Outer Surface Layer Research Articles

Sensing the Ultrastructure of Bacterial Surfaces and Their Molecular Binding Forces Using AFM.

In this protocol, we provide a detailed step-by-step bacterial surface imaging and molecular analysis procedure. With SPM (scanning probe microscopy)-based dynamic force microscopy (DFM) imaging, we achieved a so far unprecedented resolution of ~1nm on the outer surface layer of Tannerella forsythia and monitored the production of curli fibers on Escherichia coli in physiological conditions. Moreover, using these immobilization methods, single-molecule force spectroscopy experiments were conducted on living bacterial cells.

The structural and the photoelectrochemical properties of ZnO-ZnS/ITO 1D hetero-junctions prepared by tandem electrodeposition and surface sulfidation: on the material processing limits.

ZnO–ZnS 1D hetero-nanostructures were prepared by an easy and scalable processing route. It consists of ZnO nanorod electrodeposition on ITO substrate and surface sulfidation by ion exchange in an aqueous Na2S solution. Increasing the treatment contact time (tc) from 8 to 48 h involves different ZnS growth mechanisms leading to different structural and microstructural rod characteristics, even if the overall size does not change significantly. Grazing X-ray diffraction, high-resolution microscopy, energy-dispersive spectrometry and X-ray photoelectron spectroscopy describe the outer surface layer as a poly- and nanocrystalline ZnS blende shell whose thickness and roughness increase with tc. The ZnO wurtzite–ZnS blende interface goes from continuous and dense, at short tc, to discontinuous and porous at long tc, indicating that ZnS formation proceeds in a more complex way than a simple S2−/O2− ion exchange over the treatment time. This feature has significant consequences for the photoelectrochemical performance of these materials when they are used as photoanodes in a typical light-assisted water splitting experiment. A photocurrent (Jp) fluctuation of 45% for less than 5 min of operation is observed for the sample prepared with a long sulfidation time while it does not exceed 15% for that obtained with a short one, underlining the importance of the material processing conditions on the preparation of valuable photoanodes.

Strontium isotope fractionation during strontianite (SrCO3) dissolution, precipitation and at equilibrium

In this study we examine the behavior of stable Sr isotopes between strontianite [SrCO3] and reactive fluid during mineral dissolution, precipitation, and at chemical equilibrium. Experiments were performed in batch reactors at 25°C in 0.01M NaCl solutions wherein the pH was adjusted by bubbling of a water saturated gas phase of pure CO2 or atmospheric air. The equilibrium Sr isotope fractionation between strontianite and fluid after dissolution of the solid under 1atm CO2 atmosphere was estimated as Δ88/86SrSrCO3-fluid = δ88/86Sr SrCO3−δ88/86Srfluid=−0.05±0.01‰. On the other hand, during strontianite precipitation, an enrichment of the fluid phase in 88Sr, the heavy isotopomer, was observed. The evolution of the δ88/86Srfluid during strontianite precipitation can be modeled using a Rayleigh distillation approach and the estimated, kinetically driven, fractionation factor αSrCO3-fluid between solid and fluid is calculated to be 0.99985±0.00003 corresponding to Δ88/86SrSrCO3-fluid = −0.15‰. The obtained results further support that under chemical equilibrium conditions between solid and fluid a continuous exchange of isotopes occurs until the system approaches isotopic equilibrium. This isotopic exchange is not limited to the outer surface layer of the strontianite crystal, but extends to ∼7–8 unit cells below the crystal surface. The behavior of Sr isotopes in this study is in excellent agreement with the concept of dynamic equilibrium and it suggests that the time needed for achievement of chemical equilibrium is generally shorter compared to that for isotopic equilibrium. Thus it is suggested that in natural Sr-bearing carbonates an isotopic change may still occur close to thermodynamic equilibrium, despite no observable change in aqueous elemental concentrations. As such, a secondary and ongoing change of Sr isotope signals in carbonate minerals caused by isotopic re-equilibration with fluids has to be considered in order to use Sr isotopes as environmental proxies in aquatic environments.

32‐3: Stability Enhancement of Light Emitting Diode Based on Quantum Dots through Atomic Layer Deposition

In this work, atomic layer deposition (ALD) technique has been used as an efficient method to improve the operational stability of quantum dots (QDs) optimized white light emitting diode (WLED), by depositing an alumina layer on the outer surface layer. The luminescent microspheres (LMS) were also employed as QDs composite which had been integrated with yellow phosphors on‐chip packed on blue LED to achieve white light with high color rendering.

Surface morphology and passive film composition after pickling and electropolishing

In this work, a novel method of selecting the most favourable electropolishing (EP) conditions is presented as a compromise between the processing time and obtaining the lowest possible roughness value of Sa or Sq (commonly used parameters) as well as the gradual increase of parameters highlighted in this work Ssk and Sku. The results showed that the most appropriate EP charge input should be higher than 1.2 Amin cm−2 and lower than 2.3 Amin cm−2. XPS high-resolution spectra revealed that pickling and EP of the samples results in a decrease of the ratio of the iron oxides amount (at.-%) to the total amount of chromium oxides and hydroxides (at.-%) in the passive film. This ratio gradually decreases reaching the values 1.2, 1.0 and 0.7 for as-received, pickled and electropolished samples, respectively. This result demonstrates iron dissolution of the outer surface layer by pickling and EP.

Structural and magnetic properties of multi-core nanoparticles analysed using a generalised numerical inversion method

The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions.

Elucidating the structural organization of a novel low-density lipoprotein nanoparticle reconstituted with docosahexaenoic acid

Low-density lipoprotein nanoparticles reconstituted with unesterified docosahexaenoic acid (LDL-DHA) is promising nanomedicine with enhanced physicochemical stability and selective anticancer cytotoxic activity. The unique functionality of LDL-DHA ultimately relates to the structure of this nanoparticle. To date, however, little is known about the structural organization of this nanoparticle. In this study chemical, spectroscopic and electron microscopy analyses were undertaken to elucidate the structural and molecular organization of LDL-DHA nanoparticles. Unesterified DHA preferentially incorporates into the outer surface layer of LDL, where in this orientation the anionic carboxyl end of DHA is exposed to the LDL surface and imparts an electronegative charge to the nanoparticles surface. This negative surface charge promotes the monodisperse and homogeneous distribution of LDL-DHA nanoparticles in solution. Further structural analyses with cryo-electron microscopy revealed that the LDL-DHA nanostructure consist of a phospholipid bilayer surrounding an aqueous core, which is distinctly different from the phospholipid monolayer/apolar core organization of plasma LDL. Lastly, apolipoprotein B-100 remains strongly associated with this complex and maintains a discrete size and shape of the LDL-DHA nanoparticles similar to plasma LDL. This preliminary structural assessment of LDL-DHA now affords the opportunity to understand the important structure–function relationships of this novel nanoparticle.

Very low dielectric loss and giant dielectric response with excellent temperature stability of Ga3 + and Ta5 + co-doped rutile-TiO2 ceramics

A newly discovered donor/acceptor co-doped rutile-TiO2 with an extremely high permittivity (ε′) and low loss tangent (tanδ) has stimulated much research in capacitors and high-energy-density storage devices. However, poor high-temperature stability of ε′ prevents its use in practical applications. Here, excellent dielectric properties with a very low tanδ≈0.017–0.079 at 1kHz, high ε′≈5.5×103–3.5×104 and good dielectric-temperature stability with a temperature coefficient, Δε′(T)/ε′RT<±15%, over a wide temperature range (e.g., Δε′(200°C)/ε′RT=6.26%) were simultaneously achieved in heat-treated Ga3+ and Ta5+ co-doped TiO2 (GTTO) ceramics. Both ε′ and tanδ were nearly independent of DC bias up to 40V. Notably, extremely large total-resistivity values of the insulating components were achieved (106–1010Ω·cm) over the temperature range of 20–150°C. These excellent electrical parameters are extremely hard to simultaneously realize in most giant dielectric materials. According to a first-principles study, there is a rather small coupling between 2Ta diamond and 2GaVo triangular shapes. Therefore, improvement of dielectric permittivity comes from insulating layers. Both the insulating grain boundaries and resistive thin outer-surface layers have remarkable influences on the high-performance giant dielectric properties of GTTO ceramics.

Surface barrier layer effect in (In + Nb) co‐doped TiO2 ceramics: An alternative route to design low dielectric loss

AbstractGiant dielectric permittivity (ε′) with low loss tangent (tanδ) was reported in (In + Nb) co‐doped TiO2 ceramics. Either of electron‐pinned defect‐dipole or internal barrier layer capacitor model was proposed to be the origin of this high dielectric performance. Here, we proposed an effectively alternative route for designing low‐tanδ in co‐doped TiO2 ceramics by creating a resistive outer surface layer. A pure rutile‐TiO2 phase with a dense microstructure and homogeneous dispersion of dopants was achieved in (In + Nb) co‐doped TiO2 ceramics prepared by a simple sol‐gel method. Two giant dielectric responses were observed in low‐ and high‐frequency ranges, corresponding to extremely high ε′≈106‐107 and large ε′≈104‐105, respectively. After annealing in air, a low‐frequency dielectric response disappeared and could be restored by removing the outer surface of the annealed sample, indicating the dominant electrode effect in the initial sample. Annealing can cause improved dielectric properties with a temperature‐ and frequency‐independent ε′ value of ≈1.9 × 104 and cause a decrease in tanδ from 0.1 to 0.035. High dielectric performance in (In0.5Nb0.5)xTi1−xO2 ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer.

ASSESSMENT OF CRACKING RESISTANCE OF CELLULAR CONCRETE PRODUCTS UNDER MOISTURE AND CARBONISATION DEFORMATIONS WITH STRESS RELAXATION

Objectives. On the basis of the experimental, theoretical and field studies, an engineering calculation method was developed for assessing the cracking resistance of external enclosing constructions made of cellular concrete, with the maximum gradient development of moisture and carbonisation forced deformations along their thickness, taking into account the relaxation of the shrinkage stresses. In this regard, the aim of the work is to provide technological measures at the manufacturing stage in order to increase the operational cracking resistance of the construction's outer surface layers by reducing the moisture and carbonation shrinkage of cellular concrete by introducing a large or fine porous aggregate in calculated amounts. Methods. A number of analytical equations were applied to establish the dependence of the shrinkage of heavy concrete of conventional hardness on the amount of aggregate introduced and its elasticity modulus, water-cement ratio and cement consumption, as well as the concrete's moisture content. Results. Knowing the volumes of the structural aggregate and the cellular concrete mass, as well as their modulus of elasticity, the shrinkage reduction factor of the cellular concrete was calculated with the addition of a lightweight porous aggregate. Subsequently, the shrinkage deformations of concrete in the surface layer of the outer enclosing construction, maximising crack resistance due to moisture exchange and carbonation influences under operating conditions, were defined, taking into account the relaxation of tensile stresses due to creep of concrete. Conclusion. Theoretical calculations, based on the recommended method of assessing the cracking resistance of cellular concrete enclosing constructions under moisture exchange and carbonisation processes, taking into account the relaxation of shrinkage stresses, showed that in order to exclude the appearance of cracks in wall panels 280 mm thick made of 700 kg/m3 gas ash concrete with elasticity modulus of 2500 MPa, it is necessary to have 70-80% of keramzite or granulated slag, and 50-60% of stone crumb (granite or marble crushed stone) of the volume of cellular concrete in the surface layer of 30-50 mm.

Vibration and instability analysis of fluid-conveying nanotubes embedded in visco-elastic medium with consideration of surface effect

We establish an analytical model to investigate the surface effects on the vibration and instability of fluid-conveying nanotubes embedded in visco-elastic medium. Based on nonlocal elastic theory and Euler-Bernoulli beam theory, the vibration equation of fluid-conveying nanotubes is established with considering three typical boundary conditions. The effects of both inner and outer surface layers on the nanotubes are taken into consideration and the Kelvin-Voigt model is introduced. The results show that the boundary conditions of system, the damping and elastic coefficient of the surrounding medium, thickness of nanotubes and aspect ratios have significant effects on the dynamic behaviors of the nanotubes. The damping parameter of the visco-elastic foundation causes an obvious reduction of the critical flow velocity. For smaller tube thickness, larger aspect ratio or higher elastic parameter of surrounding foundation, the stability of the nanotubes may be greatly enhanced. This article might be helpful for the design and improvement of nanotubes for fluid-conveying applications embedded in elastic medium in nanoelectromechanical systems and microelectromechanical systems.

Effect of titanium doping on the compositional homogeneity of hollow glass microsphere

Titanium doped hollow glass microspheres (HGMs) were fabricated by sol-gel method. There were two kinds of spheres, blue and colorless, in each batch of HGMs. To study the effect of titanium doping on the compositional homogeneity and the difference between the two classes of HGMs, titanium doped gel precursors and HGMs were characterized by XRD, XRF, SIMS, SEM and EDS. The results showed that precipitation of alkali chlorides reduced the uniformity of heavily doped gel precursors and increased the dispersions of doping concentration in batches of HGMs. Because of the movability and flowability at high temperature, the uniformities of alkali metals were relatively poor in all HGMs. The DSIMS depth profiles of HGMs showed that local loss and accumulation of glass network modifiers, especially alkali metals, occurred in the outer and inner surface layers in dozens of nanometers as a result of volatilization and migration in furnace. Titanium behaved as both glass network former and modifier and its uniformity was between that of alkali metals and silicon. In blue HGMs, crystallization and segregation of titanium oxide, furthermore, reduced the compositional homogeneity of blue spheres in comparison to that of the colorless one.

Gas-enhanced operation and stepwise organic stressing as a new alternative in realising successful sludge granulation in high-rate anaerobic bioreactor for wastewater treatment

ABSTRACTAnaerobic biotechnology is becoming the method of choice for many types of wastewater treatment. Application of granular sludge in the upflow anaerobic sludge bed (UASB) is important in maximising the overall treatment capacity benefiting from its fast settling ability and excellent biological activities. This study explores a new alternative for achieving sludge granulation in a sulfidogenic UASB reactor. Granules were first observed at day 30 and achieved the average diameters of 820 µm at day 162. The scanning electron microscope analysis showed that the granules have a regular spherical-shaped outline boundary, and a rough outer surface layer with a channel-like porous structure. The confocal laser scanning microscopy analysis illustrated that the extracellular polymeric substances (EPS) were more evenly distributed across the granules under a gas-enhanced operation than at the control stage. For the control stage operation without gas-enhanced operation, no granule disintegration was observed...

Process control for thermal-spray deposition of thermoset coatings using computer simulation

Thermal spraying is a green solvent-free process with the potential of applying polymer coatings to large components in-house or on-site without the need for prolonged drying. Almost no systematic research has been undertaken on thermally spraying thermoset coatings owing to the complexity and difficulty of managing the curing process. An adequately cured thermoset coating could not be deposited by thermal spraying owing to insufficient cumulative time above the cure temperature. Preheating and post-heating the substrate under a constant heat source were not successful as they led to non-uniform curing, residual stress and the risk of overheating. This study develops and validates a computer model that simulates the deposition of thermoset coatings on metal substrates using thermal spraying and high-energy infrared irradiation. The model uses readily-available commercial software and enables precise control of the coating process to improve energy efficiency and coating quality. Further research showed that evenly cured coatings could be achieved by using variable heat fluxes and controlled utilization of inward conduction from the outer surface layers. Self curing during cooling was significant and maybe employed to increase energy efficiency. The thickness of the metal substrate was shown to be an important variable as it acts as a heat sink and, for heavy sections, can substantially increase energy consumption. The results indicate a need for sufficiently accurate process control and provide a suitable methodology for the deposition of thermoset coatings.

Colossal permittivity in (In1/2Nb1/2)xTi1−xO2 ceramics prepared by a glycine nitrate process

(In+Nb) co-doped TiO2 nanoparticles with very low dopant concentrations were prepared using a glycine nitrate process. A pure rutile—TiO2 phase with a dense microstructure and homogeneous dispersion of dopants was achieved. By doping TiO2 with 1.5% (In+Nb) ions, a very high dielectric permittivity of ε′=42,376 and low loss tangents of tanδ=0.06 (at room temperature) were achieved. The large conduction activation energy at the grain boundary decreased with decreasing dopant concentration. The colossal permittivity was primarily attributed to the internal barrier layer capacitor (IBLC) effect. The dominant effect of interfacial polarization at the non–Ohmic sample–electrode contact was observed when the dopant concentration was ≤1.0mol%. Interestingly, the sample–electrode contact and resistive–outer surface layer effects, i.e., surface barrier layer capacitor (SBLC) effect, has also an effect on the colossal dielectric response in (In+Nb) co-doped TiO2 ceramics.

Regularities of Impact Failure of Epoxy Composites with Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Microfiller and their Analysis on the Basis of External Surface Layer Concept

Impact toughness of epoxy composite materials reinforced with Al2O3 microparticles of various concentrations were investigated. It is shown that the external (outer) surface layers that form around disperse filler particles is one of the factor responsible their mechanical properties.

Improving the surface quality and mechanical properties by shot-peening of 17-4 stainless steel fabricated by additive manufacturing

Direct metal laser sintering (DMLS), a type of additive manufacturing (AM) process, is currently used for the direct fabrication of powder-based functional metallic objects. The main concern in industrial application of DMLS is the range of materials that can be processed while ensuring that the resulting surface roughness and mechanical properties are equivalent to or better than those of wrought materials. This paper presents an attempt at inducing grain refinements through a shot-peening (SP) process creating severe plastic deformation at the outer surface layers to improve the physical and mechanical properties of 17-4 stainless steel components produced by DMLS. The as-built sample exhibited high content of retained austenite and the SP treatment induces a martensitic phase transformation; the micro-strain and compressive residual stresses were significantly increased upon SP. Compared to an as-built sample, a shot-peened sample exhibited a refined surface microstructure and more favorable roughness, hardness, compressive yield strength, and wear resistance, because of the obtained very fine microstructure. We believe that with the use of SP technology presented in this study, the use of AM materials for a wide range of potential applications should significantly increase for improving their performance. This can highlight the efficiency and applicability of the SP treatment to practical cases.

Spacer fabric-based exuding wound dressing – Part II: Comparison with commercial wound dressings

In this study, a three-layered composite structure based on spacer fabric was designed for absorbent wound dressings. The fabrication and selection of spacer fabrics were discussed in Part I. In this part, two selected spacer fabrics were further modified by covering a polyurethane or a polystyrene electrospun nanofibrous membrane onto their outer layer surface to form the final spacer fabric-based dressing products. In order to confirm the performance of these new spacer fabric-based dressings, the comparisons were conducted with three types of commercial wound dressings. The comparison indicators included the water contact angle, wettability, absorbency, air permeability and water vapor transmission rate. The results showed that in addition to very good water vapor and air permeability, the developed spacer fabric-based dressings had better absorbing properties than commercial foam dressings. Furthermore, their wettability was also good for application as wound dressings. The study has paved a new way to produce advanced wound dressings using three-dimensional textile structures.

Barium isotope fractionation during witherite (BaCO3) dissolution, precipitation and at equilibrium

This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25°C in 10−2M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor αwitherite-fluid is calculated to be 0.99993±0.00004 (or Δ137/134Bawitherite-fluid≈−0.07±0.04‰, 2sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral–fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite–fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed.

Enzyme-Degradable Hybrid Polymer/Silica Microbubbles as Ultrasound Contrast Agents.

The fabrication of an enzyme-degradable polymer/silica hybrid microbubble is reported that produces an ultrasound contrast image. The polymer, a triethoxysilane end-capped polycaprolactone (SiPCL), is used to incorporate enzyme-degradable components into a silica microbubble synthesis, and to impart increased elasticity for enhanced acoustic responsiveness. Formulations of 75, 85, and 95 wt % SiPCL in the polymer feed produced quite similar ratios of SiPCL and silica in the final bubble but different surface properties. The data suggest that different regions of the microbubbles were SiPCL-rich: the inner layer next to the polystyrene template core and the outer surface layer, thereby creating a sandwiched silica-rich layer of the bubble shell. Overall, the thickness of the microbubble shell was dependent on the starting TEOS concentration and the reaction time. Despite the layered structure, the microbubble could be efficiently degraded by lipase enzyme, but was stable without enzyme. The ultrasound contrast showed a general trend of increase in image intensity with SiPCL feed ratio, although the 95 wt % SiPCL bubbles did not produce a contrast image, probably due to bubble collapse. At higher normalized peak negative acoustic pressure (mechanical index, MI), a nonlinear frequency response also emerges, characterized by the third harmonic at around 3f0, and increases with MI. The threshold MI transition from linear to nonlinear response increased with decrease in SiPCL.