Near-surface distributions of soil water and water repellency under three effluent irrigation schemes in a blue gum (Eucalyptus globulus) plantation

Water repellent soils are difficult to irrigate and susceptible to preferential flow, which enhances the potential for accelerated leaching to groundwater of hazardous substances. Over 5 Mha of Australian soil is water repellent, while treated municipal sewage is increasingly used for irrigation. Only if a critical water content is exceeded will repellent soils become wettable. To avoid excessive loss of water from the root zone via preferential flow paths, irrigation schemes should therefore aim to keep the soil wet enough to maintain soil wettability. Our objective was to monitor the near-surface water content and water repellency in a blue gum (Eucalyptus globulus) plantation irrigated with treated sewage. The plantation's sandy soil surface was strongly water repellent when dry. For 4 months, three rows of 15 blue gum trees each received no irrigation, three other rows received 50% of the estimated potential water use minus rainfall, and three more rows received 100%. During this period, 162 soil samples were obtained in three sampling rounds, and their water content (% dry mass) and degree of water repellency determined. Both high and low irrigation effectively wetted up the soil and eliminated water repellency after 2 (high) or 4 (low) months. A single-peaked distribution of water contents was observed in the soil samples, but the water repellency distribution was dichotomous, with 44% extremely water-repellent and 36% wettable. This is consistent with a threshold water content at which a soil sample changes from water repellent to wettable, with spatial variability of this threshold creating a much wider transition zone at the field scale. We characterized this transition zone by expressing the fraction of wettable samples as a function of water content, and demonstrated a way to estimate from this the wettable portion of a field from a number of water content measurements. To keep the plantation soil wettable, the water content must be maintained at a level at which a significant downward flux is likely, with the associated enhanced leaching. At water contents with negligible downward flux, the field is water repellent, and leaching through preferential flow paths is likely. Careful management is needed to resolve these conflicting requirements.

Double layer structure of ionic liquids at the Au(111) electrode interface : an atomic force microscopy investigation

The double layer structure of two ionic liquids (ILs), 1-butyl-1- methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py ₁,₄]FAP) and 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([EMIm]FAP) at the polarized Au(111) electrode interface is probed using Atomic Force Microscopy force measurements. The force-separation profiles suggest a multilayered morphology is present at the electrified Au(111)-IL interface, with more near surface layers detected at higher potentials. At the (slightly negative) open circuit potential, multiple ion layers are present, and the innermost layer, in contact with the Au(111) surface, is enriched in the cation due to electrostatic adsorption. Upon applying negative electrode potentials (-1.0 V, -2.0 V), stronger IL near surface structure is detected: both the number of ion layers and the force required to rupture these layers increases. Positive electrode potentials (+1.0 V, +2.0 V) also enhance IL near surface structure, but not as much as negative potentials, because surface-adsorbed anions are less effective at templating structure in subsequent layers than cations. This interfacial structure is not consistent with a double layer in the Stern-Gouy-Chapman sense, as there is no diffuse layer. The structure is consistent with a capicitative double-layer model, with a very small separation distance between the planes of charge.

Surface structure of SnOxNy thin films deposited using a filtered cathodic arc for novel energy storage systems

Tin oxide/nitride (SnOxNy) thin films were synthesised using a filtered cathodic vacuum arc deposition system. These films were deposited at room temperature with increasing amounts of reactive nitrogen gas to alter the nanostructure. To understand the surface structure of the coatings several techniques were used including scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS). Preliminary results have shown that a cathodic arc can be used to deposit smooth films which exhibit a mixed tin oxide/nitride structure.

Addition of low concentrations of an ionic liquid to a base oil reduces friction over multiple length scales: a combined nano- and macrotribology investigation

The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials. Silica surfaces lubricated with mixtures of the IL trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate and hexadecane are probed using atomic force microscopy (AFM) (nanoscale) and ball-on-disc tribometer (macroscale). At both length scales the pure IL is a much more effective lubricant than hexadecane. At the nanoscale, 2.0 mol% IL (and above) in hexadecane lubricates the silica as well as the pure IL due to the formation of a robust IL boundary layer that separates the sliding surfaces. At the macroscale the lubrication is highly load dependent; at low loads all the mixtures lubricate as effectively as the pure IL, whereas at higher loads rather high concentrations are required to provide IL like lubrication. Wear is also pronounced at high loads, for all cases except the pure IL, and a tribofilm is formed. Together, the nano- and macroscales results reveal that the IL is an effective lubricant additive - it reduces friction - in both the boundary regime at the nanoscale and mixed regime at the macroscale.

Combined nano- and macrotribology studies of titania lubrication using the oil-ionic liquid mixtures

The lubrication of titania surfaces using a series of ionic liquid (IL)-hexadecane mixtures has been probed using nanoscale atomic force microscopy (AFM) and macroscale ball-on-disk tribometer measurements. The IL investigated is trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate, which is miscible with hexadecane in all proportions. At both length scales, the pure IL is a much more effective lubricant than pure hexadecane. At low loads, which are comparable to common industrial applications, the pure IL reduces the friction by 80% compared to pure hexadecane; while the IL-hexadecane mixtures lubricate the titania surface as effectively as the pure IL and wear decreases with increasing IL concentration. At high test loads the adsorbed ion boundary layer is displaced leading to surface contact and high friction, and wear is pronounced for all IL concentrations. Nonetheless, the IL performs better than a traditional zinc-dialkyl-dithophosphate (ZDDP) antiwear additive at the same concentration.

Growth and structure of prismatic boron nitride nanorods

Prismatic boron nitride nanorods have been grown on single crystal silicon substrates by mechanical ball-milling followed by annealing at 1300 °C. Growth takes place by rapid surface diffusion of BN molecules, and follows heterogeneous nucleation at catalytic particles of an Fe/Si alloy. Lattice imaging transmission electron microscopy studies reveal a central axial row of rather small truncated pyramidal nanovoids on each nanorod, surrounded by three basal planar BN domains which, with successive deposition of epitaxial layers adapt to the void geometry by crystallographic faceting. The bulk strain in the nanorods is taken up by the presence of what appear to be simple nanostacking faults in the external, near-surface domains which, like the nanovoids are regularly repetitive along the nanorod length. Growth terminates with a clear cuneiform tip for each nanorod. Lateral nanorod dimensions are essentially determined by the size of the catalytic particle, which remains as a foundation essentially responsible for base growth. Growth, structure, and dominating facets are shown to be consistent with a system which seeks lowest bulk and surface energies according to the well-known thermodynamics of the capillarity of solids.

Electrospinning of nanofibres with parallel line surface texture for improvement of nerve cell growth

Nanofibres having a parallel line surface texture were electrospun from cellulose acetate butyrate solutions using a solvent mixture of acetone and N,N'-dimethylacetamide. The formation mechanism of the unusual surface feature was explored and attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. The fast evaporation of a highly volatile solvent, acetone, from the polymer solution was found to play a key role in the formation of surface voids, while the high viscosity of the residual solution after the solvent evaporation ensured the line surface to be maintained after the solidification. Based on this principle, nanofibres having a similar surface texture were also electrospun successfully from other polymers, such as cellulose acetate, polyvinylidene fluoride, poly(methyl methacrylate), polystyrene and poly(vinylidene fluoride-co-hexafluoropropene), either from the same or from different solvent systems. Polarized Fourier transform infrared spectroscopy was used to measure the polymer molecular orientation within nanofibres. Schwann cells were grown on both aligned and randomly oriented nanofibre mats. The parallel line surface texture assisted in the growth of Schwann cells especially at the early stage of cell culture regardless of the fibre orientation. In contrast, the molecular orientation within nanofibres showed little impact on the cell growth.

Applications of scanning electrochemical microscopy (SECM) for local characterization of AZ31 surface during corrosion in a buffered media

Different modes of scanning electrochemical mapping (SECM) such as surface generation/tip collection (SG/TC), amperometry, AC-SECM and potentiometry were employed to characterize the active/passive domains, hydrogen gas (H2) evolution and local pH on a corroding surface of AZ31 in simulated biological fluid (SBF). It was found that the main domains of H2 evolution are associated with lower insulating properties of the surface as well as higher local pH. The near surface pH was found to be highly alkaline indicating that, even in a buffered solution such as SBF, the local pH on a corroding AZ31 surface can be significantly different to the bulk pH. © 2014 Elsevier Ltd.

Supported silver nanoparticle and near-interface solution dynamics in a deep eutectic solvent

Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally friendly and functional solvents that are, in some ways, advantageous to traditional aqueous systems. While these solvents continue to produce remarkable thin films and nanoparticle assemblies, their interactions with metallic surfaces are complex and difficult to manipulate. In this study, the near-surface region (2-600 nm) of a carbon surface is investigated immediately following silver nanoparticle nucleation and growth. This is accomplished, in situ, using a novel grazing transmission small-angle X-ray scattering approach with simultaneous voltammetry and electrochemical impedance spectroscopy. With this physical and electrochemical approach, the time evolution of three distinct surface interaction phenomena is observed: aggregation and coalescence of Ag nanoparticles, multilayer perturbations induced by nonaggregated Ag nanoparticles, and a stepwise transport of dissolved Ag species from the carbon surface. The multilayer perturbations contain charge-separated regions of positively charged choline-ethylene and negatively charged Ag and Cl species. Both aggregation-coalescence and the stepwise decrease in Ag precursor near the surface are observed to be very slow (∼2 h) processes, as both ion and particle transport are significantly impeded in a DES as compared to aqueous electrolytes. Altogether, this study shows how the unique chemistry of the DES changes near the surface and in the presence of nanoparticles that adsorb the constituent species.

Hippocampal deformation mapping in MRI-negative PET-positive temporal lobe epilepsy

Objectives: To compare hippocampal surface structure, using large deformation high dimensional mapping (HDM-LD), in subjects with temporal lobe epilepsy (TLE) with (HS+ve) and without (HS−ve) hippocampal sclerosis.

Methods: The study included 30 HS−ve subjects matched with 30 HS+ve subjects from the previously reported epilepsy patient cohort. To control for normal right–left asymmetries of hippocampal surface structure, subjects were regrouped based on laterality of onset of epileptic seizures and presence of HS. Gender ratio, age, duration of epilepsy and seizure frequency were calculated for each of the four groups. Final HDM-LD surface maps of the right and left TLE groups were compared to define differences in subregional hippocampal involvement within the groups.

Results: There were no significant differences in comparisons of the left TLE (left HS−ve compared with HS+ve) or right TLE (right HS−ve compared with HS+ve) groups with respect to age, duration of epilepsy or seizure severity scores. HDM-LD maps showed accentuated surface changes over the lateral hippocampal surface, in the region of the Sommer sector, in the hippocampi affected by HS. However, HS−ve hippocampi showed maximal surface changes in a different pattern, and did not involve the region of Sommer sector.

Conclusion: We conclude that differences in segmental volume loss between the HS−ve and HS+ve groups are suggestive that the underlying pathophysiology of hippocampal changes in the two groups is different, and not related to chronic seizure duration or severity.

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000 °C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

Ornament colour selection, visual contrast and the shape of colour preference functions in great bowerbirds, Chlamydera nuchalis

A male bowerbird visual signal includes his own plumage, a structure he  constructs out of plant material and coloured objects (ornaments) he places on or near the structure to make up the bower. Plumage and bower together are used to attract females for mating. Ornaments are known to contrast with plumage, bower structure and visual backgrounds in seven Australian bowerbird species (Endler et al. 2005, Evolution, 50, 1795-1818). We estimated the colour preferences in a wild population of great bowerbirds using artificially coloured objects widely spaced in bird colour space. We found that these birds prefer colours that contrast with their own plumage, the bower structure and the visual backgrounds adjacent to the bower, and that they have very strong dislikes for colours that are similar to their own plumage and to the visual backgrounds. The range of disliked colour hues was much narrower than the range of preferred hues, suggesting that the word 'preference' may be misleading. Preferences for colour are inherently multidimensional and should be studied in the context of their function.

Self-assembly and film stability of a micelle of a single-chain quaternary ammonium amphiphile containing azobenzene on mica

The self-assembling behavior of a single-chain quaternary ammonium amphiphile bearing azobenzene (C₁₂AzoC₆N⁺) on freshly cleaved mica sheet has been investigated by atomic force microscopy (AFM) method. Confocal microscopic Raman spectra confirm the adsorption of the self-assembled monolayer structure. Ex-situ AFM reveals that C₁₂AzoC₆N⁺ forms branch-like stripes indicating the fusion and reorganization of the micelles during drying in air as the in-situ AFM has revealed that surfactant forms spherical micelles on the mica surface. The nano-sized surface structure is strongly dependent on the change of molecular structure, which resulted from photo-induced isomerization. The nano-sized stripe is quite stable even being annealed at 90 °C for 4 h.