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The crystalline monolayer of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface at 0.44 monolayers coverage has been observed and characterized by synchrotron X-ray diffraction and differential scanning calorimetry. The experimentally determined monolayer structure hasp2 symmetry with lattice parametersa = 17.77 Å,b = 13.69 Å andν = 39.7°. The unit cell contains two molecules, which are oriented in a plane parallel to the surface. It is proposed that the molecules are arranged such that they are able to form a weak C–H ··· N hydrogen bond between pyridine groups. The monolayer melts at 414 K, which is unusually close to the bulk melting point for a sub-monolayer coverage system. This molecule is chiral when adsorbed on the surface, but both isomers appear in the unit cell leading to no overall chirality in the monolayer. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) numerical modelling of fault displacement enables the building of geological models to represent the complex 3D geometry and geological properties of faulted sedimentary basins. Using these models, cross-fault juxtaposition relationships are predicted in 3D space and through time, based on the geometries of strata that are cut by faults. Forward modelling of fault development allows a 3D prediction of fault-zone argillaceous smear using a 3D application of the Shale Gouge Ratio. Numerical models of the Artemis Field, Southern North Sea, UK and the Moab Fault, Utah, USA are used to demonstrate the developed techniques and compare them to traditional one- and two-dimensional solutions. These examples demonstrate that a 3D analysis leads to significant improvements in the prediction of fault seal, the analysis of the interaction of the sealing properties of multiple faults, and the interpretation of fault seal within the context of sedimentary basin geometry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Delaminated (d) Cu/Zn doped composite efficient for photodisinfection of H 2 O. • Surface vacancies not surface area, influences photoefficiency of composite. • Photo-mineralization of multidrug resistant E. coli and resistance genes ≥ 90 %. • Fluoroquinolone resistance genes significantly reduced in water after two treatment steps. • Sulphonamide genes was removed completely from water after first treatment step. Drinking water contaminated with antibiotic resistant bacteria could result in loss of antibiotic effectiveness in humans, increased healthcare cost and ultimately death. New delaminated photocatalytic composite (DPC) has been prepared. DPC doped with Cu/Zn kept multidrug resistant (MDR) E. coli and its sulphonamide resistance genes in contaminated water at log reduction >6 for 36 h in two disinfection steps under visible-light using fixed-bed mode (downward flow). In contrast, fluoroquinolone resistance genes persisted in treated water after the first disinfection step and were significantly reduced after the second disinfection step. Surface oxygen vacancies were mainly responsible for photoactivity of DPC. No bacteria re-growth was observed in treated water stored in light/dark for 7 days. A 95 % photo-mineralisation of MDR E. coli and its genes was achieved via the release of superoxide radical (in dark/light). Shelf-life study of DPC vs non-delaminated photocatalytic composite over 7 months suggests that the former remained far more efficient than the latter. [ABSTRACT FROM AUTHOR]

Bis(2-ethylhexyl) phosphate (BEHP) was exposed to carbon steel surfaces from dry and water-saturated dodecane. The resulting changes to the surfaces were characterised using spectroscopic techniques (energy dispersive X-ray (EDX), X-ray photoelectron (XPS), and far-infrared reflection absorption (RAIRS) spectroscopies) and polarised neutron reflectometry (PNR). Although there was no observable affinity of BEHP to the steel surface in dry solvent, a layer of rough iron (III) phosphate formed in water-saturated dodecane. The phosphate-reacted steel surface showed some resistance to corrosion by seawater, suggesting the formation of a cohesive barrier against corrosive species. The results support the use of BEHP as an anti-corrosion additive and a viable phosphating agent for steel surfaces. [Display omitted] • Bis(2-ethylhexyl) phosphate indifferent to steel/iron surface in dry dodecane • Organic phosphate-steel reaction immediately initiated on addition of water. • Iron (III) phosphate layer forms from reaction and provides corrosion protection. [ABSTRACT FROM AUTHOR]

• Facile preparation of solar-active nanocomposites from Kaolinite and agrowaste. • Surface oxygen vacancies and defects in crystal lattice control photoactivity. • Photodegradation of drug molecules complete in 30 min. • 100%, 80%, and 50% mineralization of Artemether, Ampicillin and Sulfamethoxazole. • Photocatalyst efficient for treatment of abattoir, river and hand-dug well water. New solar-active nanocomposites free from toxic reagents or precious metals were developed. They were prepared from natural kaolinite clay, Na 2 WO 4 , titania, and biomass. The photocatalytic activity of the nanocomposites against two antibiotics [Ampicillin (AMP) and Sulfamethoxazole (SMX)] and an antimalarial drug [Artemether (ART)] under sunlight suggests an unusually fast photodegradation that is >90% complete in 30 min especially with the photocatalytic nanocomposite prepared from Musa paradisiaca peels (plantain peels) @ 500 °C (TZPP 5). The presence of both biomass and TiO 2 is essential for the effective function of the photocatalytic nanocomposites. With TZPP 5 , ca. 80% and ca. 50% mineralisation of AMP and SMX, respectively, was observed after 60 min. The photocatalytic reaction releases inorganic by-products (SO 4 2 - , NO 3 - and NH 4 +) at levels below WHO permissible limits for drinking water. The presence of anions reduces the efficiency of TZPP 5 , indicating that it releases electrons and reactive oxygen species that are also responsible for photodegradation of the drugs. However, changing concentrations of electrolyte (NaCl) do not influence its efficiency, suggesting that adsorption may not precede photocatalysis, contrary to common models. Reuse studies suggest a slight loss in photodegradation efficiency (≈6%) of the nanocomposite for AMP in the first two cycles followed by subsequent stability at 70% for subsequent cycles. This is different for SMX, which maintained ≈58% removal for all cycles after the 1st cycle. With efficient treatment of raw wastewater from an abattoir, a river, and a hand-dug well for drinking water, the photocatalytic nanocomposite shows potential for treating drinking water especially in point-of-use water treatment devices. [ABSTRACT FROM AUTHOR]

• Isooctane degradation is studied under conditions prevalent at engine cylinder wall. • NO 2 initiates oxidation radical chain in impinged gasoline; >70 products identified. • O 2 Alone, in the absence of NO x , does not produce significant liquid fuel degradation. • If only NO 2 is present, the key reactive intermediates are alkylperoxy radicals. • If both NO and NO 2 are present, the reactive intermediates are alkoxy radicals. A hypothetical mechanism of degradation of the fuel droplet leaking out from the injector nozzle in a direct injection combustion engine has been proposed recently. This involves as a key step a radical chain oxidation initiated by NO 2 and branched by nitric oxide, NO, both produced by the combustion. The degradation causes the formation of injector nozzle carbonaceous deposits. The present work gives an experimental validation of some of the assumptions behind this model. An autoclave is used to oxidize isooctane under conditions relevant to the cylinder wall near the nozzle (~150 °C, 10 bar, 5% O 2 , 100 ppm of NO 2 by mole and 500 ppm NO in the gas phase), and the degradation products are monitored via gas chromatography-mass spectrometry (GC–MS). The results show no observable fuel degradation in the absence of NO x. NO appears to be able to initiate a radical chain by producing NO 2. Nitric oxide also alters the radical chain by transforming the alkyl peroxy radicals (ROO ⋅) to more reactive alkoxy radicals (RO ⋅), resulting in a range of different products. In addition, NO tends to terminate the radical chain by neutralizing a fraction of the alkyl peroxy radicals, producing alkyl nitrates as termination products. The existence of a radical chain is supported by demonstrating the antioxidative action of a radical scavenger. The chemical reaction mechanism is investigated, based on the detected products, and the key species involved in the degradation process are identified. [ABSTRACT FROM AUTHOR]

A cavity model of the effect of a solvent on thermodynamic parameters of dimerization of polar species in non-polar liquids has been developed and compared to experimental data. Bulk solution data have been collected for stearic acid in cyclohexane and in toluene to quantify the extent of self-association of the acid in terms of the dimer self-dissociation constant, Kd. Composition and temperature-dependent experimental data have been collected to determine Kd, the enthalpy of dissociation, and temperature-dependent infrared molar absorption coefficients. The interaction of stearic acid with small amounts of water present in non-aqueous solvents is also addressed and quantified with a hetero-dissociation (or dehydration) constant, Kh. Existing data for acetic acid are also considered. The model connects Kd and Kh to the vapor-phase association equilibria. Solute dipole-solvent quadrupole interactions are shown to have a major effect on Kd in quadrupolar liquids, such as toluene, benzene, and CS2. This work provides important background as a prelude to adsorption studies of these additives from non-aqueous solvents to solid surfaces with relevance to commercial fluids, such as oil-based corrosion inhibitors and friction modifiers. Moreover, the presented theory of the solvent effect on Kd is a first step to generalization of standard implicit solvent models in computational chemistry (such as the polarizable continuum model) to media of significant quadrupolar strength. This is expected to be particularly important for polar species dissolved in CO2 relevant for carbon capture and storage where appropriate models do not currently exist., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Removal of organic species from solid surfaces is a crucial process. The use of oppositely charged surfactants provides a potential method for enhanced removal. Neutron reflectometry has been used to investigate the complex behaviour of a pre-adsorbed and tenacious layer of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on a mica surface, during exposure to different organic species in solution. The anionic surfactant sodium dodecylsulfate (SDS) was shown to be able to remove the cationic layer, but only if anionic micelles were present in solution. To facilitate comparison with the behaviour of a non-ionic surfactant, the direct adsorption of pentaethylene glycol monododecyl ether (C 12 E 5 ) to mica was also studied; low surface coverage adsorption was seen at the critical micelle concentration and above. C 12 E 5 was then found not to remove the cationic layer, but did include into the layer to some degree. The presence of cationic surfactant on the mica was however shown to significantly modify the adsorption behaviour of the non-ionic surfactant., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Using a combination of X-ray diffraction and simulation techniques, we are able to identify a crystalline monolayer of 1,3,5-triiodotrifluorobenzene formed on graphite. The monolayer is found to exhibit an incommensurate hexagonal unit cell with a lattice parameter of 9.28(7) Å, exhibiting a trigonal arrangement of iodine atoms not found in the bulk structure. DFT simulations have been performed exhibiting close agreement with the experimental structure. Importantly these simulations can be used to compare the strength of the intermolecular interactions both with and without Van der Waals corrections. Thus it is possible to estimate that halogen bonding consists of approximately half the total interaction energy. This demonstrates that despite the presence of strong directional non-covalent bonding, dispersion interactions account for a very significant proportion of the total energy., Competing Interests: Disclosure statement No potential conflict of interest was reported by the author(s).

Hypothesis: The mechanism for the spontaneous formation of water droplets at oil/solid interfaces immersed in water is currently unclear. We hypothesize that growth and shrinkage of droplets are kinetically controlled by diffusion of water through the oil, driven by differences in chemical potential between the solid substrate and the aqueous reservoir., Experiments: The formation, growth and shrinkage of water droplets at an immersed oil/solid interface are investigated theoretically and experimentally with three silicone oils. The surface is hydrophobic and the droplets formed are truncated spheres with radius, a, less than 10 μm. The expansion and contraction of the droplets can be controlled by adjusting the difference in chemical potential. The growth kinetics are modelled in terms of water migration through the oil layer which predicts a 2 ∝t., Findings: This is the first study of possible mechanisms for the formation of such interfacial droplets. Several possible causes are shown to be unfavourable, negligible, or are eliminated by careful experiments controlling key parameters (such as oil viscosity, substrate chemistry). The rate constant for mass transport is proportional to difference in chemical potential and an estimate shows dissociation of surface groups on the substrate provides a driving chemical potential of the right magnitude., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

A homologous series of halogen bonding monolayers based on terminally iodinated perfluoroalkanes and 4,4'-bipyridine have been observed on a graphitic surface and noninvasively probed using powder X-ray diffraction. An excellent agreement is observed between the X-ray structures and density functional theory calculations with dispersion force corrections. Theoretical analysis of the binding energies of the structures indicate that these halogen bonds are strong (25 kJ mol -1 ), indicating that the layers are highly stable. The monolayer structures are found to be distinct from any plane of the corresponding bulk structures, with limited evidence of partitioning of hydrocarbon and perfluoro tectons. The interchain interactions are found to be slightly stronger than those in related aromatic systems, with important implications for 2D crystal engineering.

The structure of a crystalline monolayer of 1,3,5-triazine has been characterised using X-ray diffraction. The monolayer is found to exhibit a hexagonal unit cell with a lattice parameter of 6.161(5) Å, indicating the formation of C-H … N hydrogen bonds. DFT simulations have been performed exhibiting close agreement with the experimental structure. By comparing the strength of the intermolecular interactions both with and in the absence of Van der Waals corrections, it is possible to estimate an interaction strength for the weak C-H … N hydrogen bonds., Competing Interests: Disclosure statement No potential conflict of interest was reported by the authors.

The self-assembly and adsorption of the surfactants cetyltrimethylammonium bromide (CTAB) and didodecyldimethylammonium bromide (DDAB) at the muscovite mica-water interface are studied using molecular-dynamics simulations. Adsorption takes place by an ion-exchange mechanism, in which K+ ions are replaced by the organic alkylammonium cations from the solution. Simulations are performed with and without the surface K+ ions, with pure water, and with the surfactants in aqueous solution. CTAB and DDAB form micellar structures in bulk solution, and in the absence of the surface K+ ions, they quickly adsorb and form bilayer structures. The bilayer ordering of CTAB is not perfect, and there is a competition with the formation of cylindrical micelles. DDAB, on the other hand, forms a well-ordered bilayer structure, with the innermost layer showing strong orientational ordering, and the outermost layer being more disordered. The simulations with pure water highlight the molecular ordering and strong electrostatic interactions with the mica-surface atoms. Using simulated scattering length density profiles, the results are compared directly and critically with existing neutron reflectivity measurements. The simulation results are generally consistent with experiments, and yield new insights on the molecular-scale ordering at the mica-water interface.

The adsorption of 4- n -nonylphenol (4NP), carvacrol, and ethanol onto the surface of iron oxide from nonaqueous solutions is presented. It is found that adsorption of 4NP from alkanes is strong and proceeds to monolayer formation, where the molecules are essentially "upright". However, at high relative concentrations, ethanol successfully out-competes 4NP for the iron oxide surface. Estimates of the enthalpy and entropy of binding of 4NP were found to be exothermic and entropically disfavored. Sum frequency generation vibrational spectroscopy data indicate some evidence of binding through a phenolate anion, despite the nonpolar, nonaqueous solvent. Carvacrol is also found to adsorb as a monolayer where the molecules are lying "flat". The adsorption of ethanol onto iron oxide from dodecane was investigated through the use of quantitative NMR, which is a convenient analytical technique for measuring adsorption isotherms. It was concluded that ethanol does not form adsorbed monolayers on the surface. Instead, it partitions onto the surface as a surface-enhanced local phase separation related to its poor solubility in alkane solvents.

The bridging effect of a series of common cations between the anionic mica surface and the AOT anion has been studied in a condition of constant ionic strength and surfactant concentration. It was found that sodium ions did not show any bridging effect in this system; however, calcium, magnesium, and potassium all caused adsorption of the organic to the mica surface. The concentrations at which bridging occurred was probed, revealing that only a very low bridging cation concentration was required for binding. The bridged layer stability was also investigated, and the interaction was shown to be a weak one, with the bound layer in equilibrium with the species in the bulk and easily removed. Even maintaining ionic strength and bridging ion concentration was not sufficient to retain the layer when the free organic in solution was removed.

Surfactants, which contain phenol and amine groups, are commonly used in industries to protect metallic surfaces, and their efficiency depends strongly on factors such as pressure and temperature, solvent properties, and the presence of other surfactants in the system. In this work, we present a molecular simulation study of the competitive adsorption between a multifunctional phenol and amine surfactant model and ethanol at the oil/solid interface formed between iso-octane and a model hematite (α-Fe 2 O 3 ) slab. We show that the surfactant strongly adsorbs at the iso-octane/hematite interface in the absence of ethanol at moderate temperatures. As the concentration of ethanol is increased, the ethanol molecules compete effectively for the adsorption sites on the iron oxide surface. This competition drives the surfactant molecules to remain in the bulk solution, while ethanol forms ordered and strongly coordinated layers at the oil/solid interface, despite the well-known complete miscibility of ethanol in iso-octane in bulk under standard conditions. Potential of mean force calculations show that the free energy of adsorption of the surfactant is approximately two times larger than that for a single ethanol molecule, but the simulations also reveal that a single surfactant chain needs to displace up to five ethanol molecules to adsorb onto the surface. The end result is more favorable ethanol adsorption which agrees with the experimental analysis of similar oil/iron oxide systems also reported in this work.

The layering of ionic liquids close to flat, charged interfaces has been identified previously through theoretical and some experimental measurements. Here we present evidence for oscillations in ion density ('layering') in a long chain ionic liquid (1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) near the interface with mica using two complementary approaches. Neutron reflection at the ionic liquid-mica interface is used to detect structure at a single interface, and surface force balance (SFB) measurements carried out with the same ionic liquid reveal oscillatory density in the liquid confined between two mica sheets. Our findings imply the interfacial structure is not induced by confinement alone. Structural forces between two mica surfaces extend to approximately twice the distance of the density oscillations measured at a single interface and have similar period in both cases.

The layer structure of the dichain alkyl ammonium surfactant, didodecyldimethylammonium bromide (DDAB), adsorbed from water on to silica and mica surfaces has been determined using neutron reflection. Although sometimes considered interchangeable surfaces for study, we present evidence of significant differences in the adsorbed layer structure below the critical micelle concentration. A complete DDAB bilayer was assembled at the water/mica interface at concentrations below the critical micelle concentration (CMC). In contrast it is not until the CMC was reached that the complete bilayer structure formed on the oxidised silicon crystal. Removal of the complete bilayer on both surfaces was attempted by both washing and ion exchange yet the adsorbed structure proved tenacious., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The adsorption of the surfactant Aerosol-OT (AOT) at the calcite-water interface has been investigated using batch adsorption isotherms and neutron reflection. The adsorption isotherms showed that NaAOT adsorption followed S-type adsorption behaviour with a maximum surface excess of 2.5 mg m(-2) but the method could not be used for the investigation of Ca(AOT)2 adsorption owing to the changes in the bulk phase behaviour of the solution. The surface excess, determined by neutron reflection at the critical micelle concentration (CMC), was 2.5 mg m(-2) for Ca(AOT)2 and 1.8 mg m(-2) for NaAOT. The time dependence of the NaAOT adsorption suggests a slow conversion from the sodium to the calcium salt of AOT at the calcite-water interface by binding calcium ions released from the slightly soluble calcite. The layer thickness in both cases was 35 Å which indicates adsorption as bilayers or distorted micelles. At higher concentrations of NaAOT (~10× CMC) adsorption of an AOT lamellar phase was evident from Bragg peaks in the specular reflection. To our knowledge, this is the first time that adsorption of a surfactant at the calcite-water interface has been investigated by neutron reflection. The technique provided significant new insight into the adsorption behaviour of AOT which would not have been accessible using traditional techniques., (Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.)

Neutron reflection and adsorption isotherm measurements have been used to study the adsorption behaviour of hexanoic acid onto α-alumina surfaces. Importantly, the pH dependence of the behaviour has been characterised with a pronounced maximum in adsorption identified at a pH of approximately 5, close to the pKa of the acid. The adsorbed layer is identified as a bilayer, which is reasonable given the hydrophilic nature of both side of the layer, and has a thickness of 13 Å, suggesting significant extent of interdigitation. At pH 5, the layer has much lower extent of hydration relative to the higher pH of 7, consistent with the increased total adsorption at pH 5. A number of different mechanisms for the binding of the hexanoic acid to the surface are considered. The experimental data, combined with calculations using equilibrium/binding constants of the surface and ligands, indicates that a ligand exchange reaction may be the most significant mechanism., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The title 1:1 stoichiometric salt, C7H10N(+)·C7H13O2 (-), is formed by proton transfer between hepta-noic acid and benzyl-amine. This combination contrasts to the recently published 2:1 acid-amine adduct of cation, anion and neutral acid molecule from the same components [Wood & Clarke (2013 ▶). Acta Cryst. E69, o346-o347]. There are N-H⋯O hydrogen bonds of moderate strength in the structure [the most important graph-set motifs are R (2) 4(8) and R (4) 4(12)], as well as weak C-H⋯O inter-actions.

The title salt, C7H10N(+)·C7H13O2(-)·C7H14O2, is an unusual 2:1 stoichiometric combination of two carb-oxy-lic acid mol-ecules and one amine. Although there are crystal structures of a number of 1:1 complexes reported in the literature, 2:1 acid amine complexes are rather uncommon. In this case, a proton is transferred between one acid mol-ecule and the amine to give an acid anion and an ammonium cation whilst the other carb-oxy-lic acid remains protonated. The species inter-act strongly via electrostatic forces and hydrogen bonds. In addition we note that the N atom of the ammonium group makes four close contacts to surrounding O atoms. Three of these are hydrogen bonds with neighbouring acid anions while the fourth does not involve a hydrogen atom but is directed towards the carbonyl O atom of the protonated acid. Each of the acid anion O atoms accepts two hydrogen bonds from adjacent N atoms. There is also evidence of short C-H⋯O contacts. There is disorder (occupancy ratio 0.51:0.49) in the alkyl chain of one of the carb-oxy-lic acid mol-ecules.

A binary mixture of (S)-(-)-1-phenyl-ethanamine and hexa-noic acid was allowed to react to form the title salt, C8H12N(+)·C6H11O2(-). This crystal contains a 1:1 stoichiometric mixture of the acid- and amine-derived species and displays a chiral structure with N-H⋯O hydrogen-bonded chains propagating along the c-axis direction.

A binary mixture of benzyl-amine and hexa-noic acid has been reacted to form the title salt, C(7)H(10)N(+)·C(6)H(11)O(2) (-). This crystal has a 1:1 stoichiometry of acid- and amine-derived species which contrasts with other related species which can have a number of other integer ratios of acid and amine components. The diffraction data indicate complete transfer of a proton from the acid to the amine to give the salt, comprising a cation and anion combination, with the formation of three hydrogen bonds around each ammonium group. This contrasts with other related species.

The mixing of molecules adsorbed from solution to different interfaces has both industrial and academic relevance and the mixing behaviour at the interface is a key to understanding for example, that the surface tension of a mixture of two surfactants is lower than either of the two pure materials and many other effects. In this paper, we report, for the first time, the application of Solid State NMR to the study of alkane/alcohol mixtures, in a range of relative size ratio between 0 and 0.35, adsorbed onto graphite at high, multilayer coverage. Moreover, this paper evaluated, for the first time, the utility of the combined used of 1H and 2H NMR for: (i) determining the surface composition and (ii) making a theoretical approach to the sorption isotherm. A variety of preferential adsorption behaviour is reported. Preferential adsorption of the longer molecule (decane vs. heptanol) from a mixture has been observed. However, if both components are of similar length, the alcohol is preferentially adsorbed (heptanol vs. octane and octanol vs. octane). Finally, a linear relation between the relative size ratio and the amount of alcohol at monolayer coverage is observed., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The title compound, C(10)H(24)N(+)·C(8)H(15)O(2) (-), forms a layered structure in which inter-molecular N(+)-H⋯O hydrogen bonds connect anions and cations, forming a two-dimensional network parallel to (010). The n-alkyl chains of the decyl-ammonium cations pack according to an ortho-rhom-bic 'subcell' with approximate dimensions 5.1 × 7.3 Å, and they are significantly distorted from planarity.

In this letter, the phase behavior of a saturated alkylamide, heptanamide (C(7)), adsorbed on the surface of graphite using synchrotron X-ray diffraction is presented. The diffraction patterns indicate that heptanamide undergoes a solid-solid phase transition in the monolayer at 330 K from pgg symmetry at lower temperatures to p2 symmetry at high temperatures. Other alkylamides with similar carbon chain lengths do not show this phase change, making the C(7) homologue unusual.

We report an investigation of the presence of thin water layers on calcium carbonate particles dispersed in cyclohexane using small-angle neutron scattering. We identify an adsorbed water layer and measure the thickness using contrast variation to optimize the sensitivity of the scattering to the water. We also report the variation in thickness of these water layers in the presence of salt solutions with the variation of salt concentration and valency. We conclude that thin water layers can be observed using SANS; however, the layers are thin and correspond to essentially the hydration of the particle surfaces.

The orientational order parameter of dense colloidal dispersions of plate-like particles as a function of volume fraction is measured using neutron diffraction. This non-invasive experimental approach directly provides the full particle orientation distribution from which the order parameters can be calculated. The orientation parameters are shown to be linked to the solids fractions of the cakes and the macroscopic permeability of the samples. However, this study suggests that, although orientation can be relevant for a given system, other factors can have a stronger influence, for example, the degree of dispersion or colloidal stability of the clay and may be the principle factor that controls permeability. In addition, we report enhanced ordering of these materials under the influence of an external cross-flow field.