The pH-induced thermosensitive poly (NIPAAm-<Emphasis Type="Italic">co</Emphasis>-AAc-<Emphasis Type="Italic">co</Emphasis>-HEMA)-<Emphasis Type="Italic">g</Emphasis>-PCL micelles used as a drug carrier

The macromonomer of 2-hydroxyethyl methyacrylate-caprolactone (HPCL) was synthesized by the ring-opening polymerization (ROP) of ε-caprolactone, which was initiated by 2-hydroxyethyl methyacrylate (HEMA). Then, the graft terpolymers of NIPAAm-co-AAc-co-HEMA-g-PCL (PHNA-CL) with varying mole ratios were subsequently synthesized by free radical polymerization of HEMA-PCL, N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc). PHNA-CL was further self-assembled in different types of solvent. All the as-prepared copolymers were characterized by ¹H NMR, FT-IR and GPC. Micellization behaviors of micelles were studied by TEM and DLS. The micelles exhibited a phase transition temperature which can be readily adjusted by changing pH value of the micellization system. Micelle loaded with doxorubicin (DOX) was used to evaluate the drug release behavior. The release of DOX from micelles could be controlled by changing pH value and temperature in buffer solutions. The micelles are potentially to be used as a new anticancer drug carrier for intracellular delivery.     

Characterization of poly(ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate-<Emphasis Type="Italic">co</Emphasis>-carbon monoxide)/layered silicate clay hybrids obtained by melt mixing

In recent times, polymer-layered silicate nanocomposites have drawn a great deal of attention because they often exhibit tremendous improvements in material properties compared with virgin polymers or conventional micro- or macro-composites. In the present study, nanocomposites were developed from organically modified clay and poly(ethylene-co-vinyl acetate-co-carbon monoxide) by melt mixing. FTIR spectroscopy reveals that the interaction between the organoclay and EVACO is thermodynamically favored. High resolution wide angle X-ray diffraction and transmission electron microscopy were used to study the morphology of the nanocomposites. Elemental mapping by scanning electron microscopy indicates good dispersion and distribution of the nanoclay in EVACO matrix. The mechanical properties of the nanocomposites are optimum at a clay loading of 3%.     

Body distribution of poly(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide) copolymer degradation products in rats

Poly (d,l-lactide-co-glycolide) (PLGA) copolymers are among the few synthetic polymers approved for human use, but the biocompatibility of PLGA-derived oligomers and particles remains questionable. Here, high molecular weight PLGA (Mw = 32,000) was radiolabeled with ¹²⁵I in chloroform solution, and the body distribution of PLGA copolymer degradation products was examined following subcutaneous implantation of round ¹²⁵I-PLGA films on the back of Sprague Dawley rats. Autoradiographic images of the PLGA implant taken at 2, 4, 6, 8, 10, and 12 weeks revealed that the central portion of the film degraded much more rapidly than the marginal portions. Examination of the body compartment distribution at these time points revealed that over one-half of the radioactivity was recovered from skin. The remaining radioactivity was concentrated in the blood, liver, and kidneys. Radioactivity steadily appeared in the blood and remained elevated up to 12 weeks after implantation, while the liver to kidney distribution began to decrease after 6 weeks. Cumulatively, these results indicate that the clearance of degraded particles and fragments from the implantation site is extremely delayed. Moreover, the degraded particles and fragments were selectively concentrated in the liver and kidneys, following release of degraded products into the bloodstream from the implantation site.     

Synthesis of crosslinked poly(styrene-<Emphasis Type="Italic">co</Emphasis>-divinylbenzene-<Emphasis Type="Italic">co</Emphasis>-sulfopropyl methacrylate) nanoparticles by emulsion polymerization: Tuning the particle size and surface charge density

We have synthesized highly charged, crosslinked poly (styrene-co-divinylbenzene-co-sulfopropyl methacrylate) copolymer colloidal particles using emulsion polymerization. The effects of concentration of the emulsifier and the initiator on the particle size and the charge density of the colloidal particles are studied. Colloidal particle size is highly dependent upon the concentration of the emulsifier and the initiator. The colloidal particle diameter decreases with increasing concentration of the emulsifier and increases with increasing concentration of the initiator in the polymerization mixture. Number of particles, surface charge density and charges per particle are also functions of both the emulsifier and the initiator concentration. The surface charge density and the number of charges per sphere increase with increasing particle diameter. These copolymer colloid particles self assemble readily and diffract visible light. Polymer hydrogel imbibed with these colloids shows the light diffraction.     

Elastomeric electrospun scaffolds of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-trimethylene carbonate) for myocardial tissue engineering

In myocardial tissue engineering the use of synthetically bioengineered flexible patches implanted in the infarcted area is considered one of the promising strategy for cardiac repair. In this work the potentialities of a biomimetic electrospun scaffold made of a commercial copolymer of (l)-lactic acid with trimethylene carbonate (P(l)LA-co-TMC) are investigated in comparison to electrospun poly(l)lactic acid. The P(l)LA-co-TMC scaffold used in this work is a glassy rigid material at room temperature while it is a rubbery soft material at 37°C. Mechanical characterization results (tensile stress–strain and creep-recovery measurements) show that at 37°C electrospun P(l)LA-co-TMC displays an elastic modulus of around 20 MPa and the ability to completely recover up to 10% of deformation. Cell culture experiments show that P(l)LA-co-TMC scaffold promotes cardiomyocyte proliferation and efficiently preserve cell morphology, without hampering expression of sarcomeric alpha actinin marker, thus demonstrating its potentialities as synthetic biomaterial for myocardial tissue engineering.     

Electrospun poly(<Emphasis Type="SmallCaps">d</Emphasis>/<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="SmallCaps">l</Emphasis>-lactide) hybrid matrix: a novel scaffold material for soft tissue engineering

Electrospinning is a long-known polymer processing technique that has received more interest and attention in recent years due to its versatility and potential use in the field of biomedical research. The fabrication of three-dimensional (3D) electrospun matrices for drug delivery and tissue engineering is of particular interest. In the present study, we identified optimal conditions to generate novel electrospun polymeric scaffolds composed of poly-d/l-lactide and poly-l-lactide in the ratio 50:50. Scanning electron microscopic analyses revealed that the generated poly(d/l-lactide-co-l-lactide) electrospun hybrid microfibers possessed a unique porous high surface area mimicking native extracellular matrix (ECM). To assess cytocompatibility, we isolated dermal fibroblasts from human skin biopsies. After 5 days of in vitro culture, the fibroblasts adhered, migrated and proliferated on the newly created 3D scaffolds. Our data demonstrate the applicability of electrospun poly(d/l-lactide-co-l-lactide) scaffolds to serve as substrates for regenerative medicine applications with special focus on skin tissue engineering.     

Impact-ionization-stimulated electroluminescence in isotype <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-AlGaAsSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb heterostructures

We have studied electroluminescence in n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures with isotype heterojunctions, in which the quantum efficiency of emission is increased due to the additional production of electron-hole pairs as a result of the impact ionization that takes place near the heterointerface. The impact ionization in such heterostructures is possible due to the presence of deep wells in the energy band structure.     

Long-wavelength photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

Wear behaviour of Zr-based <Emphasis Type="Italic">in situ</Emphasis> bulk metallic glass matrix composites

Zr-based bulk metallic glass (BMG) and its in situ BMG matrix composites with diameter of 3 mm were fabricated by conventional Cu-mould casting method and the dry sliding wear behaviour of the BMG and composites was investigated. Compared to the pure BMG, the composites exhibited a markedly improved wear resistance from 10 to 48% due to the existence of various volume fractions of the ductile β-Zr dendritic phase embedded in the glassy matrix. The composites showed lower friction coefficient and wear rate than the pure BMG. Meanwhile, the surface wearing of the composite with a proper amount of β-Zr dendrites was less severe compared to that of the pure BMG. The worn surface of the composite was covered with mild grooves and some fine wear debris, which exhibited the characteristic of a mild abrasive wear. The improvement of the wear resistance of the composite with the proper amount of β-Zr crystalline phase is attributed to the fact that the β-Zr crystalline phase distributed in the amorphous matrix has some effective load bearing, plastic deformation and work hardening ability to decrease strain accumulation and the release of strain energy in the glassy matrix, restrict the expanding of shear bands and cracks, and occur plastic deformation homogeneously.     

Graphitization behavior of iodine-treated <Emphasis Type="Italic">Bombyx mori</Emphasis> silk fibroin fiber

In order to investigate the graphitization behavior of Bombyx mori silk fibroin (SF) fibers, structural inspection of carbonized SF fibers treated with iodine vapor was studied at different temperatures, from 800 to 1400 °C. Wide angle X-ray diffraction measurement suggested that both untreated and iodinated SF fibers exhibited amorphous structure carbonized to 1200 °C. After carbonization at 1400 °C for 12 h, a graphite-like structure was obtained. Raman spectroscopy and transmission electron microscopic observation showed that the graphite layers of SF fibers became more ordered after iodine treatment. The carbon yield obtained at higher temperature (1400 °C) after iodine treatment was higher, ca. 28 wt%, than that of untreated SF.     

Speed of sound in <Emphasis Type="Italic">n</Emphasis>-hexane, <Emphasis Type="Italic">n</Emphasis>-octane, <Emphasis Type="Italic">n</Emphasis>-decane,and <Emphasis Type="Italic">n</Emphasis>-hexadecane in the liquid state

This paper describes an improved experimental facility for measuring the speed of sound in liquids with an accuracy of up to 0.1%. Measurements of the speed of sound in liquid n-hexane, n-octane, n-decane, and n-hexadecane at temperatures of 298–433 K and pressures of 0.1–100 MPa have been made. It has been shown that in the possible comparison range the obtained values of the speed of sound are in good agreement with the literature data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 732–736, July–August, 2008.     

High-pressure behavior and Hirshfeld surface analysis of nitrogen-rich materials: triazido-<Emphasis Type="Italic">s</Emphasis>-triazine (TAT) and triazido-<Emphasis Type="Italic">s</Emphasis>-heptazine (TAH)

Triazido-s-triazine (TAT) and triazido-s-heptazine (TAH) are two kinds of effective nitrogen-rich precursors for carbon nitride nanomaterials and potential high-energy density materials. In this work, the high-pressure behavior (0–500 GPa) and Hirshfeld surface of crystalline TAT and TAH were studied in details to better compare and reveal their stabilities. Crystal and molecular structures of TAT and TAH largely changed with the increase in pressure. The distortion of rings happens at 171 GPa for TAT and 483 GPa for TAH. The azide/tetrazole (AZ/TZ) isomerization happens in crystalline TAT, and the tetrazole ring forms at 266 GPa for the first time, while this phenomenon has not been observed in crystalline TAH during the whole process. Hirshfeld surface analyses intuitively show that: (1) both compounds possess the planar conjugated molecular structures; (2) N…N nonbonding interactions contribute a lot to stabilize their crystal packings; and (3) TAH is much more resistant to high pressure and more stable than TAT. The systematic investigation gives a guidance to understand the physical and chemical behaviors of nitrogen-rich azidoheterocyclic materials.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

Ductile-<Emphasis Type="Italic">to</Emphasis>-brittle transition in cenosphere-filled polypropylene composites

Cenosphere-filled polypropylene (PP) composites were fabricated and characterized for their structural/morphological and fracture mechanical behaviour. The fracture properties were studied following the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. The structural attributes and its consequent effects on the dynamic mechanical properties were characterized by wide angle X-ray diffraction (WAXD), hot-stage polarized light optical microscopy (PLOM) and dynamic mechanical analysis (DMA). The WAXD studies have revealed a decrease in crystallinity of the composites with increase in cenosphere content. PLOM studies reveals a threefold reduction in the diameter of the spherulite in case of composite with 10 wt% of cenosphere compared to that of PP followed by an increase of ~50% in the composite with 20 wt% of cenosphere compared to that of the composite with 10 wt% cenosphere. DMA revealed an enhancement in the energy dissipation ability of the composite with 10 wt% of cenosphere and an increase in the storage modulus up to ~30% in the composites relative to the soft PP phase. The non-essential work of fracture (NEWF: βw _p) as the resistance to stable crack propagation has shown a maximum at 10 wt% of cenosphere followed by a sharp drop at higher cenosphere content indicating a cenosphere-induced ductile-to-brittle transition (DBT). Fractured surface morphology investigations revealed that the failure mode of the composites undergo a systematic transition from matrix-controlled shear deformation to filler-controlled quasi-brittle modes above a cenosphere loading of 10 wt% in the composites reiterating the possibility of filler-induced semiductile-to-DBT transition.     

Synthesis,characteristic, and flammability of modified carbon nanotube/poly(ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate) nanocomposites containing phosphorus and silicon

A novel flame retardant containing phosphorus–silicon, spirocyclic pentaerythritol bisphosphorate disphosphorylchloride/9,10-dihydro-9-oxa-10-phosphaphanthrene-10-oxide/vinyl methyl dimethoxysilane (SPDV), has been used to modify multiwalled carbon nanotubes (MWNTs) and the m-MWNTs (MWNTs-g-SPDV) was obtained by the covalent grafting of SPDV onto the surfaces of MWNTs. And then the according poly(ethylene-co-vinyl acetate) nanocomposites were prepared via melt blending. Transmission electron microscopy (TEM) results showed that a core–shell nanostructure with MWNTs as the hard core and SPDV as the soft shell was formed, and the resultant m-MWNTs can achieve better dispersion than pristine MWNTs in EVM matrix. Cone calorimeter results showed that better flame retardancy was obtained for EVM/m-MWNTs nanocomposites. Mechanical measurements showed that the Young’s modulus increases due to the presence of MWNTs or m-MWNTs. The flammability and mechanical properties of the nanocomposites are strongly dependent on the dispersion state of nanotubes.     

Synthesis and characterization of <Emphasis Type="Italic">n</Emphasis>-ZnO:Al/CoPc/<Emphasis Type="Italic">p</Emphasis>-Si structures

Photosensitive structures of the n-ZnO:Al/CoPc/p-Si type were synthesized for the first time using vacuum sublimation of cobalt phthalocyanine (CoPc) and magnetron sputtering of a ZnO:Al target. The maximum photoresponse is observed when the structure is illuminated from the side of the ZnO layer and amounts to ?400 V/W at T = 300 K. Mechanisms of current transfer and peculiarities of the photosensitivity spectrum are considered. It is suggested that the new photosensitive structures can be used in multiband photoconverters of natural radiation with a broad working spectral range.     

Thermal stability and melt rheology of poly(<Emphasis Type="Italic">p</Emphasis>-dioxanone)

Melt viscosities of poly(p-dioxanone) (PPDO) samples having different molecular weights were studied using a controlled-strain rotational rheometer under a nitrogen atmosphere. First, PPDO’s thermal stability was evaluated by recording changes in its viscosity with time. The result, that samples’ viscosities decreased with time when heated, demonstrated that PPDO is thermally unstable: its degradation activation energy, obtained by using a modified MacCallum equation, was a relatively low 71.8 kJ/mol K. Next, viscoelastic information was acquired through dynamic frequency measurements, which showed a shear thinning behavior among high molecular weight PPDOs, but a Newtonian flow behavior in a low molecular weight polymer (M _w = 18 kDa). Dynamic viscosity values were transferred to steady shear viscosities according to the Cox–Merz rule, and zero shear viscosities were derived according to the Cross model with a shear thinning index of 0.80. Then flow activation energy (48 kJ/mol K) was extrapolated for PPDO melts using an Arrhenius type equation. This activation energy is independent of polymer molecular weight. A linear relationship between zero shear viscosity and molecular weight was obtained using a double-logarithmic plot with a slope of 4.0, which is near the usually observed value of 3.4 for entangled linear polymers. Finally, the rheological behaviors of PPDO polymer blends having bimodal molecular weight distributions were investigated, with the results indicating that the relationship between zero shear viscosity and low molecular weight composition fraction can be described with a Christov model.     

Inference with progressively censored <Emphasis Type="Italic">k</Emphasis>-out-of-<Emphasis Type="Italic">n</Emphasis> system lifetime data

A system with n independent components which works if and only if a least k of its n components work is called a k-out-of-n system. For exponentially distributed component lifetimes, we obtain point and interval estimators for the scale parameter of the component lifetime distribution of a k-out-of-n system when the system failure time is observed only. In particular, we prove that the maximum likelihood estimator (MLE) of the scale parameter based on progressively Type-II censored system lifetimes is unique. Further, we propose a fixed-point iteration procedure to compute the MLE for k-out-of-n systems data. In addition, we illustrate that the Newton–Raphson method does not converge for any initial value. Finally, exact confidence intervals for the scale parameter are constructed based on progressively Type-II censored system lifetimes.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.