Engineered Nanoparticles as Potential Food Contaminants and Their Toxicity to Caco‐2 Cells

Engineered nanoparticles (ENPs), such as metallic or metallic oxide nanoparticles (NPs), have gained much attention in recent years. Increasing use of ENPs in various areas may lead to the release of ENPs into the environment and cause the contamination of agricultural and food products by ENPs. In this study, we selected two important ENPs (zinc oxide [ZnO] and silver [Ag] NPs) as potential food contaminants and investigated their toxicity via an in vitro model using Caco‐2 cells. The physical properties of ENPs and their effects on Caco‐2 cells were characterized by electron microscopy and energy dispersive X‐ray spectroscopic (EDS) techniques. Results demonstrate that a significant inhibition of cell viability was observed after a 24‐h of exposure of Caco‐2 cells to 3‐, 6‐, and 12‐mM ZnO NPs or 0.5‐, 1.5‐, and 3‐mM Ag NPs. The noticeable changes of cells include the alteration in cell shape, abnormal nuclear structure, membrane blebbing, and cytoplasmic deterioration. The toxicity of ZnO NPs, but not that of Ag NPs after exposure to simulated gastric fluid, significantly decreased. Scanning transmission electron microscopy shows that ZnO and Ag NPs penetrated the membrane of Caco‐2 cells. EDS results also confirm the presence of NPs in the cytoplasm of the cells. This study demonstrates that ZnO and Ag NPs have cytotoxic effects and can inhibit the growth of Caco‐2 cells.     

Optimum analytical approach to nonlinear circuit analysis

In this article, an analytical approach, for optimum nonlinear circuit analysis is described. At a given input frequency, the method consists in determining, for each nonlinear component of the circuit, a closed volume including all the allowed powers at its terminal ports. The boundary of this volume, called “characteristic surface,” allows extremum powers of nonlinear devices to be predicted and then optimum performance of the circuit to be deduced. Applied to various microwave transistor circuits, this procedure has shown good agreement between computed and measured or previous published results. © 1996 John Wiley & Sons, Inc.     

Polypropylene/date stone flour composites: Effects of filler contents and EBAGMA compatibilizer on morphology,thermal, and mechanical properties

This work aims to study the effects of date stone flour (DSF) on morphology, thermal, and mechanical properties of polypropylene (PP) composites in the absence and presence of ethylene‐butyl acrylate‐glycidyl methacrylate (EBAGMA) used as the compatibilizer. DSF was added to the PP matrix at loading rates of 10, 20, 30, and 40 wt %, while the amount of compatibilizer was fixed to the half of the filler content. The study showed through scanning electron microscopy analysis that EBAGMA compatibilizer improved the dispersion and the wettability of DSF in the PP matrix. Thermogravimetric analysis (TGA) indicated a slight decrease in the decomposition temperature at onset (T_onset) for all composite materials compared to PP matrix, whereas the thermal degradation rate was slower. Differential scanning calorimetry (DSC) data revealed that the melting temperature of PP in the composite materials remained almost unchanged. The nucleating effect of DSF was however reduced by the compatibilizer. Furthermore, the incorporation of DSF resulted in the increase of stiffness of the PP composites accompanied by a significant decrease in both the stress and strain at break. The addition of EBAGMA to PP/DSF composites improved significantly the ductility due to the elastomeric effect of EBAGMA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Newly designed polyacrylamide/dextran gels for electrophoresis protein separation: synthesis and characterization

Newly designed gels for electrophoresis protein separation were synthesized from acrylamide, N,N′‐methylenebis (acrylamide) and dextran mixtures. Radical polymerization was initiated by ammonium persulfate and N,N,N′,N′‐tetramethylethylenediamine. The time dependence of absorbance during polymerization was monitored using UV‐visible spectroscopy. The exothermic polymerization process exhibited a sharp rise of temperature reminiscent of the Trommsdorff effect. The swelling kinetics of the synthesized gels was examined in deionized water and buffer solutions. One of the challenges was to find an alternative to commercial products, sold as mixtures with no detailed chemical contents, commonly used in sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS‐PAGE) for protein separation. For this reason, a systematic comparison was made of the properties of one of the most commonly used commercial gels, Duracryl^? from Genomics Solution Inc., and those of the synthesized polyacrylamide/dextran gels. Copyright © 2011 Society of Chemical Industry     

Effects of nematic coupling on the phase behaviour of nematogen mixtures

The phase behaviour of binary nematogen mixtures of side‐chain liquid crystal crosslinked polymers and low molecular weight liquid crystals is investigated with particular emphasis on the effects of nematic coupling. The cross nematic quadrupole parameter ν₁₂ is assumed to be proportional to the geometric average of ν₁₁ and ν₂₂ characteristic of single nematogens. In the weak coupling limit, the proportionality constant is lower than 1, and the phase diagram exhibits a reduced miscibility of the nematogens. In the case of strong coupling, the proportionality constant exceeds 1 resulting in higher miscibility. This is characterized by a nematic order that extends to temperatures above the upper nematic–isotropic transition temperature. A wide region of miscibility emerges showing a single nematic phase. Nematogens having similar nematic–isotropic transition temperatures exhibit different phase properties from systems with widely separated transition temperatures. Effects of the polymer volume fraction at crosslinking, rubber elasticity parameters of the network, and the Flory–Huggins interaction parameter on the equilibrium phase diagram of these systems are discussed. © 2001 Society of Chemical Industry     

Phase Behavior of Poly(butyl acrylate) Networks in Nematic Liquid Crystal Solvents

Summary: This paper reports the phase behavior of photochemically crosslinked poly(butyl acrylate) networks in nematic liquid crystal (LC) solvents. The swelling properties are studied as a function of temperature for two low molecular weight nematic LCs, 4‐cyano‐4′‐pentylbiphenyl (5CB) and the eutectic mixture of cyanoparaphenylenes (E7). Chemically crosslinked polymer networks were formed by the UV radiation of initial solutions of the reactive monomer, butyl acrylate, a crosslinker (hexanediol diacrylate), and a photoinitiator. To obtain different network densities, the ratio of butyl acrylate to hexanediol diacrylate was varied prior to polymerization/crosslinking reactions. Immersion in an excess of the LC solvent allowed for the measurement of size increase by polarized optical microscopy in terms of temperature. Length, width, and diagonal ratios were calculated considering swollen to dry network states of the samples. In general, swelling leads to an increase in the network size by increasing the temperature with a significant dependence on the degree of crosslinking. A large shift in the swelling ratio was found in the vicinity of the nematic to isotropic transition temperatures of the LCs.

     

Static and Dynamic Mechanical Behavior of Electron Beam‐Cured Monomer and Monomer/Liquid Crystal Systems

Summary: This paper discusses static and dynamic mechanical properties of electron beam‐cured mixtures made of the nematic liquid crystal (LC) E7 and either tripropyleneglycol diacrylate (TPGDA) or propoxylated glycerol triacrylate (GPTA) as monomers differing essentially by their functionality. Dilution of the initial mixture with LC leads to a significant weakening of the film mechanical strength. Strong effects were found on Young modulus and rubbery state modulus. As the concentration of LC increases, these mechanical parameters drop significantly together with the glass transition temperature of the polymer showing a plasticizing effect. The results for the glass transition temperatures for the polymer and the LC were confirmed by thermograms obtained by differential scanning calorimetry.

Storage tensile modulus versus temperature of EB‐cured TPGDA/E7 films for different LC concentrations.     

Microwave-assisted synthesis of isosorbide-derived diols for the preparation of thermally stable thermoplastic polyurethane

In order to prepare thermally stable isosorbide-derived thermoplastic polyurethane, the synthesis of two new chiral exo–exo configured diols, prepared from isosorbide, and two types of diphenols (bisphenol A and thiodiphenol) was described. The synthesis conditions were optimized under conventional heating and microwave irradiations. To prove their suitability in polymerization, these monomers were successfully polymerized using 4,4′-diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). Both monomers and polymers have been studied by NMR, FT-IR, TGA, DSC; intrinsic viscosity of polymers has also been determined. The results showed the effectiveness of the synthetic strategy proposed; moreover, a dramatic reduction of the reaction time and an important improvement of the monomers yield using microwave irradiation have been demonstrated. The monomers, as well as the polymers, showed excellent thermal stability both in air and nitrogen. It was also shown that the introduction of sulphur in the polyurethane backbone was effective in delaying the onset of degradation as well as the degradation rate.     

Inner surface modification of halloysite nanotubes and its influence on morphology and thermal properties of polystyrene/polyamide‐11 blends

The asymmetry of halloysite surface chemistry was used to perform a selective modification of its inner surface via grafting of a synthesized styrene/(methacryloyloxy)methyl phosphonic acid copolymer. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA) and pyrolysis gas chromatography/mass spectrometry were used to evidence and quantify the grafting. Then, raw and hybrid nanoparticles were incorporated in polystyrene (PS)/polyamide‐11 (PA11) blends (80/20 and 60/40 wt%). Scanning electron micrographs showed differences in localization of the halloysite nanotubes (HNTs), since raw halloysite is concentrated in the PA11 phase while modified halloysite is also located at the PS/PA11 interface, leading to a better interfacial adhesion between PS and PA11. An inhibiting effect of modified halloysite on PA11 coalescence was evidenced by measuring the particle size distribution of the extracted nodules. Moreover, the presence of modified halloysite at the interface shows an improvement in terms of thermal stability as observed by TGA, but with no significant effects on PA11 crystallization behaviour as shown by differential scanning calorimetry results. Rheological measurements were carried out to study the influence of the surface modification of halloysite on the blend morphology. A gel‐like behaviour was observed for the (60/40 wt%) HNTs reinforced composition that was enhanced in the case of 10% functionalized halloysite. © 2016 Society of Chemical Industry     

Digital image correlation analysis and modelling of the strain rate in metal cutting

In the last eight decades, considerable modelling and computational efforts have been made to predict the strain rate during cutting with the aim of optimizing machining processes. However, the validation of these modelling approaches on a local scale remains excessively limited due to the lack of in-situ measurements and the faulty existing quick-stop tests. This work presents the in-process analysis of the strain rate and strain in the primary shear zone using high speed Digital Image Correlation (DIC) techniques. The comparison of measured and computed results shows the suitability of the DIC techniques and the robustness of the modelling approaches.