Micro/nanotribological studies of lanthanum-based thin films on phosphorylated 3-Aminopropyltriethoxysilane self-assembled monolayers

Lanthanum-based phosphonate 3-Aminopropyltriethoxysilane (APTES) thin films were prepared on the hydroxylated silicon substrate by a self-assembling process from formulated solution. The tribological behaviors of APTES-SAM, phosphorylated APTES-SAM and lanthanum-based films were experimentally investigated at the nanoscale using atomic force microscope (AFM) and at the microscale using a UMT-2MT reciprocating friction and wear tester.The nano- and microscale tribological behaviors between the films are compared and discussed. Results showed that the adhesive forces and friction forces increased with the relative humidity. When the applied normal load increased from 0 to 70 nN, the adhesion did not change, but the friction increased linearly. Results generally showed surfaces of the more hydrophobic property revealed the lower adhesion. It was also found that lanthanum-based films that had the highest water contact angle exhibited the lowest adhesion force and friction force and the relative long wear life compared with APTES-SAM and phosphorylated APTES-SAM. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the low work of adhesion of non-polar terminal groups and enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate.     

Effect of shear heating during injection molding on the morphology of PC/LCP blends

Fiber relaxation of liquid crystalline polymer (LCP) in the mold during injection molding was investigated. A blend of LCP and polycarbonate was used. The LCP used, namely LC5000, is a thermotropic LCP consisting of 80% and 20% of hydroxybenzoic acid and ethylene terephthalate, respectively. The filling of the mold and the temperature profile of the melt in the mold, after the mold has been completely filled, were computed using the finite element/finite difference method (FE/FDM). The morphology of the fibers was greatly influenced by the temperature of the different layers in the sample. This was confirmed by scanning electron microscopy (SEM) examination of the injection-molded specimen. When shear heating caused the temperature of the melt to increase above 280 °C, relaxation of the fibers was rapid. This resulted in a final morphology where the LCP existed in short fibers or ellipsoids. It was concluded that the high shear rate, which is needed for fiber deformation, must be accompanied by fast cooling to minimize the effects of shear heating, so that the fibers formed could be retained.     

Synthesis, crystal structure and properties of the new semiconductor (EVT)4·[Pt(CN)4]

A novel radical cation salt based on of the donor (4,5-ethylenedithio-4′,5′-vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN)₄²⁻ has been synthesized: (EVT)₄·[Pt(CN)₄] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with β-packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT)₄·[Pt(CN)₄] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8×10⁻² Ω⁻¹ cm⁻¹ and the temperature dependence of the conductivity exhibits semiconducting character.     

Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Epitaxial and polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi₄Ti₃O₁₂ may be suppressed by the formation of a titanium-rich phase such as Bi₂Ti₂O₇ owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.     

Effect of alkyl side-chain length and solvent on the luminescent characteristics of poly(3-n-alkylthiophene)

In poly(3-n-alkylthiophene) (P3AT), the length of alkyl side chain as well as the solvent used for film casting affected the conformation and eventually the luminescent characteristics of the polymers. When the length of alkyl side chain was shorter than 12 carbon atoms, the electronic absorption and PL spectra of P3AT film showed red shift as the length of the alkyl side chain increased. This is because, when the length of the alkyl side chain is not too long, solvation is promoted with increase in the length of the alkyl side chain, leading to expanded chain structures with longer π-conjugation lengths. Conversely, when the length of the alkyl side chain was longer than 12 carbon atoms, the electronic absorption and PL spectra of P3AT film showed blue shift as the length of the alkyl side chain increased. This is because, when the length of the alkyl side chain is too long, the steric hindrance becomes predominant leading to highly distorted chain conformation with shorter π-conjugation lengths. The PL intensity of the film cast from THF was higher by an order of magnitude than that of the film cast from chloroform, toluene, or p-xylene. In the P3AT films cast from a poor solvent such as THF, the polymer chains are highly distorted leading to high PL intensity due to exciton localization. In the EL spectra of P3AT films cast from various solvents, λ_max shifted as much as 140 nm depending upon the solvent characteristics. This result demonstrates that the color of EL can be varied from blue to orange simply by casting the same polymer from a different solvent.     

Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites

In this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al₂O₃) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al₂O₃)_BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al₂O₃) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al₂O₃)_BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness.     

Effect of Nd doping on the grain-matrix contribution to ac losses in sintered Bi1.6Pb0.4Sr2(Ca1−xNdx)2Cu3Oδ superconductors

We have carried out measurements of complex ac susceptibility χ=χ′+χ″ as a function of temperature and ac field amplitude on rectangular bar-shaped high-temperature superconductors (HTS) with nominal composition of Bi_1.6Pb_0.4Sr₂(Ca_1−xNd_x)₂Cu₃O_δ superconducting samples prepared by the solid-state reaction method. The effect of Nd-substitution on the Bi–(Pb)–Sr–Ca–Cu–O system has been investigated in terms of ac susceptibility study. We estimated the effective volume fraction of the grains and the field dependence of the inter-granular critical current density comparing the maximum of the extracted matrix susceptibility and the corresponding calculated data which was obtained employing the power law critical state model.     

Effect of carbon source on the carbothermal reduction nitridation for synthesis of (Ti, W, Mo, V)(C, N) nanocrystalline powders

The effect of carbon source on the carbothermal reduction-nitridation during synthesizing (Ti, W, Mo, V)(C, N) nanocrystalline powders was investigated. For a systematic comparison, activated carbon, graphite and two kinds of carbon black powder were used as reducing agents in this study. Ultrafine (Ti, W, Mo, V)(C, N) powders with a particle size of ~ 200-500 nm have been produced at 1450 °C for 2 h by using nanosized carbon black source with small particle size. The presence of phases in the reaction products was characterized with X-ray diffraction (XRD) and the microstructure of carbon source powders and final products was studied by scanning electron microscopy (SEM). The results show that the formation of the Ti(C, N) phase is strongly dependent on the particle size of carbon source powders, and the synthesizing temperature of the Ti(C, N) phase decreases significantly from 1750 °C to 1300 °C by using nanosized carbon black, as compared with micron graphite. In addition, activated carbon with a particle size of 5-50 μm does not favor the dissolution of tungsten or molybdenum carbides into Ti(C, N) despite its large specific surface area.