Molecular dynamics simulations with enhanced sampling methods (metadynamics) are used to probe the mechanism of vinyl polymer-assisted carbon nanotube (CNT) dispersion in N-methyl-2-pyrrolidone (NMP). The polymer dispersants studied are polyvinylpyrrolidone (PVP), hydrogenated nitrile butadiene rubber (HNBR), and polystyrene (PS). It is determined how variations in the nature of the polymer side groups affect their mode of adsorption onto the CNT surface and, consequently, their effectiveness in dispersing CNTs. This correlation is established by comparing the free energy as a function of the distance between two parallel CNTs with and without added polymer. It is found that the adsorption of the pyrrolidone rings in PVP onto the CNT surface and the partial adsorption of the small polar nitrile groups in HNBR each result in disordered polymer layers that penetrate far into the solvent, and the interactions of the dangling polymer parts ensure that these extended protrusions translate to improved steric stabilization as compared to PS. This study not only presents a comprehensive methodology for assessing the effectiveness of polymer-assisted CNT dispersion but also establishes universal design principles for polymers with optimized performance.

Friction and wear reduction by pure and technical grade glycerol monooleates (GMOs) was investigated in commercial and model base oils, including the influence of water and acetic acid (AA) impurities. Small-angle Xray scattering (SAXS) indicated they cause micelle swelling and elongation. AA reduces the separation of OFM from oil at room temperature (RT). Tribotests in a mini-traction machine with white light interferometry (WLI) show that OFMs decrease the traction coefficient, especially at higher temperatures. AA addition also lowered the traction coefficient at RT. X-ray photoelectron spectroscopy (XPS) revealed surface chemical changes that depend on both tribotest conditions and lubricant composition. Wear was associated with the oxidation of metallic iron. The effects of impurities intrinsic to technical GMO appeared to be significant.

Mussel-inspired catechol-containing polymers have a diverse range of potential applications arising from the intra- and inter-molecular interactions enabled by the catechol (CAT) group (i.e. 1,2-dihydroxybenzene). How such interactions underpin self-assembly of catechol-functionalized polymers in non-polar media is of fundamental interest and also critical to their applications but is poorly understood. Here, we have studied the self-assembled nanostructures of four novel catechol-containing polymers in n-dodecane, a model non-polar solvent, using small-angle neutron scattering (SANS). The polymers represented four different architectures - two diblock and two random copolymers, all consisting of a poly(acrylate) backbone with two side chains (a predominant non-polar ethylhexylacrylate (EHA) moiety and a polar catechol-containing moiety (2, 4, or 6 wt% CAT)) in different connectivity. These were also compared with a control homopolymer containing only EHA sidechains. SANS measurements at polymer concentration of 1 wt% in the temperature range T = 20-70 °C showed that the polymer architecture had a significant impact on the morphology of the self-assembled nano-aggregates. These results represent the first experimental observations of self-assembly behaviour of catechol-containing polymers in a non-polar solvent.

Asphaltenes are polycyclic aromatic molecules found in high-molecular-weight fractions of crude oil. They dissolve in aromatic solvents like toluene but not in aliphatic solvents like heptane. Low solubility leads to aggregate formation and many problems in transport applications. Natural asphaltene fractions contain complex mixtures of molecules that vary widely between sources of crude oil, and so the chemical and structural properties are difficult to characterize. Herein, three synthetic asphaltenes containing different oxidation states of sulfur in binary mixtures of toluene and heptane are studied. Aggregate formation is investigated using a combination of small-angle neutron scattering (SANS) and molecular dynamics (MD) simulations. The extent of aggregation is found to depend strongly on both the composition of the solvent and the functionality of the sulfur atom. A benzothiophene-functionalized asphaltene, without any oxygen, forms nanoaggregates in toluene that do not change significantly on addition of heptane. In contrast, asphaltenes containing the sulfoxide or sulfone analogs form nanoaggregates in toluene and much larger clusters above 40% by volume heptane content, with the initial nanoaggregates of the sulfone being slightly larger. Such behavior is apparent in both measured and simulated scattering profiles, and while these techniques probe different length scales, the results are consistent. The microscopic structures of the simulated aggregates are detailed. In systems with low heptane content, the asphaltenes form small clusters of 2-4 molecules, depending on the functionality. In systems with greater heptane content, the sulfoxide and sulfone form larger clusters. The variations in clustering behavior between functional groups and solvents are attributed mainly to the electrostatic interactions between the polar sulfur-containing functional groups, which stabilize "head-to-tail" configurations in the sulfoxide aggregates and more complex branched structures in the sulfone aggregates.

Time-resolved structural changes taking place during the reaction of Ca(OH)2 and CO2 forming different CaCO3 polymorphs, in aqueous and non-aqueous environments, were recorded operando using mid-infrared (mid-IR) and X-ray absorption near-edge structure (XANES) spectroscopy. Results show that Ca(OH)2 directly transforms into calcite in a pure water dispersion. In methanolic media with low water content, calcium di-methylcarbonate (Ca(OCOOCH3)2) is formed, which is hydrolysed to amorphous calcium carbonate (ACC) and vaterite in the presence of sufficient water. The addition of toluene shifts the equilibrium composition further from Ca(OH)2 to ACC and the crystalline forms of CaCO3, probably by affecting the activity of the methoxide intermediate. It can facilitate the formation of aragonite. No Ca(OH)2 conversion was detected in pure ethanol, isopropanol and toluene dispersions, except for nanoscale Ca(OH)2 in ethanolic dispersion, which formed calcium di-ethylcarbonate (Ca(OCOOCH2CH3)2). Our findings underline that vaterite formation is driven by the solution and solid state chemistry related to the reaction via alkoxides and carbonic acid esters of the alcohols, rather than the nucleation process in solution. The alcohol in these systems does not just act as a solvent but as a reactant.

The formation of reverse micelles by aerosol-OT [sodium bis(2-ethylhexyl) sulfosuccinate] in hydrocarbon solvents, and in the presence of water, is studied using a combination of atomistic molecular-dynamics simulations and small-angle neutron scattering (SANS). There have been many previous studies of aerosol-OT and its self-assembly in both water and non-aqueous solvents, but this work is focused on a combined experimental and simulation study of reverse-micelle formation. The effects of hydration (with water-to-surfactant molar ratios in the range 0-60) and solvent (cyclohexane and n-dodecane) are investigated. A force field is adapted that results in spontaneous formation of reverse micelles starting from completely randomized configurations. The computed dimensions of the reverse micelles compare very favourably with those determined in SANS experiments, providing validation of the simulation model. The kinetics of reverse-micelle formation are studied with a 50-ns, 1.7-million-atom system which contains, in the steady state, about 50 reverse micelles. The internal structures of reverse micelles are characterized with mass density profiles, and the effects of solvent, and the structural crossover from highly structured water to 'bulk' water in the core, are detailed. The corresponding changes in the molecular reorientation times of sequestered water are also determined. Overall, the combination of experiment and simulation gives a detailed picture of reverse-micelle self-assembly and structure.

Polymeric surfactants are amphiphilic molecules with two or more different types of monomers. If one type of monomer interacts favorably with a liquid, and another type of monomer interacts favorably with another, immiscible liquid, then polymeric surfactants adsorb at the interface between the two liquids and reduce the interfacial tension. The effects of polymer architecture on the structural and thermodynamic properties of the liquid–liquid interface are studied using molecular simulations. The interface is modeled with a non-additive binary Lennard-Jones fluid in the two-phase region of the phase diagram. Block and gradient copolymer surfactants are represented with coarse-grained, bead-spring models, where each component of the polymer favors one or the other liquid. Gradient copolymers have a greater concentration at the interface than do block copolymers because the gradient copolymers adopt conformations partially aligned with the interface. The interfacial tension is determined as a function of the surface excess of polymeric surfactant. Gradient copolymers are more potent surfactants than block copolymers because the gradient copolymers cross the dividing surface multiple times, effectively acting as multiple individual surfactants. For a given surface excess, the interfacial tension decreases monotonically when changing from a block to a gradient architecture. The coarse-grained simulations are complemented by all-atom simulations of acrylic-acid/styrene copolymers at the chloroform-water interface, which have been studied in experiments. The agreement between the simulations (both coarse-grained and atomistic) and experiments is shown to be excellent, and the molecular-scale structures identified in the simulations help explain the variation of surfactancy with copolymer architecture.

A combination of ex situ and in situ characterization techniques was used to determine the mechanism of calcium carbonate (CaCO3) formation from calcium hydroxide (Ca(OH)(2)) dispersions in methanol/water (CH3OH/H2O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO2) Ca(OH)(2) establishes a reaction equilibrium with CH3OH, forming calcium hydroxide methoxide (Ca(OH)(OCH3)) and calcium methoxide (Ca(OCH3)(2)). Combined ex situ mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO2 reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH3)(2)). This strongly suggests that carbonation takes place by reaction with the Ca(OCH3)(2) formed from a Ca(OH)(2) and CH3OH reaction. Time-resolved XRD indicates that in the presence of H2O the Ca(OCOOCH3)(2) ester releases CH3OH and CO2, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH3)(2) in the absence of H2O mainly leads to the reformation of Ca(OCH3)(2), but this is accompanied by a significant parallel reaction that releases dimethylether (CH3OCH3) and CO2. CaCO3 is the final product in both decomposition pathways. For CH3OH/H2O mixtures containing more than 50 mol % H2O, direct formation of calcite from Ca(OH)(2) becomes the dominant pathway, although the formation of some Ca(OCOOCH3)(2) was still evident in the in situ mid-IR spectra of 20 and 40 mol % CH3OH systems. In the presence of <= 20 mol % H2O, hydrolysis of the ester led to the formation of an ACC sol-gel. In both the 90 and 100 mol % CH3OH systems, diffusion-limited ACC -> vaterite -> calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)(2) in a methanolic phase have been systematically and experimentally characterized.

Optimization of boundary lubrication by tuning the confined molecular structures formed by surface-active additives such as surfactants and polymers is of key importance to improving energy efficiency in mechanical processes. Here, using the surface forces apparatus (SFA), we have directly measured the normal and shear forces between surface layers of a functionalised olefin copolymer (FOCP) in n-dodecane, deposited onto mica using the Langmuir-Blodgett (LB) technique. The FOCP has an olefin backbone decorated with a statistical distribution of polar-aromatic groups, with a structure that we term as "centipede". The effect of lateral confinement, characterised by the surface pressure, Pi(dep), at the air-water interface at which the LB films are transferred, was examined. Normal force profiles revealed that the thickness of the LB films increased significantly with Pi(dep), with the film thickness (t > 20 nm) inferring a multi-layered film structure, consistent with the interfacial characterisation results from synchrotron X-ray reflectivity (XRR) measurements. The coefficient of friction, mu, between the LB films spanned two orders of magnitude from superlubricity (mu similar to 0.002) to much higher friction (mu > 0.1) depending nonlinearly on Pi(dep), with the lowest friction observed at the intermediate Pi(dep). Molecular arrangement upon LB compression leads to the multilayer film with a structure akin to an interfacial gel, with transient crosslinking facilitated by the intra- and inter-molecular interactions between the functional groups. We attribute the differences in frictional behaviour to the different prevalence of the FOCP functional groups at the lubricating interface, which depends sensitively on the degree of compression at the air-water interface prior to the LB deposition. The LB films remain intact after repeated compression (up to pressures of 10 MPa) and shear cycles, indicating strong surface anchorage and structural robustness as a load-bearing and shear-mediating boundary layer. These unprecedented results from the friction measurements between LB films of a statistical copolymer in oil point towards new strategies for tailoring macromolecular architecture for mediating efficient energy dissipation in oil-based tribological applications.

The self-assembly and surface adsorption of glycerol monooleate (GMO) in n-dodecane are studied using a combination of experimental and molecular dynamics simulation techniques. The self-assembly of GMO to form reverse micelles, with and without added water, is studied using small-angle neutron scattering and simulations. A large-scale simulation is also used to investigate the self-assembly kinetics. GMO adsorption onto iron oxide is studied using depletion isotherms, neutron reflectometry, and simulations. The adsorbed amounts of GMO, and any added water, are determined experimentally, and the structures of the adsorbed films are investigated using reflectometry. Detailed fitting and analysis of the reflectometry measurements are presented, taking into account various factors such as surface roughness, and the presence of impurities. The reflectometry measurements are complemented by molecular dynamics simulations, and good consistency between both approaches is demonstrated by direct comparison of measured and simulated reflectivity and scattering length density profiles. The results of this analysis are that in dry systems, GMO adsorbs as self-assembled reverse micelles with some molecules adsorbing directly to the surface through the polar head groups, while in wet systems, the GMO is adsorbed onto a thin layer of water. Only at high surface coverage is some water trapped inside a reverse-micelle structure; at lower surface coverages, the GMO molecules associate primarily with the water layer, rather than self-assemble.

Whilst bottlebrush polymers have been studied in aqueous media for their conjectured role in biolubrication, surface forces and friction mediated by bottlebrush polymers in non-polar media have not been previously reported. Here, small-angle neutron scattering (SANS) showed that a diblock bottlebrush copolymer (oligoethyleneglycol acrylate/ethylhexyl acrylate; OEGA/EHA) formed spherical core-shell aggregates in n-dodecane (a model oil) in the polymer concentration range 0.1-2.0 wt%, with a radius of gyration Rg ∼ 7 nm, comprising 40-65 polymer molecules per aggregate. The surface force apparatus (SFA) measurements revealed purely repulsive forces between surfaces bearing inhomogeneous polymer layers of thickness L ∼ 13-23 nm, attributed to adsorption of a mixture of polymer chains and surface-deformed micelles. Despite the surface inhomogeneity, the polymer layers could mediate effective lubrication, demonstrating superlubricity with the friction coefficient as low as µ ∼ 0.003. The analysis of velocity-dependence of friction using the Eyring model shed light on the mechanism of the frictional process. That is, the friction mediation was consistent with the presence of nanoscopic surface aggregates, with possible contributions from a gel-like network formed by the polymer chains on the surface. These unprecedented results, correlating self-assembled polymer micelle structure with the surface forces and friction the polymer layers mediate, highlight the potential of polymers with the diblock bottlebrush architecture widespread in biological living systems, in tailoring desired surface interactions in non-polar media.

The data presented in this article relates to the crystallisation of 8 single n-alkanes, C16H34 - C23H48 in representative diesel solvents dodecane and toluene, as well as a mixture of these 8-alkanes with a composition representative of real diesel fuel in the same solvents. For the single alkane systems, the data was collected over a range of 5 concentrations ranging from 0.09 - 0.311xi, depending upon the system, and 4 concentrations for the 8-alkane mixture, 0.1 - 0.5xi. Raw average crystallisation and dissolution points as a function of cooling rate (q) from a polythermal methodology are presented. Along with the equilibrium crystallisation and dissolution temperatures, van't Hoff fitting parameters, relative critical undercooling (uc) values as a function of q as well as the calculated values of KG and αdet.

Process analytical technologies are widely used to inform process control by identifying relationships between reagents and products. Here, we present a novel process analytical technology system for operando XAS on multiphase multicomponent synthesis processes based on the combination of a conventional lab-scale agitated reactor with a liquid-jet cell. The preparation of sulfonate-stabilized CaCO3 particles from polyphasic Ca(OH)2 dispersions was monitored in real time by Ca K-edge XAS to identify changes in Ca speciation in the bulk solution/dispersion as a function of time and process conditions. Linear combination fitting of the spectra quantitatively resolved composition changes from the initial conversion of Ca(OH)2 to the Ca(R-SO3)2 surfactant to the ultimate formation of nCaCO3·mCa(R- SO3)2 particles. The system provides a novel tool with strong chemical specificity for probing multiphase synthesis processes at a molecular level, providing an avenue to establishing the relationships between critical quality attributes of a process and the quality and performance of the product.

The structures of amphiphilic block and gradient copolymers in solution and adsorbed onto surfaces are surveyed using molecular-dynamics simulations. A bead-spring model is used to identify the general effects of the different architectures: block and gradient copolymers have equal numbers of solvophilic and solvophobic beads, and the gradient copolymer is represented by a linear concentration profile along the chain. Each type of isolated copolymer forms a structure with a globular head of solvophobic beads, and a coil-like tail of solvophilic beads. The radius of gyration of a gradient copolymer is found to be much more sensitive to temperature than that of a block copolymer due to an unravelling mechanism. At finite concentrations, both gradient and block copolymers self-assemble into micelles, with the gradient copolymers again showing a larger temperature dependence. The micelles are characterised using simulated scattering profiles, which compare favourably to existing experimental data. The adsorption of copolymers onto structureless surfaces is modelled with an attractive potential that is selective for the solvophobic beads, and the surface structures are characterised using the average height of the molecules, and the proportion of beads adsorbed. Both types of copolymer form adsorbed films with persistent micelle-like structures, but the gradient copolymers show a stronger dependence on the strength of the surface interactions and the temperature. Coarse-grained, bead-spring models allow a rapid survey and comparison of the block and gradient architectures, and the results set the scene for future work with atomistic simulations. A superficial but favourable comparison is made between the results from the bead-spring models, and atomistic simulations of a butyl prop-2-enoate/prop-2-enoic acid (butyl acrylate/acrylic acid) copolymer in n-dodecane at room temperature.

The data presented in this article relates to the crystallisation of the long chain hydrocarbon eicosane (C20H42), from supersaturated toluene solutions in the absence/presence of a commercially available cold-flow improver additive (IA) at different solution treat rates. Data was collected for treat rates of 0, 0.1, 0.5, 2, 3, 5 and 10 wt% IA with respect to eicosane, with each treat rate studied over four solution concentrations. Data is collected by transmission vs. solution temperature experimental investigations and is analysed through a conventional transmission analysis route (STR) and a reanalysed route that takes into account multiple phase transformation behaviour (RRT). Average crystallisation and dissolution data is provided over a range of solution concentrations and cooling rates used under a polythermal crystallisation methodology for each analysis route. Equilibrium saturation temperature, supersolubility and metastable zone width data is also presented for each treat rate, concentration and analysis route. Laser transmission as a function of solution temperature profiles are displayed for IA crystallising from toluene solutions. This data relates to the research article: Kaskiewicz, P. L., Downie, R., Dowding, P. J., George, N. & Roberts, K. J. Influence of a Polymeric Additive on the Crystallisability and Nucleation Mechanism for the Model Fuel System of Eicosane Crystallising from Supersaturated Toluene Solutions. J. Cryst. Growth 581, (2021) 126,470. https://doi.org/10.1016/j.jcrysgro.2021.126470

The impact of a commercially available cold flow improver additive (IA) on crystallisation within a model fuel system of eicosane in toluene solutions is investigated. Polythermal crystallisation method utilising turbidometric detection is used to assess the influence of IA addition upon eicosane solubility and nucleation inhibition at different solution IA treat rates, ranging from 0.1 to 10 wt%. Whilst IA is found to have negligible effect upon eicosane solubility, its nucleation is found to be disrupted, resulting in a reduction in crystallisation temperatures as a function of higher IA treat rate, with IA and eicosane phase separation also taking place at treat rates of 2 wt % IA and above. A change from an instantaneous to a progressive nucleation mechanism of eicosane in the absence and presence of IA within solution, respectively, is found. This behaviour is rationalised through the proposition that IA is incorporated within developing eicosane prenucleation clusters, hence disrupting their ability to readily grow to a critical size for nucleation. Nucleation kinetic analysis confirms that at given solution undercoolings, higher IA treat rate reduces the rate of nucleation due to an increase in the effective interfacial tension to nucleation, in line with a higher degree of thermodynamic control of the nucleation process, as might be expected for the progressive nucleation behaviour.

The determination of the NMR spin–spin relaxation rate of water in (purely) aqueous particulate dispersions has been shown to be a convenient and facile experimental approach to probing the composition of near particle surface structures. Here, a systematic study has been undertaken of both non-aqueous and mixed aqueous–non-aqueous solvent particulate dispersions to explore the universality of the solvent relaxation technique. As in the aqueous case, a linear relationship between the surface area present and the solvent relaxation rate is observed, confirming the rapid exchange of the solvent molecules between the surface and the bulk and thereby illustrating the viability of the experimental methodology to study such systems. Crucially, the surface enhancement effect was considerably weaker in non-aqueous systems compared with aqueous dispersions and reflects a potential limitation of the wider deployment of this experimental methodology.

A novel neutron and X-ray reflectometry sample environment is presented for the study of surface-active molecules at solid-liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide-dodecane interface at a shear rate of [Formula: see text] [Formula: see text] using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide-dodecane interface at a shear rate of [Formula: see text] [Formula: see text] was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be [Formula: see text] Å under direct shear at [Formula: see text] [Formula: see text] and [Formula: see text] Å when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at [Formula: see text] [Formula: see text].

Compositionally dependent solution structure is found to influence the solubility, crystallisability and nucleation mechanism of eicosane when crystallising from toluene : acetone mixed-solvent solutions.