As well as being able to stabilize water-CO2 interfaces, these surfactants must also be economical, prevent bioaccumulation and strong adhesion, deactivation of enzymes, and be tolerant to high salt environments. Recently, an ion paired catanionic surfactant with environmentally acceptable fluorinated C6 tails was found to be very effective at stabilizing W/CO2 µEs with high water-to-surfactant molar ratios (W0) up to ∼50 (Sagisaka, M.; et al. Langmuir 2019, 35, 3445-3454). As the cationic and anionic constituent surfactants alone did not stabilize W/CO2 µEs, this was the first demonstration of surfactant synergistic effects in W/CO2 microemulsions. The aim of this new study is to understand the origin of these intriguing effects by detailed investigations of nanostructure in W/CO2 microemulsions using high-pressure small-angle neutron scattering (HP-SANS). These HP-SANS experiments have been used to determine the headgroup interfacial area and volume, aggregation number, and effective packing parameter (EPP). These SANS data suggest the effectiveness of this surfactant originates from increased EPP and decreased hydrophilic/CO2-philic balance, related to a reduced effective headgroup ionicity. This surfactant bears separate C6F13 tails and oppositely charged headgroups, and was found to have a EPP value similar to that of a double C4F9-tail anionic surfactant (4FG(EO)2), which was previously reported to be one of most efficient stabilizers for W/CO2 µEs (maximum W0 = 60-80). Catanionic surfactants based on this new design will be key for generating superefficient W/CO2 µEs with high stability and water solubilization.

Highly branched triple-chain surfactant-mediated electrochemical exfoliation of graphite to obtain graphene oxide: colloidal behaviour and application in water treatment.

The generation of surfactant-assisted exfoliated graphene oxide (sEGO) by electrochemical exfoliation is influenced by the presence of surfactants, and in particular the hydrophobic tail molecular-architecture. Increasing surfactant chain branching may improve the affinity for the graphite surfaces to provide enhanced intersheet separation and stabilisation of exfoliated sheets. The resulting sEGO composites can be readily used to remove of a model pollutant, the dye, methylene blue (MB), from aqueous solutions by providing abundant sites for dye adsorption. This article explores relationships between surfactant structure and the performance of sEGO for MB adsorption. Double-branched and highly branched triple-chain graphene-compatible surfactants were successfully synthesised and characterised by 1H NMR spectroscopy. These surfactants were used to produce sEGO via electrochemical exfoliation of graphite, and the sEGOs generated were further utilised in batch adsorption studies of MB from aqueous solutions. The properties of these synthesised surfactants were compared with those of a common single-chain standard surfactant, sodium dodecyl-sulfate (SDS). The structural morphology of sEGO was assessed using Raman spectroscopy and field emission scanning electron microscopy (FESEM). To reveal the links between the hydrophobic chain structure and the sEGO adsorption capacity, UV-visible spectroscopy, zeta potential, and air-water (a/w) surface tension measurements were conducted. The aggregation behaviour of the surfactants was studied using small-angle neutron scattering (SANS). The highly branched triple-chain surfactant sodium 1,4-bis(neopentyloxy)-3-(neopentylcarbonyl)-1,4-dioxobutane-2-sulfonate (TC14) displayed enhanced exfoliating efficiency compared to those of the single-and double-chain surfactants, leading to ∼83% MB removal. The findings suggest that highly branched triple-chain surfactants are able to offer more adsorption sites, by expanding the sEGO interlayer gap for MB adsorption, compared to standard single-chain surfactants.

The curious case of SDS self-assembly in glycerol: Formation of a lamellar gel.

HYPOTHESIS: Hydrogen-bonding capacities of polar nonaqueous media significantly affect self-assembly behaviours of surfactants in these media. INTRODUCTION: Glycerol, a nonaqueous hydrogen-bonding solvent, is widely used in industrial formulations due to its desirable physical properties. Surfactants are ubiquitous in such applications; however, surfactant self-assembly in glycerol is not well understood. METHODS: The microscopic structure of the gel phase was studied using a series of imaging techniques: polarised light microscopy (PLM), confocal laser scanning microscopy (CLSM), and environmental scanning electron microscopy (ESEM). The rheological properties of the gel were studied using viscometry and oscillation rheology measurements. Further nano-structural characterisation was carried out using small-angle neutron scattering (SANS). RESULTS: We have observed the unexpected formation of a microfibrillar gel in SDS and glycerol mixtures at a critical gelation concentration (CGC) as low as ~2 wt%; such SDS gelation has not been observed in aqueous systems. The microscopic structure of the gel consisted of microfibres some mm in length and with an average diameter of D ~ 0.5 µm. The fibres in the gel phase exhibited shear-induced alignment in the viscometry measurements, and oscillation tests showed that the gel was viscoelastic, with an elastic-dominated behaviour. Fitting to SANS profiles showed lamellar nano-structures in the gel microfibres at room temperature, transforming into cylindrical-micellar solutions above a critical gelation temperature, TCG ~ 45 °C. CONCLUSIONS: These unprecedented observations highlight the markedly different self-assembly behaviours in aqueous and nonaqueous H-bonding solvents, which is not currently well understood. Deciphering such self-assembly behaviour is key to furthering our understanding of self-assembly on a fundamental level.