Assessment of collagen fibril spacing in relation to selected region of interest (ROI) on electron micrographs--application to the mammalian corneal stroma

AIMS: To evaluate measurements of collagen fibril spacing using different shaped regions of interest (ROI) on transmission electron micrograph (TEM) images of rabbit corneal stroma. METHODS: Following glutaraldehyde fixation and phosphotungstic acid staining, TEM images of collagen fibrils in cross section were projected at a final magnification close to 250,000 × to obtain overlays. Interfibril distances (IFDs; center‐to‐center spacing) were measured within different ROIs of the same nominal area (0.25 μm²) but different shape (with the length to width, L:W, ratio from 1:1 to 6:1). The IFD distribution was analyzed, and the 2D organization assessed using a radial distribution analysis. RESULTS: The fibrils had an average diameter of 35.3 ± 3.8 (SD) nm, packing density of 393 ± 4 fibrils / μm² and a fibril volume fraction of 0.39 ± 0.02. IFDs ranged from 29 to 1400 nm depending on the shape of the ROI, with average values ranging from 263 to 443 nm. By artificially selecting IFD data only to a radial distance of 250 nm, the average IFDs were just 145–157 nm. The radial distributions, to 250 nm, all showed a nearest neighbors first peak which shifted slightly from predominantly at 45–54 nm with more rectangular ROIs. The radial distribution profiles could be shown to be statistically different if the ROI L:W ratio was 2:1 or greater. CONCLUSION: Selection of an ROI for assessment of packing density and interfibril distances should be standardized for comparative assessments of TEMs of collagen fibrils. Microsc. Res. Tech., 2011. © 2011 Wiley‐Liss, Inc.     

Fluorescence relaxation in 3D from diffraction-limited sources of PAGFP or sinks of EGFP created by multiphoton photoconversion

The relaxation of fluorescence from diffraction‐limited sources of photoactivatable green fluorescent protein (PAGFP) or sinks of photobleached enhanced GFP (EGFP) created by multiphoton photo‐conversion was measured in solutions of varied viscosity (η), and in live, spherical Chinese hamster ovary (CHO) cells. Fluorescence relaxation was monitored with the probing laser fixed, or rapidly scanning along a line bisected by the photoconversion site. Novel solutions to several problems that hamper the study of PAGFP diffusion after multiphoton photoconversion are presented. A theoretical model of 3D diffusion in a sphere from a source in the shape of the measured multiphoton point‐spread function was applied to the fluorescence data to estimate the apparent diffusion coefficient, D_ap. The model incorporates two novel features that make it of broad utility. First, the model includes the no‐flux boundary condition imposed by cell plasma membranes, allowing assessment of potential impact of this boundary on estimates of D_ap. Second, the model uses an inhomogeneous source term that, for the first time, allows analysis of diffusion from sources produced by multiphoton photoconversion pulses of varying duration. For diffusion in aqueous solution, indistinguishable linear relationships between D_ap and η⁻¹ were obtained for the two proteins: for PAGFP, D_aq= 89 ± 2.4 μm² s⁻¹ (mean ± 95% confidence interval), and for EGFP D_aq= 91 ± 1.8 μm² s⁻¹. In CHO cells, the application of the model yielded D_ap= 20 ± 3 μm² s⁻¹ (PAGFP) and 19 ± 2 μm² s⁻¹ (EGFP). Furthermore, the model quantitatively predicted the decline in baseline fluorescence that accompanied repeated photobleaching cycles in CHO cells expressing EGFP, supporting the hypothesis of fluorophore depletion as an alternative to the oft invoked ‘bound fraction’ explanation of the deviation of the terminal fluorescence recovery from its pre‐bleach baseline level. Nonetheless for their identical diffusive properties, advantages of PAGFP over EGFP were found, including an intrinsically higher signal/noise ratio with 488‐nm excitation, and the requirement for ∼1/200th the cumulative light energy to produce data of comparable signal/noise.     

Cryo-FIB-nanotomography for quantitative analysis of particle structures in cement suspensions

Cryo‐FIB‐nanotomography is a novel high‐resolution 3D‐microscopy technique, which opens new possibilities for the quantitative microstructural analysis of complex suspensions. In this paper, we describe the microstructural changes associated with dissolution and precipitation processes occurring in a fresh cement paste, which has high alumina and sulphate contents. During the first 6 min, precipitation of ettringite leads to a general decrease of the particle size distribution. In the unhydrated cement paste almost no particles smaller than 500 nm are present, whereas after 6 min this size class already represents 9 vol%. The precipitation of ettringite also leads to a significant increase of the particle number density from 0.294*10⁹/mm³ at t_0min to 20.55*10⁹/mm³ at t_6min. Correspondingly the surface area increases from 0.75 m²/g at t_0min to 2.13 m²/g at t_6min. The small ettringite particles tend to form agglomerates, which strongly influence the rheological properties. The particular strength of cryo‐FIB‐nt is the potential to quantify particle structures in suspension and thereby also to describe higher‐order topological features such as the particle–particle interfaces, which is important for the study of agglomeration processes.     

Measurement of geometrical parameters in cocontinuous polymer blends: 3D versus 2D image analysis

Formulae of stereology are used to estimate 3D geometrical parameters of cocontinuous structures measured from 2D micrographs of polymer blends. 3D images of symmetric and nonsymmetric polymer blends made of fluorescently labelled polystyrene and styrene‐ran‐acrylonitrile copolymer were obtained with laser scanning confocal microscopy. Geometrical parameters of the blend interface, specifically volume fraction, surface area per unit volume (S _V ) and average of local mean curvature were measured directly from the 3D images and compared to the values estimated from analysis of a number of 2D slices combined with stereological relations. When the total length of phase boundary considered in the analysis of the 2D slices (L_Tot ) was at least 6000 times bigger than the characteristic length of the microstructure (S^?1_V ), the standard deviation for all the parameters measured became negligible. However, considerable discrepancies between the average values computed from 3D and 2D images were observed for any value of L_Tot . The mean curvature distribution was also measured from both the 3D images and the 2D slices. The distribution was estimated from the 2D slices but with a width about 2.4 times that of the true value obtained from the 3D images.     

Strengthening caused by power law creep deformation of dispersed particles in an elastic matrix

The interaction energy is approximated between an edge dislocation and a particle deformable by power law creep in an elastic matrix. The stress required to overcome the interaction energy barrier is found to be greater than the Orowan stress, and the dislocation bulges to escape the particle. If the ratio of the shear modulus of the matrix to the viscosity of the particle (μt^m/σ₀) is large, the stress required to climb over the particle is larger than the Orowan stress and the dilocation bulges before it climbs. It is concluded that even if the particle is soft enough to exhibit creep, the strengthening of alloys can be achieved by an Orowan mechanism. The critical resolved shear stress (CRSS) of Cu-B₂O₃, obtained experimentally by Onaka et al. [11], agrees closely with that obtained in our analysis. This supports our analysis that the strength of Cu-B₂O₃ alloy at high temperature may be accounted for by the Orowan mechanism and the attraction between a dislocation and viscous particles. The energy and the force to overcome the energy barrier increases significantly with decrease of m, the strain rate exponent associated with the power law creep particle. It is found through analysis that for m < 1.0 and for certain values of μt^m/σ₀ > 1, the particle repulses the dislocation, while for m = 1.0 and for all values of μt^m/σ₀ > 1, the particle attracts the dislocation, which is the expected interaction between an elastic particle and a dislocation in an elastic matrix.     

An improved strip FRAP method for estimating diffusion coefficients: correcting for the degree of photobleaching

Fluorescence recovery after photobleaching is a widely established method for the estimation of diffusion coefficients, strip bleaching with an associated recovery curve analysis being one of the simplest techniques. However, its implementation requires near 100% bleaching in the region of interest with negligible fluorescence loss outside, both constraints being hard to achieve concomitantly for fast diffusing molecules. We demonstrate that when these requirements are not met there is an error in the estimation of the diffusion coefficient D, either an under‐ or overestimation depending on which assumption is violated the most. We propose a simple modification to the recovery curve analysis incorporating the concept of the relative bleached mass m giving a revised recovery time parametrization τ=m²w²/4πD for a strip of width w. This modified model removes the requirement of 100% bleaching in the region of interest and allows for limited diffusion of the fluorophore during bleaching. We validate our method by estimating the (volume) diffusion coefficient of FITC‐labelled IgG in 60% glycerol solution, D= 4.09 ± 0.21 μm² s^?1 , and the (surface) diffusion coefficient of a green‐fluorescent protein‐tagged class I MHC protein expressed at the surface of a human B cell line, D= 0.32 ± 0.03 μm² s^?1 for a population of cells.     

A simple method to disentangle nanoparticle optical properties by darkfield microspectroscopy

We present a darkfield optical microspectroscopy technique devoted to the disentangled measurement of the absorption and scattering cross sections of nanoparticle (NP) samples with variable concentration. The robustness of the method, including the needed instrumental calibrations, is examined in detail by analyzing and quantifying the major sources of statistic and systematic errors. As an exemplary case, results are presented on a gold NP colloid. The technique takes advantage of a simple inverted microscope, coupled with a spectrograph and equipped with a darkfield condenser and a variable numerical aperture objective to obtain spectra either in darkfield or brightfield optical configurations. By adopting the Lambert–Beer (LB) equation modeling, we were able to disentangle and measure with a single setup the absorption, scattering, and extinction coefficients of the same sample by combining three spectra, obtained by opportunely varying the objective numerical aperture. Typical plasmonic resonances were recognized at approximately 520 and 750 nm. Optical coefficients were measured as a function of particle number density (0.04–3.94 µm^?3, corresponding to 40 µM–4 mM nominal Au concentration) and good linearity was verified up to ～1.5 µm^?3 (～1 mM Au). Moreover, extinction and scattering cross sections were quantified and the validity of the LB approximation was reviewed. Besides its applications to plasmonic NPs, this method may be appropriate for any colloid, provided there exists a characteristic spectral feature in the ultraviolet‐visible‐near infrared range. This technique may be exploited to localize NPs in biological samples. Microsc. Res. Tech. 77:886–895, 2014. © 2014 Wiley Periodicals, Inc.     

An automatic system for controlling the UV-radiation dose

A photodetector based on an ⁺-GaAs/n-ClInPc heterojunction, photosensitive in the 200- to 1000-nm wavelength range, is described. The ClInPc absorbtance is high:K _λ=2×10⁷ m⁻¹ for λ=220 and 380 nm. The photosensitivity of the photodetector is 2250 V/W (S=1 cm²). An automatic system for controlling the UV-radiation dose was developed on the basis of this photoreceiver.     

Electrolyte Jet Machining (EJM) of antibacterial surfaces

Electrolyte Jet Machining (EJM) has been performed on stainless steel surfaces with the aim of reducing bacterial retention through the generation of nanoscale surface morphology. Following initial EJM experiments aimed at investigating the influence of machining depth, machining speed and current density on the resulting surface roughness, three characteristic surfaces were produced with a current density of 10–18 A/cm² and a machining speed of 0.8–8 mm/s to obtain an arithmetic mean height (S_a) of 0.5–0.74 μm and a density of peaks (S_pd) of 0.25–1.26 μm⁻¹. Relatively large differences between the three surfaces in terms of S_pd allowed thorough investigation into the effects of surface feature size on bacterial retention to be performed. Reductions in the order of 90% compared to control samples were achieved for gram-positive Bacillus cereus and Staphylococcus aureus across the entire tested parameter range (S_pd = 0.25–1.26 μm⁻¹), while reductions in the order of 99% were achieved for gram-negative Escherichia coli and Pseudomonas aeruginosa for surfaces characterized by S_pd > 1 μm⁻¹. Not only do the results call attention to EJM as an innovative technology for producing antibacterial surfaces, they also highlight important differences in the behavior of gram-positive and gram-negative bacteria in relation to EJM-textured surfaces with nanoscale surface morphology.     

Specimen preparation technique for high resolution transmission electron microscopy studies on model supported metal catalysts

A new technique is described which can be used for preparing transmission electron microscopy (TEM) specimens suitable for high resolution studies on supported metal catalysts. By conventional silicon processing techniques 200 × 200 μm² Si₃N₄ membranes on Si wafers are produced. These membranes are extremely flat and have a uniform thickness of 13 nm. They can be used as a support in various kinds of thin film deposition. A TiO₂ film, optimally structured with respect to the requirements for high resolution TEM work in TiO₂–metal cluster systems, is deposited on the Si₃N₄ layer. It consists of one monolayer of 10–25 nm TiO₂ crystallites. TiO₂ lattice images show that a line resolution down to 0.19 nm is possible. Examples of TiO₂–Pd and TiO₂–Rh are given using respectively photodeposition and impregnation reduction to produce l.5–4 nm metal clusters.     

New Sulfide Addition Agents for Lubricant Materials

Two sulfides, AsSbS₄, and AsAsS₄ were prepared by aqueous precipitation methods. Property studies covered lubricant characteristics, and comparisons were made with As₂S₃, As₂S₃, Sb₂S₃ and Sb₂S₃. The various compounds were examined as chemical addition agents for diester lubricating grease and organic resin solid film lubricants. Details are presented for lubricant formulation and preparation, as well as laboratory test methods. The single most significant result is the dual response of AsSbS₄ to steel-steel and steel-molybdenum. Previous studies have shown that sulfur compounds as a class are preferential lubricants for molybdenum; however, a lubricating effect for steel by metallic sulfides has been essentially limited to MoS₂.     

Tribological properties of solid lubricants (graphite,Sb2S3, MoS2) for automotive brake friction materials

The effect of three different solid lubricants (graphite, Sb₂S₃, and MoS₂) in the brake friction material on various aspects of friction characteristics was investigated. Three friction material specimens were produced based on an experimental formulation, and they contained 10 vol.% graphite, 7 vol.% graphite + 3 vol.% Sb₂S₃, and 7 vol.% graphite + 3 vol.% MoS₂, respectively, fixing the composition of other ingredients. Tribological properties of the friction materials were obtained using a brake dynamometer. Results showed that the friction materials containing Sb₂S₃ and graphite improved friction stability and fade resistance. The friction materials with Sb₂S₃ and MoS₂, on the other hand, exhibited disadvantages in terms of wear resistance, anti-fading, and DTV (disk thickness variation) generation.     

3D‐quantum interferometer using silicon microring‐embedded gold grating circuit

A 3D (three‐dimensional) quantum interferometer consisting of a silicon microring circuit proposed. The interferometer based on the electron spin cloud projections generated by microring‐embedded gold grating. The electron cloud oscillations result from the excitation of the gold grating at the center of the silicon microring by the dark soliton pulse of 1.50 μm center wavelength. The electron cloud spin‐down, spin‐up automatically formed in the two axes (x, y, respectively) and propagated along the z‐axis. In this proposal, the sensing mechanism of the circuit is manipulated by varying the reflector gold lengths of the sensing arm. The electron cloud spin coupled and changed by changing the gold lengths. The sensitivity measurement of the 3D quantum interferometer for three gold layer lengths of 100 nm, 500 nm, and 1,000 nm is (47.62 nm fs^?1, ±0.4762 fs^?1, ±0.01 nm^?1), (238.10 nm fs^?1, ±0.4762 fs^?1, ±0.002 nm^?1), (476.20 nm fs^?1, ±0.4762 fs^?1, ±0.001 nm^?1), respectively. The used circuit parameters are the real ones that can be fabricated by the currently available technology. Moreover, the silicon micro ring circuit acts as a plasmonic antenna, which can apply for wireless quantum communication. The electron cloud spin projection space–time control can apply for quantum cellular automata.     

Pressure Dependence of Shear Strengths of Thin Films on Metal Surfaces Measured in Ultrahigh Vacuum

The friction coefficient is measured for systems consisting of a thin potassium chloride film deposited onto a variety of clean, flat metal substrates, namely Pb, Sn, Au, Ag, Cu, Pd, Fe, Ta, and two types of steel, which are rubbed by a tungsten carbide pin in an ultrahigh vacuum. The friction coefficients are plotted versus 1/H _S, the inverse of the substrate hardness, where two regimes are found. In the first regime, where deformation at the asperity tips is suggested to be plastic, the observed variation in friction coefficient with substrate hardness is rationalized by assuming that the shear strength S for sliding on a KCl film varies with contact pressure P as S = S ₀ + aP, yielding values for a of 0.14 ± 0.02 and S ₀ of ~60–70 MPa. In the second regime, it is proposed that the softer, film-covered Pb and Sn substrates are closer to being in conformal contact with the rough tribopin. These values of S ₀ and a, along with the measured surface asperity height distribution of the tribopin and the value of the friction coefficient for a KCl monolayer on the metal, are used to rationalize the observed increase in friction coefficient with increasing film thickness.     

Acute effects of splint immobilization of the forearm on in vivo microcirculation and histomorphology of the human skin

BACKGROUND: Splint immobilization of the forearm is often performed in clinical practice. Previous studies investigated the effect of immobilization on bone, cartilage, muscle, and tendon, however, the acute effects on human skin microcirculation and histomorphology remains elusive. METHODS: In 12 healthy, nonsmoking individuals (aged 29.7 ± 9.1 years) a randomly selected forearm was immobilized by splinting for 72 h, whereas the other forearm served as control. In vivo Reflectance‐Mode Confocal‐Microscopy (RMCM) was performed prior (baseline value) and postimmobilization to evaluate: quantitative blood cell flow; density of functional dermal capillaries; epidermal thickness; and granular cell size. RESULTS: At 72h forearm immobilization, quantitative blood cell flow was significantly reduced (42.86 ± 3.68 cells/min) compared to the control blood flow (53.11 ± 3.68 cells/min, P < 0.05) and dermal capillaries indicates less functional density (5.73 ± 0.63 capillaries/mm²) compared to the controls (7.04 ± 0.81 capillaries/mm², P < 0.05). Histometric assessment reveals significantly thinner epidermis following immobilization compared to the control site (40.02 ± 2.91 vs. 46.64±3.09 µm, P < 0.05). Granular cell size was significantly altered at 72 h splinting (730.1 ± 42.53 µm²) compared to the control cell size at 770.2 ± 38.21 µm². Comparison of baseline values of both forearms indicate statistically insignificance (P > 0.05) for each parameter. CONCLUSION: At 72 h splint immobilization, for the first time, significant adaptive mechanisms were evaluated on human skin microcirculation and histomorphology using in vivo RMCM. These adaptations may be considered as an incipient atrophy of the human skin. Long‐term effects of immobilization including the regenerative potential should be evaluated in further RMCM studies. Microsc. Res. Tech. 77:99–103, 2014. © 2013 Wiley Periodicals, Inc.     

Effect of heat treatment on the microstructure and properties of Ni based soft magnetic alloy

A Ni‐based alloy was heat treated by changing the temperature and ambient atmosphere of the heat treatment. Morphology, crystal structure, and physical performance of the Ni‐based alloy were characterized via SEM, XRD, TEM, and PPMS. Results show that due to the heat treatment process, the grain growth of the Ni‐based alloy and the removal of impurities and defects are promoted. Both the orientation and stress caused by rolling are reduced. The permeability and saturation magnetization of the alloy are improved. The hysteresis loss and coercivity are decreased. Higher heat treatment temperature leads to increased improvement of permeability and saturation magnetization. Heat treatment in hydrogen is more conducive to the removal of impurities. At the same temperature, the magnetic performance of the heat‐treated alloy in hydrogen is better than that of an alloy with heat treatment in vacuum. The Ni‐based alloy shows an excellent magnetic performance on 1,373 K heat treatment in hydrogen atmosphere. In this process, the µ_m, B_s, P_u, and H_c of the obtained alloy are 427 mHm^?1, 509 mT, 0.866 Jm^?3, and 0.514 Am^?1, respectively. At the same time, the resistivity of alloy decreases and its thermal conductivity increases in response to heat treatment.     

Local burn versus local cold induced acute effects on in vivo microcirculation and histomorphology of the human skin

Background: The impact of burns and colds on human skin microcirculation and histomorphology has not been compared as yet. Reflectance confocal microscopy (RCM) enables in vivo insight in human skin on cellular and subcellular levels. We evaluated analogies and differences of thermal injuries on microcirculation and histomorphology in vivo using RCM. Methods: Local superficial burn (6 female, 4 male; aged 28.4 ± 2.9 years, burn group) versus superficial cold (4 female, 6 male; aged 30.4 ± 5.2 years, cold group) was induced on the dorsum of the hand in an experimental immersion hand model. In vivo RCM was performed prior (control), immediately (t1) and 15 minutes (t2) following thermal injury to evaluate: Individual blood cell flow (IBCF), functional capillary density (FCD), epidermal thickness (ET), and granular cell size (GCS). Results: In the burn group, IBCF was increased at t1 (78.02 ± 2.60/min) and remained elevated at t2 (84.16 ± 3.04/min). In the cold group, IBCF decreased at t1 (12.62 ± 2.12 min) and increased at t2 (74.24 ± 3.14/min, P < 0.05) compared to the controls (58.23 ± 3.21/min). FCD was 6.74 ± 0.52/mm² in controls and increased at both t1 (7.82 ± 0.72/mm²) and t2 (8.02 ± 0.81/mm²) in the burn group. In the cold group, FCD decreased at t1 (2.60 ± 0.42/mm²) and increased at t2 (7.92 ± 0.44/mm², P < 0.05). ET increased at both t1 (43.12 ± 4.08 μm, P > 0.05) and t2 (47.26 ± 4.72 μm, P < 0.05) in the burn group. In the cold group, ET decreased at t1 (39.92 ± 3.14 μm, P > 0.05) and increased at t2 (44.72 ± 4.06 μm, P < 0.05) compared to the controls (41.26 ± 3.82 μm). Control GCS was 726.9 ± 59.4 μm² and increased at both t1 (739.8 ± 69.8 μm², P > 0.05) and t2 (762.6 ± 71.4 μm², P < 0.05) in the burn group. In the cold group, GCS decreased at t1 (712.4 ± 53.8 μm², P > 0.05) and increased at t2 (742.6 ± 64.8 μm², P < 0.05). Conclusions: Superficial burn induces more cellular destruction and cold leads to huge fluctuation in tissue perfusion, however, with moderate impact on histomorphology. The effect on dermal capillaries suggests a selective neural control and cold injuries might down‐regulate this system, much more than burns can activate it. Microsc. Res. Tech., 2011. © 2011 Wiley‐Liss, Inc.     

Biotinylated vanadium and chromium sulfide nanoparticles as probes for colocalization of membrane proteins

We report the microemulsion synthesis of vanadium and chromium sulfide nanoparticles (NPs) and their biological application as nanoprobes for colocalization of membrane proteins. Spherical V₂S₃ and Cr₂S₃ NPs were prepared in reverse microemulsion droplets, as nanoreactors, obtained by the surfactant sodium bis(2‐ethylhexyl) sulfosuccinate (AOT) in nonpolar organic phase (heptane). Electron microscopic data indicated that the size distribution of the nanoparticles was uniform with an average diameter between 3 ÷ 5 nm. The prepared hydrophobic nanocrystals were transferred in aqueous phase by surface cap exchange of AOT with biotin‐dihydrolipoic ligands. This substitution allows the nanoparticles solubility in aqueous solutions and confer their bioactivity. In addition, we report the conjugation procedure between α‐Lipoic acid (LA) and biotin (abbreviated as biotin‐LA). The biotin‐LA structure was characterized by 1D and 2D NMR spectroscopy. The biotinylated vanadium and chromium sulfide nanoparticles were tested as probes for colocalization of glutamate receptors on sodium‐dodecyl‐sulfate‐digested replica prepared from rat hippocampus. The method suggests their high labeling efficiency for study of membrane biological macromolecules. Microsc. Res. Tech. 79:799–805, 2016. © 2016 Wiley Periodicals, Inc.     

Influence of nanostructure composition on its morphometric characterization by different techniques

Morphometric characterization of nanoparticles is crucial to determine their biological effects and to obtain a formulation pattern. Determining the best technique requires knowledge of the particles being analyzed, the intended application of the particles, and the limitations of the techniques being considered. The aim of this article was to present transmission (TEM) and scanning (SEM) electron microscopy protocols for the analysis of two different nanostructures, namely polymeric nanoemulsion and poly(lactic‐co‐glycolic acid) (PLGA) nanoparticles, and to compare these results with conventional dynamic light scattering (DLS) measurements. The mean hydrodynamic diameter, the polydispersity index, and zeta potential of the nanostructures of polymeric nanoemulsion were 370.5 ± 0.8 nm, 0.133 ± 0.01, and ?36.1 ± 0.15 mV, respectively, and for PLGA nanoparticles were 246.79 ± 5.03 nm, 0.096 ± 0.025, and ?4.94 ± 0.86 mV, respectively. TEM analysis of polymeric nanoemulsion revealed a mean diameter of 374 ± 117 nm. SEM analysis showed a mean diameter of 368 ± 69 nm prior to gold coating and 448 ± 70 nm after gold coating. PLGA nanoparticles had a diameter of 131 ± 41.18 nm in TEM and 193 ± 101 nm in SEM. Morphologically, in TEM analysis, the polymeric nanoemulsions were spherical, with variable electron density, very few showing an electron‐dense core and others an electron‐dense surface. PLGA nanoparticles were round, with an electron‐lucent core and electron‐dense surface. In SEM, polymeric nanoemulsions were also spherical with a rough surface, and PLGA nanoparticles were round with a smooth surface. The results show that the “gold standards” for morphometric characterization of polymeric nanoemulsion and PLGA nanoparticles were, respectively, SEM without gold coating and TEM with negative staining. Microsc. Res. Tech. 77:691–696, 2014. © 2014 Wiley Periodicals, Inc.     

Improving the Tribological Behavior of Graphite/Cu Matrix Self-Lubricating Composite Contact Strip by Electroplating Zn on Graphite

Studies to explore the nature of friction, and in particular thermally activated friction in macroscopic tribology, have lead to a series of experiments on thin coatings of molybdenum disulfide. Coatings of predominately molybdenum disulfide were selected for these experiments; five different coatings were used: MoS₂/Ni, MoS₂/Ti, MoS₂/Sb₂O₃, MoS₂/C/Sb₂O₃, and MoS₂/Au/Sb₂O₃. The temperatures were varied over a range from −80 °C to 180 °C. The friction coefficients tended to increase with decreasing temperature. Activation energies were estimated to be between 2 and 10 kJ/mol from data fitting with an Arrhenius function. Subsequent room temperature wear rate measurements of these films under dry nitrogen conditions at ambient temperature demonstrated that the steady-state wear behavior of these coatings varied dramatically over a range of K = 7 × 10⁻⁶ to 2 × 10⁻⁸ mm³/(Nm). It was further shown that an inverse relationship between wear rate and the sensitivity of friction coefficient with temperature exists. The highest wear-rate coatings showed nearly athermal friction behavior, while the most wear resistant coatings showed thermally activated behavior. Finally, it is hypothesized that thermally activated behavior in macroscopic tribology is reserved for systems with stable interfaces and ultra-low wear, and athermal behavior is characteristic to systems experiencing gross wear.