Anodization of n and p-GaAs in ethylene glycol–water–tartaric acid mixture

This paper describes the pulsed constant current anodization of n+ and p+-GaAs in ethylene glycol–water–tartaric acid (AGW) mixture, up to 17mAcm–2. A 0.26m thick film is obtained for a final voltage of 135V at 4.3mAcm–2 pulsed current density. Cyclic voltammetry showed that the initial growth of a monolayer anodic oxide can be described by a charge transfer with uncompensated cell resistance model. The relationship between peak current, peak voltage and scan rate has been verified for this process, based on the above model.     

Inhibiting effect of cerium ions on corrosion of 3003 aluminum alloy in ethylene glycol–water solutions

In this study, the inhibiting effect of cerium ions (Ce³⁺) on corrosion of 3003 aluminum alloy (AA3003) in ethylene glycol–water solutions was investigated using a rotating cylinder electrode, simulating the hydrodynamic condition of the automotive cooling system. Electrochemical measurements and surface characterization were conducted to study the inhibiting mechanism of Ce³⁺ on the Al alloy corrosion. It is found that Ce³⁺ serves as a cathodic inhibitor, and inhibits effectively corrosion of AA3003 in the flowing ethylene glycol–water solutions. The inhibiting effect of Ce³⁺ is resulted from the formation and deposit of Ce oxide and/or Ce hydroxide on the electrode surface. With the immersion time, the Ce deposit layer increases its thickness to cover the second phase particles, eliminating the galvanic coupling effect between the second phase particles and Al alloy substrate.     

Molecular weight effect on theta-gel formation in poly(vinyl alcohol)–poly(ethylene glycol) mixtures

Injectable hydrogel formulations that undergo in situ gelation at body temperature are promising for minimally invasive tissue repair. This work focuses on the investigation of injectable poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) mixtures. The injectable PVA–PEG aqueous solutions form a hydrogel as temperature is reduced to near body temperature, while filling a defect in the injection site. Gamma sterilization of these solutions compromises injectability presumably due to crosslinking of PVA. We hypothesized that by modifying the PEG molecular weight and its concentration, injectability of radiation sterilized PVA–PEG hydrogels can be optimized without compromising the mechanical properties of the resulting gel. The use of a bimodal mixture of higher and lower molecular weight PEG (600 and 200 g/mol) resulted in lower PVA/PEG solution viscosity, better injectability, and higher gel mechanical strength. The PVA/bimodal-PEG had a lower viscosity at 2733 ± 149 cP versus a viscosity of 5560 ± 278 cP for PVA/unimodal-PEG (400 g/mol). The gel formed with the bimodal PEG mixture had higher creep resistance (61% total creep strain under 0.5 MPa) than that formed with unimodal PEG (84%). These hydrogel formulations are promising candidates for minimally invasive tissue repair. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Photocrosslinking of styrene–isoprene–styrene; effect of benzoin and ethylene glycol dimethacrylate on physical properties

Crosslinking reaction of polymer by ultraviolet (UV) irradiation has been important in industries. In this work, photocrosslinking of styrene–isoprene–styrene (SIS) triblock copolymer in the presence of benzoin photoinitiator and a dimethacrylate monomer as crosslinking agent was investigated. Curing of samples was initiated under UV irradiation. Benzoin was used as photoinitiator because it contains chromophore group that could absorb UV irradiation. Ethylene glycol dimethacrylate (EGDMA) was used as crosslinking agent, since it has alkene functional groups that could react with the alkene group of SIS. ATR-FTIR spectra of samples show that absorption band of double bond at 1500–1600?cm^?1 decreases after UV exposure. Increasing the concentration of benzoin (0.1–1?phr) and EGDMA (1–10?phr) leads to an increase in gel content and hardness, while swelling ratio decreases. After 5?min heating at 150?°C, about 20%wt of the unirradiated compound became insoluble, because heating of compound at 150?°C causes crosslinking reaction without any irradiation.     

Aggregation and adsorption behavior of cobalt-based metallosurfactant in water–ethylene glycol media forming worm-like micelles

The cobalt based metallosurfactant cis-chlorobis(ethylenediamine)hexadecylaminecobalt(III) chloride (CHCC) has been prepared and well characterized by utilizing elemental analysis, NMR (¹H, ¹³C), FT-IR and UV–Vis spectroscopy. The CHCC metallosurfactant shows thermal stability up to 168°C. The micellization behavior of the synthesized CHCC metallosurfactant has been investigated systematically by the tensiometric, conductometric, and fluorescence techniques. The critical micelle concentration (cmc) values of CHCC have been determined in various water–ethylene glycol mixtures ranging from 0 to 100 weight % of ethylene glycol at 293.15, 298.15, 303.15, and 308.15 K. The physicochemical parameters namely counterion binding constant, surface pressure, surface excess, surface area covered per CHCC metallosurfactant molecule, free energy minimum, standard free energies of micellization and adsorption, standard enthalpy and entropy of micellization, and Gibb's free energy of transfer have been calculated. The hydrodynamic diameters and zeta potentials of the CHCC metallomicelles have been measured by dynamic light scattering method. Transmission electron microscopy was employed to confirm the presence of worm-like micelles.     

Characterization of passivity and pitting corrosion of 3003 aluminum alloy in ethylene glycol–water solutions

In this work, the passivity and pitting corrosion behavior of 3003 aluminum (Al) alloy in ethylene glycol–water solutions was investigated using various electrochemical measurements, Mott–Schottky analysis and surface analysis techniques. Results demonstrate that the passive film formed on Al alloy contains both Al oxide and Al alcohol, showing an n-type semiconductor in nature. There is an enhanced corrosion resistance of the Al-alcohol film, which is resistant to adsorption of chloride ions. The pitting corrosion of 3003 Al alloy occurs in the solutions containing a low concentration of ethylene glycol only, where the formed film is dominated by Al oxide. Chloride ions attack and replace the oxygen vacancies in the film, resulting in a local detachment of the film from the Al alloy. A galvanic effect exists between Al alloy substrate and the adjacent second phase particles. Pits form when Al alloy substrate is dissolved away and the second phase particles drop off from the substrate.     

Mixed micelles from methoxy poly(ethylene glycol)–polylactide and methoxy poly(ethylene glycol)–poly(sebacic anhydride) copolymers as drug carriers

mPEG–PLLA (poly l-lactic acid) is synthesized by ring-opening polymerization of lactide and conjugation with mPEG. Sebacic acid is modified with acetic anhydride and condensed with mPEG to form mPEG–PSA (poly sebacic anhydride). The micelles formed by mPEG–PLLA are characterized by slow degradation and low drug encapsulation efficiency; on the contrary, mPEG–PSA micelles are characterized by rapid degradation but high encapsulation efficiency. They can merge into spherical micelles (Φ = 140 nm) by self-assembly in water. The mixed micelles can successfully encapsulate a typical hydrophobic drug (curcumin), and significantly improve its solubility. Experimental results show that the mixed micelles have the features of high encapsulation efficiency and slow degradation.     

Biodegradable nanoparticles of methoxy poly(ethylene glycol)-b-poly( d, l-lactide)/methoxy poly(ethylene glycol)- b-poly(ϵ-caprolactone) blends for drug delivery

The effects of blend weight ratio and polyester block length of methoxy poly(ethylene glycol)-b-poly( d, l-lactide) (MPEG- b-PDLL)/methoxy poly(ethylene glycol)- b-poly(ϵ-caprolactone) (MPEG- b-PCL) blends on nanoparticle characteristics and drug release behaviors were evaluated. The blend nanoparticles were prepared by nanoprecipitation method for controlled release of a poorly water-soluble model drug, indomethacin. The drug-loaded nanoparticles were nearly spherical in shape. The particle size and drug loading efficiency slightly decreased with increasing MPEG- b-PCL blend weight ratio. Two distinct thermal decomposition steps from thermogravimetric analysis suggested different blend weight ratios. Thermal transition changes from differential scanning calorimetry revealed miscible blending between MPEG- b-PDLL and MPEG- b-PCL in an amorphous phase. An in vitro drug release study demonstrated that the drug release behaviors depended upon the PDLL block length and the blend weight ratios but not on PCL block length.     

Magnetite nanoparticles stabilized with polymeric bilayer of poly(ethylene glycol) methyl ether-poly(?-caprolactone) copolymers

In this work, we report a synthetic method of water dispersible magnetite nanoparticles having oleic acid and poly(ethylene glycol) methyl ether-poly(?-caprolactone) (mPEG-PCL) amphiphilic block copolymer as polymeric stabilizers. The particles were prepared by coprecipitation of Fe(II) and Fe(III) in NH₄OH and had bilayer surface with hydrophobic inner layer and hydrophilic corona. mPEG-PCL copolymer was synthesized by a ring-opening polymerization of ?-caprolactone using mPEG as a macroinitiator in the presence of stannous octoate catalyst. FTIR and thermogravimetric analysis (TGA) indicated the presence of the copolymer on the particle surface. Roles of reaction parameters, such as stabilizer concentrations and time of ultrasonicating treatment, on percent of magnetite in the complex and its magnetic properties were investigated. Transmission electron microscopy (TEM) showed the average particle size about 9.0 ± 1.1 nm in diameter. Vibrating sample magnetometry (VSM) measurement indicated that the magnetite nanoparticles were superparamagnetic at room temperature. Approximately 6.8 ± 0.5% of indomethacin model drug (68 μg/mg of magnetite) was effectively entrapped on the particles.     

Measurement and correlation of vapor–liquid equilibra for cyclohexane + ethylene glycol monoisopropyl ether and cyclohexane + ethylene glycol monoisobutyl ether systems

Ethylene glycol monoisopropyl ether (iC₃E₁) and ethylene glycol monoisobutyl ether (iC₄E₁) are nonionic surfactants which have been attracting considerable attention due to inter and intra-molecular association, related to the presence of O and OH in the same molecule. Binary isothermal vapor + liquid equilibrium data were measured for cyclohexane + ethylene glycol monoisopropyl ether and cyclohexane + ethylene glycol monoisobutyl ether systems at four different temperatures ranging from 303.15 K to 333.15 K at 10 K intervals. A static apparatus was used in this study. Two systems show positive deviation from Raoult's law and no azeotrope. The experimental data were correlated well with Peng–Robinson–Stryjek–Vera equation of state using Wong–Sandler mixing rule.     

Effects of liquid–liquid phase separation on crystallization of poly(ethylene glycol) in blends with isotactic poly(methyl methacrylate)

To analyze the interplay between crystallization and liquid–liquid phase separation (LLPS), isothermal crystallization behavior of poly(ethylene glycol) (PEG) in blends with isotactic poly(methyl methacrylate) (i-PMMA) was investigated by differential scanning calorimetry (DSC). The blend system had an upper critical solution temperature (UCST) type phase diagram. When the crystallization occurred simultaneously with LLPS, the overall crystallization rate was enhanced at high crystallization temperatures T_c, relatively compared with that of neat PEG. This behavior was interpreted by the combination of the effects of spinodal quench depth ?T_s and usual supercooling degree ?T_c, according to the theory of Mitra and Muthukumar, namely, the crystallization rate is enhanced by the concentration fluctuation-assisted nucleation at high T_c. In the crystallization after LLPS proceeded, on the other hand, the overall crystallization rate was slow and less dependent on the blend composition. In addition, it was revealed by small-angle X-ray scattering measurements that amorphous i-PMMA was excluded from the interlamellar region of PEG crystals in SQ as well as WQ.     

Role of Sn on the adhesion in Cu–Sn alloy-coated steel–rubber interface

Cu–Sn coatings with varying Sn content were deposited on steel substrate by immersion route and the effect of variation of Sn content and the substrate roughness on the interfacial adhesion strength of Cu–Sn-coated steel substrates vulcanized with styrene butadiene rubber were investigated. The surface roughness of the coatings did not vary compared to pristine steel substrate with change in Sn weight% in the coatings. The coated surfaces exhibited bare spots or deep trough as micro-discontinuities in the coatings, where formation of Fe₂O₃ was evident from SEM-EDS, AES, and XPS analysis. Microstructural study of the coating cross-section and coating-substrate interface by transmission electron microscopy of cross-sectioned samples revealed inadequate penetration of coating inside these troughs. Peel test carried out on the Cu–Sn-coated steel–rubber joints showed mixed mode i.e. adhesive and cohesive mode of interfacial fracture irrespective of the coating composition. The peel test further indicated higher interfacial adhesion strength for Cu–Sn-coated samples than pure Cu-coated samples, with an optimum adhesion strength for the coatings containing 3–4?wt.% Sn.     

Electrochemical noise analysis on the crevice corrosion behavior of Ni–Cr–Mo–V high strength steel using recurrence plots

This article makes a study of electrochemical noise analysis on the crevice corrosion behavior of Ni–Cr–Mo–V high strength steel using recurrence plots. The crevice corrosion behavior of Ni–Cr–Mo–V high strength steel was investigated by the electrochemical noise (EN) technique and SEM observation. The experimental results reveal that the crevice corrosion could be distinguished by three stages including induction stage, transformation stage, and stable stage. While increasing the growth probability of metastable corrosion, the presence of crevice decreases the initiation rate of metastable corrosion. In the case of crevice, the metastable corrosion is easy to develop into stable one.     

Studies on thermodynamic properties of pure poly(ethylene glycol)-400 in the temperature range 299–363 K using volume expansivities

Dilatometric studies have been performed on the pure poly(ethylene glycol) of average molecular mass 400 g.mol^?1(PEG-400). From these studies, molar volumes and volume expansion coefficients (α) of this sample have been estimated at different temperatures. Using the data, a number of thermodynamic, thermo-acoustic and anharmonic parameters of the sample have been evaluated. All these parameters have been discussed to throw light on the internal structure, molecular order, anharmonicity and intermolecular interactions.     

Effect of brookite phase on the anatase–rutile transition in titania nanoparticles

Nanosized TiO₂ powders were prepared from the precipitation in the TiCl₄ precursor under various pH values. The prepared titania existed in the form of nanocrystalline anatase with some brookite, which was evidenced by X-ray diffraction analysis and Raman spectroscopy. The average crystallite sizes of the TiO₂ particles heat treated at 450 °C for 2 h are in the range of 7–9 nm. The lattice constant c of anatase increased with increasing the synthesized pH value, whereas the volume fraction of the brookite phase increased with decreasing the synthesized pH value. The beginning and ending temperatures for the anatase–rutile transformation were found to decrease with increasing the volume fraction of the brookite phase. The brookite phase in the powder is responsible for enhancing the anatase–rutile transition.     

Pulse electrodeposition of titanium on carbon steel in the LiF–NaF–KF eutectic melt

Electrodeposition of titanium was carried out in the K₃TiF₆–LiF–NaF–KF melt using both direct (DC) and unipolar pulse current (PC) techniques. Dense and smooth titanium coatings were obtained by PC plating at 750 °C whereas DC plating led to rough and dendritic deposits. The best results were obtained using a 100C cm^–2 pulse charge and a cathodic current density of 50 and 75mA cm^–2. The cathodic current efficiency was in the range 60–65%. The titanium deposits obtained under such conditions behaved similarly to CP-titanium in NaCl and HNO₃ solutions at room temperature.     

Optimum design of co-cured steel–composite tubular single lap joints under axial load

In this paper, an optimum design method for co-cured steel-composite tubular single lap joints under axial load is proposed based on a failure model which incorporates the nonlinear mechanical behavior of the steel adherend and the failure mode of joints such as composite adherend failure and steel adherend failure. The design parameters considered were the test temperature, the stacking sequence of the composite adherends, the thickness ratio of the steel adherend to the composite adherend, and the existence of scarf in the steel adherend. Stress analysis of the cocured steel-composite tubular single lap joints was performed considering the nonlinear mechanical behavior of the steel adherend, and the fabrication residual thermal stress and thermal degradation of the composite adherend. The method developed may be employed in the joining of hybrid composite structures such as golf clubs and automotive composite propeller shafts in which a carbon/epoxy shaft has normally been bonded to a metal shaft with epoxy adhesives.     

Synthesis of amphiphilic polycyclooctene-graft–poly(ethylene glycol) copolymers by ring-opening metathesis polymerization

In this paper, a novel monomer of 4-methyl-3-(carbamate)–carbanilic acid-4-cyclooctene ester (MCCCE) was synthesized and characterized by FTIR, NMR and ESI-MS. Polycyclooctene-graft-blocked isocyanate copolymers were prepared by the copolymerization of MCCCE and cyclooctene via ring-opening metathesis polymerization (ROMP). Amphiphilic polycyclooctene-graft–PEG copolymers were prepared by melt mixing the polycyclooctene-graft-blocked isocyanate copolymers with poly(ethylene glycol) (PEG) at 200 °C. The blocked isocyanate group on MCCCE can be dissociated to produce free isocyanate group, which will react with the end hydroxyl groups on PEG molecules. The effects of monomer-to-catalyst, monomer-to-chain transfer agent ratios on molecular weight of the copolymer were detailedly studied. The water contact angle of polycyclooctene-graft–PEG copolymer is much smaller than that of polycyclooctene.