Effect of synthetic polymers on polymer–protein interaction

Synthetic polymers are often used for delivery of therapeutic drugs and proteins. We report the binding of milk β-lactoglobulin (β-LG) with poly(ethylene glycol) (PEG), methoxypoly(ethylene glycol) polyamidoamine (mPEG-PAMAM-G-3) and polyamidoamine (PAMAM-G4) nanoparticles in aqueous solution at pH 7.4, using Fourier Transform infrared (FTIR), circular dichroism (CD), fluorescence spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling. Structural analysis showed that polymers bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants K_{PEG-8000-β-LG} = 4.8 (±0.4) × 10⁴ M⁻¹ and K_{mPEG-PAMAM-G3-β-LG} = 5.8 (±0.6) × 10⁵ M⁻¹ and K_{PAMAM-G4-β-LG} = 6.7 (±0.9) × 10⁴ M⁻¹. The number of binding sites were occupied by polymers on protein (n) was 0.3 for PEG-8000, 0.4 for mPEG–PAMAM-G3 and 0.4 for PAMAM-G4. The order of binding is mPEG-PAMAM-G3 > PAMAM-G4 > PEG-8000. Transmission electron microscopy showed significant changes in protein morphology as polymer–protein complexation progressed with major increase in the diameter of the protein aggregate (180%). Furthermore, modeling showed several H-bonding systems between PEG and different amino acids stabilize polymer–β-LG complexes. mPEG-PAMAM-G3 is a stronger protein binder than PAMAM-G4 and PEG-8000.     

Effects of amorphous silica nanoparticles and polymer blend compositions on the structural,thermal and dielectric properties of PEO–PMMA blend based polymer nanocomposites

The polymer nanocomposite (PNC) films consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend matrices dispersed with nanoparticles of amorphous silica (SiO₂) have been prepared by solution-cast method followed by melt-press technique. Effects of SiO₂ concentration (x?=?0, 1, 3 and 5 wt%) and PEO–PMMA blend compositional ratios (PEO:PMMA?=?75:25, 50:50, and 25:75 wt%) on the surface morphology, crystalline phase, polymer-polymer and polymer-nanoparticle interactions, melting phase transition temperature, dielectric permittivity, electrical conductivity, electric modulus and the impedance properties of the PNC films have been investigated. The crystalline phase of the PNC films decreases with the increase of PMMA contents which also vary anomalously with the increase of SiO₂ concentration in the films. The melting phase transition temperature and polymer-nanoparticle interactions significantly change with the variation in the compositional ratio of the blend polymers in the PNC films. It is observed that the effect of SiO₂ on the dielectric and electrical properties of these PNCs vary greatly with change in the compositional ratio of PEO and PMMA in the blends. The dielectric relaxation process of these films confirm that the polymers cooperative chain segmental dynamics becomes significantly slow when merely 1 wt% SiO₂ nanoparticles are dispersed in the polymer blend matrix.     

Influence of B2O3 on viscosity and structure of the CaO–Al2O3-waste electrolyte (WE) based melt

The fluorides contained waste electrolyte (WE) from the electrolytic aluminum industry can be used as a substitution of fluorite (CaF₂) in the newly designed mold flux. In this study, the influence of B₂O₃ on viscosity and structure of CaO–Al₂O₃-WE based melt was investigated. Results show that the viscosity of mold flux melt decreases with both increasing temperature and B₂O₃ content. The apparent activation energy (E_a) also reduces from 78.96 ± 1.75 to 55.26 ± 2.79 kJ/mol with the addition of B₂O₃ from 0 to 7 wt%. The analyses of fourier transform infrared (FTIR) and Raman spectroscopies suggest that the lower symmetry of the original aluminate and silicate structure due to the insertion of [BO₄]-tetrahedral and [BO₃]-triangular, and the formation of more non-bridging oxygen (O⁻) and 2D structural units in the network with the addition of B₂O₃, deceases the viscosity and E_a of the CaO–Al₂O₃-WE Based Melt.     

Influence of vibrations on interface delamination in metal–polymer composites

The main objective of this work was the study of vibration effects on the viscoelastic coating protecting the steel layer in a metal–polymer composite, with simulated conditions of the transportation of food containers. Mechanical resonance tests in metal–polymer [electrolytic chromium-coated steel–poly(ethylene terephthalate) (PET)] sheets were performed to generate vibration conditions to induce structural modifications in the viscoelastic layer covering the surface of the plates. Consequently, schematic representations of the areas affected by these modifications were made. The modified structures were later analyzed by electron microscopy to detect and evaluate alterations in the morphology of the material. In addition, vibrational Raman spectroscopy analyses were performed to assess the chemical and structural changes on the protective PET at the metal–polymer interface level. The results of this study are expected to provide basic information on the mechanisms and nature of the delamination processes taking place in metal–polymer laminates employed in food-container applications. These damages have previously been detected in some food containers made of PET materials. The study of these damages can lead to the improvement of current composites or the development of higher quality materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of hygrothermal and ambient humidity conditioning on shear strength of metal–GFRP single lap joints co-cured in and out of water

Installing and repairing of oil and gas infrastructure is required to be conducted out of water (OW) and in water (IW). In service, this infrastructure is subjected to various environmental ageing which may affect its mechanical performance. In this study the shear strength of metal–glass epoxy prepreg composites was investigated using single lap joint (SLJ) testing. For this, three different surface preparation methods (grit blasting, wire brushing and needle gunning) and two different manufacturing methods (OW and IW) were employed. Results showed that the specimens prepared by grit blasting had superior shear strength followed by these by needle gunning and wire brushed for both OW and IW methods. Manufactured specimens were also subjected to hygrothermal conditioning (WC) and ambient humidity conditioning (HC) to assess the durability of the produced SLJ specimens. The WC specimens absorbed more moisture than the HC specimens and the shear strength of the WC specimens were found to have deteriorated more than the HC specimens. For the conditioned SLJ specimens, the lower loss of shear strength was found with specimens manufactured IW when compared to specimens manufactured OW for grit blasted and needle gunned specimens and an opposite trend was seen for wire brushed specimens. However, the loss of shear strength was found to be varied with the moisture uptake for individual surface preparation technique and the variation was considered to be due to a combination of many factors other than the type of adhesive used such as metal surface profile, failure mode, rust formation and presence of black coloured metallic remnants.     

Is the structural relaxation of glasses controlled by equilibrium shear viscosity?

Knowledge of relaxation processes is fundamental in glass science and technology because relaxation is intrinsically related to vitrification, tempering as well as to annealing and several applications of glasses. However, there are conflicting reports—summarized here for different glasses—on whether the structural relaxation time of glass can be calculated using the Maxwell equation, which relates relaxation time with shear viscosity and shear modulus. Hence, this study aimed to verify whether these two relaxation times are comparable. The structural relaxation kinetics of a lead metasilicate glass were studied by measuring the refractive index variation over time at temperatures between 5 and 25 K below the fictive temperature, which was initially set 5 K below the glass-transition temperature. Equilibrium shear viscosity was measured above and below the glass-transition range, expanding the current knowledge by one order of magnitude. The Kohlrausch equation described very well the experimental structural relaxation kinetics throughout the investigated temperature range and the Kohlrausch exponent increased with temperature, in agreement with studies on other glasses. The experimental average structural relaxation times were much longer than the values computed from isostructural viscosity, as expected. Still, they were less than one order of magnitude higher than the average relaxation time computed through the Maxwell equation, which relies on equilibrium shear viscosity. Thus, these results demonstrate that the structural relaxation process is not controlled by isostructural viscosity and that equilibrium shear viscosity only provides a lower boundary for structural relaxation kinetics.     

Effect of polymer–nanoparticle interactions on the glass transition dynamics and the conductivity mechanism in polyurethane titanium dioxide nanocomposites

We report on the glass transition dynamics and the conductivity properties of a nanodielectric system composed of pre-synthesized TiO₂ nanoparticles embedded in thermoplastic polyurethane. Increase of TiO₂ loading results in enhanced segmental mobility of the composites and less steep temperature dependence, i.e., lower fragility index. The decrease in the fragility index and glass transition temperature is discussed based on the FTIR results. We observe different behavior of conductivity for temperatures above and below the glass transition temperature. At high temperatures the composites exhibit conductivity values more than 2 orders of magnitude higher than those in the pristine matrix. At the same time, at sub-T_g temperatures composites are characterized by superior electrical insulation properties compared to pristine matrix material. Such drastic temperature dependence of the conductivity/insulating ability of the flexible and light-weight, low-T_g composite material can be utilized in various applications including sensing and temperature switching materials.     

Effects of hard-segment compositions on properties of polyurethane–nitrolignin films

Segmented polyurethane (PU) films from castor-oil-based PU prepolymer with different hard-segment compositions and nitrolignin (NL) were synthesized. Diisocyanates (DIs), such as 2,4-tolylene DI (TDI) and 4,4′-diphenylmethane DI (MDI), 1,4-butanediol (BDO) as a chain extender, and trimethanol propane (TMP) as a crosslinker were used to obtain PU films containing NL (UL) which were named as UL–TB for TDI and BDO, UL–TT for TDI and TMP, UL–MB for MDI and BDO, and UL–MT for MDI and TMP, respectively. The mechanical properties and thermal stability of the films were characterized by a tensile test and thermogravimetric analysis, respectively. The MDI-based UL films exhibited a higher tensile strength (σ_b) and thermal stability than TDI-based UL. However, the recoverability of the TDI-based UL films was better than that of others. The UL films with TMP (UL–TT and UL–MT) had higher σ_b and lower breaking elongation (ϵ_b) than the UL films with BDO (UL–TB and UL–MB), caused by enhancement in the crosslinking network of hard segments and microphase separation between soft and hard segments. The values of σ_b and ϵ_b of the UL films that contained NL were much higher than those of the PU films, which indicates that the introduction of NL increased the interaction between hard segments by crosslinking. The hydrogen bonding in the UL films was studied by infrared spectroscopy, which indicated that MDI favored the formation of hydrogen bonds, especially in the ordered domain. Differential scanning calorimetry, dynamic mechanical analysis, and wide-angle X-ray diffraction indicated that the UL films were compatible as a whole, but microphase separation existed between soft and hard segments and significantly affected the mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3251–3259, 2001     

Effect of Li2O on melt crystallization of CaO–SiO2–CaF2 based glasses

This paper presents the effects of Li₂O on the kinetics and structural aspects of the Cuspidine (Ca₄Si₂F₂O₇) crystallization behavior of CaO–SiO₂–CaF₂ glass (basicity 1.7). In order to elucidate the crystallization characteristics during differential scanning calorimetry (DSC) measurements, the kinetic parameters have been determined using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The crystallization rate constant and negative activation energy thus calculated indicated that the limiting step of crystallization was nucleation. Also, Raman spectroscopy and Solid-state MAS NMR spectroscopy analyses indicated that lithium could interact with fluorine, thereby disturbing the interaction between calcium and fluorine. This retards Cuspidine nucleation at the initial stage of melt crystallization. These findings on CaO–SiO₂–CaF₂-based glass lubricants can be used to optimize essential properties such as viscosity and crystallization temperature during continuous casting of steels.     

Effects of aggregate size on alkali–silica-reaction induced expansion

The macroscopic effects of ASR are linked to the damage state at the microstructure level. In this paper we used a combination of experiments and modelling to study the effect of aggregate size on the manifestation of ASR. There are two main ways in which the size of the aggregates can affect damage evolution: the propagation of cracks in aggregates of different sizes and the interactions between expanding and non-expanding aggregates in a densely packed microstructure. To assess these effects, concretes were cast with the same PSD but each with a different size class of reactive aggregates. Numerical simulations were used to model the mechanical interactions in single aggregates and in complete microstructures at the mesoscopic level. From the simulations a mechanism is proposed to explain the experimental observations. This suggests that: the expansion rate of ASR affected concrete depends on the fracture behaviour of individual aggregates in the early stage, and on the fracture behaviour of the paste in the later stages.     

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.     

The Effects of Nectar–Nicotine on Colony Fitness of Caged Honeybees

Nectar of many bee flowers contains secondary compounds, which are considered toxic for honeybees on repeated exposure. Although many anecdotal reports indicate the toxicity of secondary compounds to bees, only a few studies have tested the extent of toxicity at different honeybee ages, especially at the larval stages. Honeybees encounter nicotine at trace concentrations (between 0.1 and 5 ppm) in floral nectar of a few Nicotiana spp. and in Tilia cordata. Adult honeybee workers tolerate these nicotine concentrations. In controlled nonchoice feeding experiments with caged bees, we investigated the effect of nicotine on hatching success and larval and forager survival. Naturally occurring concentrations of nectar–nicotine did not affect hatching success of larvae or their survival, but the latter was negatively affected by higher concentrations of nicotine (50 ppm). Concentrations of nicotine in fresh honey samples from the hives were 90% lower than the concentrations in the offered experimental sucrose solutions. Our results indicate that honeybees can cope with naturally occurring concentrations of nicotine, without notable mortality, even when consumed in large quantities for more than 3 weeks.     

Interpenetrating polymer networks based on uralkyd–butylmethacrylate

Two-component semi- and full-interpenetrating polymer networks (IPNs) of hydrogenated castor oil based uralkyd resin (UA) and poly(butylmethacrylate) (PBMA) were synthesized by the sequential technique. The elastomers obtained were characterized with respect to their mechanical properties such as tensile strength, elongation at break and hardness (Shore A). The apparent densities of these samples were determined and compared. Glass transition studies were carried out using differential scanning calorimetry. The thermal characterization of the elastomers was undertaken with the aid of thermogravimetric analysis. Phase morphology was studied by scanning electron microscopy. The effect of the variations of UA–PBMA on the above-mentioned properties was examined. The elongation percentage at break showed higher values in the case of all the semi-IPNs as compared to the full-IPNs.     

Effects of nucleation agents on the preparation of transparent glass–ceramics

Formation of transparent glass–ceramic in the system MgO–SiO₂–Al₂O₃–K₂O–B₂O₃–F with and without addition of LiF and NaF has been investigated. Crystallization of glass-sample was conducted by controlled thermal heat-treatment, at determined nucleation and crystallization temperatures. In this regard, the effects of addition of LiF and NaF were investigated on the crystallization behavior and transparency of the samples.Low transmission (less than 80% at 600 nm) was observed in the basic composition (K).The addition of NaF and LiF caused more intense phase separation in the system.The results indicated that the glass–ceramic can remain transparent if fine grains with nano size are precipitated but will turn into opaque when large grains appear, because of the difference in the refractive index between glass and precipitated crystals.     

Effects of saccharin on the electrodeposition of Ni–Co nanocrystalline coatings

Nickel–Co nanocrystalline coatings were electrodeposited onto a carbon steel substrate with and without saccharin addition. In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished as two effective parameters causing nanocrystalline electrodeposits. In the latter case, the growth active sites can be blocked easily at low current densities. By increasing the current density, a lower degree of adsorption was associated by a significant increase in surface diffusion of adions resulting in grain growth. Although, the nucleation rate is expected to increase with current density, it seems that the Ni–Co grain size is not reduced by the nucleation rate. Adsorption of saccharin molecules and/or decomposed sulfide species occurred in the saccharin contained bath, resulting in slow surface diffusion of adions. Therefore, finer grains were obtained which produced a smooth morphology instead of the pyramidal forms obtained in the absence of saccharin.     

Influence of particle size distributions on yield stress and viscosity of cement–fly ash pastes

The rheological properties of blended cement-based materials depend strongly on mixture proportions and the characteristics of the components. In this study, design of experiments is used to investigate the influence of three variables (cement particle size distribution (PSD), fly ash PSD, and ratio of fly ash to cement) at each of four levels on the yield stress and viscosity of blended pastes. Both rheological parameters are seen to vary over several orders of magnitude for the evaluated design space. Physical characteristics of the powders, such as cement and total particle densities and total particle surface area, are computed for each mixture. A percolation-type relationship is observed between yield stress and cement particle (number) density. While neither apparent nor plastic viscosities were particularly well described by the commonly employed Kreiger–Dougherty equation, plastic viscosities were found to be linear functions of either total (cement + fly ash) particle surface area or total particle density.     

Plasma–melt processing of carbon-containing raw materials

The experimental and theoretical studies of the gasification of solid organic compounds by a melt technology were carried out for the two types of carbon-containing materials: slime and tar. The experimental works and the simulation showed that this gasification method can be used for the effective utilization of oilrefining and petrochemical-processing wastes with the simultaneous production of high-purity synthesis gas.     

Effects of Mo addition on tribological performance of plasma-sprayed Ti–Si–C coatings

Ti–Si–C–Mo composite coatings were fabricated by plasma spraying using Ti, Si, graphite and Mo powders. The effect of Mo on microstructure and tribological performance of the Ti–Si–C coatings were investigated. The results showed that the Ti–Si–C coating consisted of TiC, Ti₃SiC₂, Ti₅Si₃, and residual graphite. The Ti–Si–C–Mo coatings consisted of TiC, Ti₃SiC₂, Ti₅Si₃, residual graphite, Mo and Mo₅Si₃ phases. With increasing Mo contents, the fractions of Mo and Mo₅Si₃ phases increased, and the fractions of Ti₃SiC₂ and Ti₅Si₃ phases decreased. All the coatings existed a typical lamellar structure. The addition of Mo enhanced the hardness and fracture toughness of Ti–Si–C coating by 16% and 52%, respectively. The coating porosity decreased by 57.6%. The wear resistance of the Ti–Si–C coating was also improved and the mass loss decreased by 83%. The wear mechanism of the Ti–Si–C–Mo coatings was the combination of abrasive wear, adhesive wear, and tribo-oxidation wear.