Search

A technique based on the metal magnetic memory (MMM) is developed to evaluate the contact damage of ferromagnetic materials under nonferromagnetic and ferromagnetic indenters by measuring the magnetic flux leakage (MFL) signals. Great difference between the MFL signals for the ferromagnetic indenter and non-ferromagnetic indenter is experimentally observed. The normal signal shows a dip in the contact region for the ferromagnetic indenter but an increase for the non-ferromagnetic indenter; the tangential signal experiences a peak-peak change through zero in the contact region for the ferromagnetic indenter but a peak for the non-ferromagnetic indenter. Furthermore, the amplitude of MFL signals for the ferromagnetic indenter is considerably larger than that for the non-ferromagnetic indenter. The mechanism of the signal variation is analyzed by considering the magnetic-stress coupling effect. Criteria of the early contact damage are developed based on the variations of the MFL signals and their gradients; and the evaluation parameters are extracted.

A microneedle (MN) array is a novel biomedical device adopted in medical applications to pierce through the stratum corneum while targeting the viable epidermis and dermis layers of the skin. Owing to their micron-scale dimensions, MNs can minimize stimulations of the sensory nerve fibers in the dermis layer. For medical applications, such as wound healing, biosensing, and drug delivery, the structure of MNs significantly influences their mechanical properties. Among the various microfabrication methods for MNs, fused deposition modeling (FDM), a commercial 3D printing method, shows potential in terms of the biocompatibility of the printed material (polylactic acid (PLA)) and preprogrammable arbitrary shapes. Owing to the current limitations of FDM printer resolution, conventional micron-scale MN structures cannot be fabricated without a post-fabrication process. Hydrolysis in an alkaline solution is a feasible approach for reducing the size of PLA needles printed via FDM. Moreover, weak bonding between PLA layers during additive manufacturing triggers the detachment of PLA needles before etching to the expected sizes. Furthermore, various parameters for the fabrication of PLA MNs with FDM have yet to be sufficiently optimized. In this study, the thermal parameters of the FDM printing process, including the nozzle and printing stage temperatures, were investigated to bolster the interfacial bonding between PLA layers. Reinforced bonding was demonstrated to address the detachment challenges faced by PLA MNs during the chemical etching process. Furthermore, chemical etching parameters, including the etchant concentration, environmental temperature, and stirring speed of the etchant, were studied to determine the optimal etching ratio. To develop a universal methodology for the batch fabrication of biodegradable MNs, this study is expected to optimize the conditions of the FDM-based fabrication process. Additive manufacturing was employed to produce MNs with preprogrammed structures. Inclined MNs were successfully fabricated by FDM printing with chemical etching. This geometrical structure can be adopted to enhance adhesion to the skin layer. Our study provides a useful method for fabricating MN structures for various biomedical applications.

For enhancing the 2.0 μm band fluorescence of Ho3+, a certain amount of WO3 oxide was introduced into Ho3+/Tm3+/Yb3+ tri-doped tellurite glass prepared using melt-quenching technique. The prepared tri-doped tellurite glass was characterized by the absorption spectra, fluorescence emission and Raman scattering spectra, together with the stimulated absorption, emission cross-sections and gain coefficient. The research results show that the introduction of WO3 oxide can further improve the 2.0 μm band fluorescence emission through the enhanced phonon-assisted energy transfers between Ho3+/Tm3+/Yb3+ ions under the excitation of 980 nm laser diode (LD). Meanwhile, the maximum gain coefficient of Ho3+ at 2.0 μm band reaches about 2.36 cm-1. An intense 2.0 μm fluorescence emission can be realized.

Magnetic memory method (MMM) is a newly developed passive nondestructive testing method, mainly used to detect the ferromagnetic materials. Because of the faster testing speed and the more convenient testing equipment, MMM has attracted many scholars’ attention. This paper designed wide plate tensile specimens without and with a defect to study the influence of stress distributions on magnetic-flux-leakage (MFL) signals. The three-dimensional (3D) MFL signals on the specimen surface along the directions parallel (x-axis) and vertical (y-axis) to the loading direction were measured. Finite element method (FEM) simulation and digital image correlation (DIC) testing were performed as comparison. Then a theoretical model was applied in finite element method (FEM) software to calculate the MFL signals. The experimental results are essentially in agreement with the calculated results. It is shown that the MFL signals on the measuring lines both parallel and vertical to the loading direction are capable of describing the load magnitude and stress inhomogeneity. Besides, the MFL gradient is in agreement with the equivalent stress distribution along the loading direction. The magnitude of MFL gradient vector developed in this paper shows a good correlation with the equivalent stress distribution vertical to the loading direction. Finally, five characterization parameters were extracted to evaluate the stress inhomogeneity.

Er3+/Ce3+ co-doped tellurite glasses with composition of TeO2-GeO2-Li2O-Nb2O5 were prepared using conventional melt-quenching technique for potential applications in Er3+-doped fiber amplifier (EDFA). The absorption spectra, up-conversion spectra and 1.53 µm band fluorescence spectra of glass samples were measured. It is shown that the 1.53 µm band fluorescence emission intensity of Er3+-doped tellurite glass fiber is improved obviously with the introduction of an appropriate amount of Ce3+, which is attributed to the energy transfer (ET) from Er3+ to Ce3+. Meanwhile, the 1.53 µm band optical signal amplification is simulated based on the rate and power propagation equations, and an increment in signal gain of about 2.4 dB at 1 532 nm in the Er3+/Ce3+ co-doped tellurite glass fiber is found. The maximum signal gain reaches 29.3 dB on a 50 cm-long fiber pumped at 980 nm with power of 100 mW. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite glass is a good gain medium applied for 1.53 µm broadband and high-gain EDFA.

Silver nanoparticles (NPs) were embedded into Er 3+ /Yb 3+ codoped tellurite glasses prepared using melt-quenching and subsequent heat-treating techniques, and the influence of heat-treating temperature (300, 330, 360 and 390 °C) on the 1.53 µm fluorescence of Er 3+ under the excitation of 980 nm LD was investigated. The 1.53 µm fluorescence increased with the heat-treating temperature in the investigated temperature range, which is attributed to the enhanced local electric field around Er 3+ induced by localized surface Plasmon resonance (LSPR) effect of silver NPs. Transmission electron microscopy (TEM) images revealed that the low heat-treating temperature (300 °C) is not enough to nucleate and grow the silver NPs, while near-spherical silver NPs with mean diameter ~13 nm were dispersed in glass heat-treated for 6 h at temperature 390 °C. The results indicate that a relatively high heat-treating temperature is beneficial for the formation of silver NPs and in turn the enhancement of 1.53 µm fluorescence in Er 3+ /Yb 3+ codoped tellurite glass.

Ho3 +/Yb3 + codoped zinc-tellurite glasses containing silver nanoparticles (NPs) were prepared using the conventional melt-quenching technique. The detailed effect of silver NPs on the upconversion emission of Ho3 +, thermal stability and structure behavior of glass hosts was investigated from the measured absorption spectra, upconversion emission spectra, differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images. Two frequency upconversion emission bands centered at 546 nm (green) and 657 nm (red) corresponding to Ho3 + transitions of 5F4(5S2) → 5I8 and 5F5 → 5I8, respectively, are simultaneously observed under the 980 nm excitation at room temperature. It is shown that the introduction of silver NPs can further improve the upconversion emissions of Ho 3 + and thermal stability of glass host, while the glass structure maintains the amorphous nature. The enhanced upconversion emission is mainly attributed to the increased local electric field around Ho 3 + induced by localized surface plasmon resonance (LSPR) effect of silver NPs. Furthermore, the energy transfer (ET) mechanism from Yb3 +:2F5/2 level to Ho3 +:5I6 level is quantitatively analyzed by calculating relevant micro- parameters and phonon contribution ratio.

The silver nanoparticles (NPs) was introduced into the Er 3+ /Yb 3+ codoped tellurite glasses with composition of TeO 2 –ZnO to improve the 1.53 µm band fluorescence of Er 3+ and the thermal stability of glass host. The UV–Vis–NIR absorption spectra, 1.53 µm band fluorescence spectra and fluorescence decaying curves, the differential scanning calorimeter (DSC) curves, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images of glass samples were characterized to investigate the effect of silver NPs on the fluorescence properties of Er 3+ , thermal stability and structure behavior of glass host. It is shown that the Er 3+ /Yb 3+ codoped tellurite glass emits intense 1.53 µm band fluorescence with peak wavelength located at about 1532 nm under the 980 nm excitation. The introduction of silver NPs further improves the fluorescence intensity of Er 3+ which is attributed to the enhanced local electric field effect induced by localized surface Plasmon resonance (LSPR) of silver NPs and the possible energy transfer from silver NPs to Er 3+ . An improvement by about 62% of 1.5 3 µm band fluorescence intensity was found in the studied Er 3+ /Yb 3+ codoped tellurite glass containing 0.5 mol% amount of AgNO 3 . In addition, the thermal stability of glass host increases with the introduction of silver NPs while the glass structure maintains the amorphous nature. The present results indicate that the prepared Er 3+ /Yb 3+ codoped tellurite glass with an appropriate amount of silver NPs has good prospect as a gain medium applied for 1.53 µm band broad and high-gain erbium-doped fiber amplifiers (EDFAs).

A model of Er3+-doped chalcogenide glass (Ga5Ge20Sb10S65) microstructured optical fiber (MOF) amplifier under the excitation of 980 nm is presented to demonstrate the feasibility of it applied for 1.53 μm band optical communications. By solving the Er3+ population rate equations and light power propagation equations, the amplifying performance of 1.53 μm band signals for Er3+-doped chalcogenide glass MOF amplifier is investigated theoretically. The results show that the Er3+-doped chalcogenide glass MOF exhibits a high signal gain and broad gain spectrum, and its maximum gain for small-signal input (−40 dBm) exceeds 22 dB on the 300 cm MOF under the excitation of 200 mW pump power. Moreover, the relations of 1.53 μm signal gain with fiber length, input signal power and pump power are analyzed. The results indicate that the Er3+-doped Ga5Ge20Sb10S65 MOF is a promising gain medium which can be applied to broadband amplifiers operating in the third communication window.

Magnetization and magnetostriction are of critical importance to understand the magnetic behavior of ferromagnetic materials under stress and magnetic fields. The micromechanism of magnetization (or magnetostriction) is determined by the probability of angular distribution of magnetic moments and saturation magnetization (or saturation deformation). Thus, the probability of angular distribution of magnetic moments is important to construct the relationship between the magnetization (or magnetostriction) and magnetic moments. In this letter, a new microstatistical model is developed to explain the magnetization and magnetostriction mechanisms for isotropic materials. The probability of angular distribution between magnetic moment and magnetic field is expressed by a modified Boltzmann distribution. The results calculated by the present model are compared with the experimental results. The values of the determination coefficient R 2 indicate that the present model can accurately describe the relationship between magnetization and magnetostriction under both stress and magnetic fields.

A certain amount of WO3 oxide was introduced into the Ho3+/Tm3+ codoped tellurite glass, and the absorption spectra, fluorescence spectra, Raman spectra, X-ray diffraction patterns and differential scanning calorimeter curves were measured to illustrate the enhanced effects of WO3 on the 2 µm fluorescence of Ho3+ and thermal stability of glass host. Under the excitation of 808 nm LD, the 2 µm fluorescence of Ho3+ increases obviously with the partial substitution of TeO2 by WO3 oxide, which is attributed to the enhanced energy transfer process from Tm3+:3F4 to Ho3+:5I7 level by providing a relatively large phonon energy. Meanwhile, the thermal stability of glass host increases accordingly, which is mainly attributed to the formation of thermal stability W=O bond. The intense 2 µm fluorescence together with good thermal stability indicates that Ho3+/Tm3+ codoped WO3 modified tellurite glass is a potential laser glass for efficient 2 µm emission.

New Yb3+/Nd3+/Tm3+ tri-doped tellurite glasses (TeO2–Bi2O3–ZnO–Na2O) with improved thermal stability and intense blue upconversion emission were prepared by melt-quenching technique. The thermal stability and blue upconversion of glass samples were investigated by means of differential scanning calorimeter (DSC) and fluorescent spectrophotometer measurements. DSC results show that the prepared tellurite glasses have favorable thermal stability for fiber drawing and the difference ( Δ T ) between the estimated crystallization onset temperature ( T x ) and the transition temperature ( T g ) reaches about 186 °C, which is larger than that of some other tellurite glass hosts. Under the excitation of 980 nm laser diode (LD), the tri-doped glass samples exhibit an intense blue (~474, 485 nm) upconversion emission, which is attributed to the simultaneous contributions from Tm3+:1G4→3H6 and Nd3+:2G9/2→4I9/2 transitions, and the possible upconversion luminescent mechanism based on the energy transfers from Yb3+ is presented. The above results indicate that the new synthesized Yb3+/Nd3+/Tm3+ tri-doped tellurite glass is a promising candidate applied for the blue solid-state lasers.

A simple immersion approach for fabricating superhydrophobic Mg alloy surfaces is present here. Micro/nanometer-scale rough structures composed of micrometer-scale island-like rough structures and nanometer-scale sheets are generated on the Mg alloy surfaces after immersion in the aqueous CuSO4 solution. After ultrasonic cleaning, the micro/nanometer-scale rough structures are disappeared, whereas the lump-like rough structures appear on the Mg alloy surfaces. After modification with stearic acid, the as-prepared micro/nanometer-scale rough structures and the micrometer-scale lump-like rough structures all show superhydrophobicity. The contact angles of the water droplet on the aforementioned two structures are respectively 151.3° and 161.8°. The rolling angles are respectively 3° and 13°. The results indicate that the cooperation of suitable rough structures and stearic acid modification is responsible for the obtained superhydrophobicity on the Mg alloy surfaces.

The friction and wear properties of Ti6Al4V/WC-Co friction pair were studied using an autonomous atmospheric pressure bare electrode cold plasma jet generating device and block-on-ring friction/wear tester, respectively. The study was conducted under air, air jet, nitrogen jet, air cold plasma jet, and nitrogen cold plasma jet atmospheres. Both nitrogen cold and air cold plasma jets effectively reduced the friction coefficients of the friction pairs and decreased friction temperature. The friction coefficient in the nitrogen cold plasma jet decreased to almost 60% compared with that in the air. The scanning electron microscope, energy-dispersive X-ray spectroscope, and X-ray diffraction analyses illustrated that adhesive wear was relieved and the friction surfaces of Ti6Al4V were smoother, both in the nitrogen cold and air cold plasma jets. The roughness value R a of the Ti6Al4V friction surfaces can reach 1.107 μm. A large number of nitrogen particles in the ionic and excited states contained by cold plasma jets reacts easily on the friction surface to produce a large amount of nitrides, which can excellently reduce the wear of Ti6Al4V/WC-Co friction pairs in real-time.

Silver nanoparticles (NPs) were introduced into the Er 3+ -doped tellurite glasses (TeO 2 –Bi 2 O 3 –TiO 2 ) and their effects on the 1.53 µm band fluorescence of Er 3+ and thermal stability of glass host were investigated. It was found that the presence of silver NPs nucleated and grown during the heat annealing process, could improve the thermal stability and the 1.53 µm band fluorescence. Maximum enhancement in the 1.53 µm band fluorescence was obtained in sample heat-treated for 48 h. However, further increase in the heat annealing time (~72 h) reduces the fluorescence intensity. Enhancement in the 1.53 µm band fluorescence is attributed to the increased local electric field induced by silver NPs whereas the quenching is ascribed to the energy transfer from Er 3+ ions to silver NPs.

Nanocapsules (NCs) are promising candidates for the controlled and targeted delivery of therapeutics in a variety of biomedical applications. In this work we report the formation of NCs by miniemulsion polymerization with renewable, biodegradable, and biocompatible surfactant (lecithin) and hydrophobe (Neobee M5). PMMA was employed as the model (and biocompatible) polymer to synthesize the NCs. Stable dispersions of NCs with sizes between 200-500 nm in diameter and high encapsulation efficiencies were achieved. The effect of the surfactant concentration and mechanical energy input on the size of the parent miniemulsion droplet, and on the resulting NCs was followed by DLS measurements. The final particle morphology was confirmed by SEM and TEM.

In this work we examine the aggregation behavior of ethoxylated copolymer surfactants in 1,1,1,2-tetrafluoroethane in the presence of water, and the ability of such aggregates to uptake a model biomolecule. Our approach consists of developing a rational framework for understanding the behavior of interfacially active species at the HFA134a-water (HFA134a|W) interface using a combination of in situ high-pressure tensiometry, spectroscopy, and small-angle neutron scattering (SANS). The optimum hydrophilic-to-HFA-philic balance (HFB) for the ethylene oxide-propylene oxide-ethylene oxide (EOnPO∼43EOn, where subscripts indicate the number of repeat units) surfactant series at the HFA134a|W interface was determined at 298 K and saturation pressure of the propellant (under pressure). The selection of promising candidates for the reverse aggregate formation studies was based on the tension vs. HFB scan. Tensiometric information revealed that EO3PO43EO3 occupies a very large area per molecule at the HFA134a|W interface, which represents a general trend for compressible solvents that are small and also able to interact with water more favorably than alkane solvents. The water solubilization capacity of the EO3PO43EO3 surfactant was investigated in situ by UV-vis spectroscopy, with a suitable solvatochromic probe. At a surfactant concentration above the determined critical aggregation concentration, a shift in the absorption maximum of the probe towards that of pure water was observed as the water-to-surfactant ratio increases. A similar but more pronounced shift was observed in the presence of a co-solvent. The nature of the aqueous environment associated with the aggregates is discussed based on the spectroscopic results. The microstructure of the aggregates is investigated by SANS. Scattering curves were also used to confirm the uptake of a model protein in the reverse aggregates. The relevance of this work stems from the fact that reverse aggregates of water in HFA134a are potential candidate formulations for the delivery of hydrophilic drugs, including biomolecules, to and through the lungs.

In this work we investigate the ability of biodegradable and biocompatible lactide-based nonionic amphiphiles to stabilize a model drug (salbutamol base) dispersion in hydrofluoroalkane (HFA) propellant. A series of triblock copolymers of the type poly(lactide)-poly(ethylene glycol)-poly(lactide) (LA(m)EO(n)LA(m)) with varying molecular weight (MW) and % EO were synthesized. The cohesive forces between drug particles in liquid HFA in the presence of the amphiphiles were quantitatively determined by colloidal probe microscopy (CPM). The effect of cosolvent, oleic acid, and a nonionic triblock copolymer with the propylene oxide moiety as the HFA-phile was also investigated. CPM results show that the overall concentration, MW, surfactant tail (LA) length, and the ratio between the stabilizing LA moiety and the anchor EO group have a great impact on the drug cohesive forces. The CPM results in liquid HFA were correlated to the bulk physical stability of the drug suspensions in the propellant 1,1,1,2,3,3,3-heptafluoropropane (HFA227). The dispersions in HFA227 were significantly improved in the presence of LA(m)EO(n)LA(m), correlating well with the low cohesive forces determined by CPM. The applicability of LA-based amphiphiles might be extended to other suspension-based formulations provided a suitable headgroup is found. This study is relevant for the development of HFA-based dispersion pressurized metered-dose inhaler formulations.

In this work, we show that nanoparticles (NPs) dispersed in compressible hydrofluoroalkanes (HFAs) at small volume fractions are capable of stabilizing micrometer-sized particle colloids, which otherwise flocculate due to strong van der Waals forces. Water-soluble, biodegradable NPs with a chitosan (CS) core, grafted with highly HFA-philic moieties, can be readily dispersed in the low dielectric HFAs and are capable of imparting stability to a wide range of therapeutic particles having different chemistries (polar or hydrophobic; small and large molecular weight, including peptides and proteins) and morphologies (micronized crystals or amorphous). These NP systems thus serve as a broadly applicable platform for the noninvasive delivery of therapeutics to and through the lungs using propellant-based, portable inhalers, and are also of potential relevance in other industries where HFAs are employed as solvents or propellants. This concept may also be applicable to other compressible solvents.

Molecular organization of Langmuir-Blodgett (LB) monolayers of novel copper-containing metal-ligand surfactants was characterized by the surface-selective vibrational sum frequency generation (SFG) spectroscopy. The orientational and conformational order inferred from the SFG peak amplitudes and line shapes were correlated with the two-dimensional phases of the monolayers observed in the compression isotherms. The octadecyl-pyridin-2-ylmethyl-amine (L(PyC18)) ligand by itself shows good amphiphilic properties, as indicated by the high monolayer collapse pressure at the air/water interface, but its LB films transferred onto fused silica exhibit a high degree of trans-gauche conformational disorder in the alkyl tails. Coordination of copper(II) ions to the chelating head group enhances the molecular alignment and reduces the fraction of gauche defects of the alkyl chains. Monolayers of single-tail (L(PyC18)Cu(II)Cl(2)) and double-tail [(L(PyC18))(2)Cu(II)]Cl(2) metallosurfactants show distinctly different behavior of their molecular organization as a function of the area per molecule. Our observations suggest metal-ligand interactions as a pathway to induce molecular order in LB monolayer films.

Pressurized metered-dose inhalers (pMDIs) have been recognized as potential devices for the delivery of systemically acting drugs, including biomolecules, to and through the lungs. Therefore, the development of novel excipients capable of imparting stability to suspension formulations in hydrofluoroalkane (HFA) propellants is of great relevance because many of the drugs of interest are poorly soluble in HFAs. In this work, we use ab initio calculations and chemical force microscopy (CFM) to determine the HFA-philicity of the biodegradable and biocompatible ester moiety quantitatively. The complementary information obtained from the binding energy calculations and adhesion force measurements are used to gain microscopic insight into the relationship between the chemistry of the moiety of interest and its solvation in HFA. A lactide (LA)-based copolymer surfactant was synthesized and characterized, and its ability to stabilize a dispersion of micronized budesonide in HFA227 was demonstrated. These results corroborate the ab initio calculations and CFM and show that the LA-based moiety is a suitable candidate for enhancing the stability of dispersions in HFA-based pMDIs.

The present Letter reports a simple and effective two-steps immersion method to fabricate superhydrphobic surfaces with high adhesive forces towards water on steel substrates. The steel plates were firstly immersed in the aqueous CuSO 4 solution for 20 s, and then immersed in the stearic acid ethanol solution for 24 h. The sample surfaces were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectrophotometry, X-ray diffraction and optical contact angle measurements. The results show that, after two-steps immersion processes, the cupric stearate microspheres with binary micro/nanometre-scale rough structures are formed on the steel surfaces. The as-prepared steel surfaces exhibit a good high adhesive superhydrophobicity with a 166.3 water contact angle and no rolling angle. The high adhesive superhydrophobic surfaces on steel substrates have a good potential application in no loss liquid transportation.