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In this work, the effect of different mixing techniques on thermal and mechanical properties of graphene nanoplatelets (GNPs) and graphene nanofibers (GANFs) loaded epoxy nanocomposites was investigated. Three dispersion methods were employed: a high shear rate (HSR), ultrasonication (US) and the fluidized bed method (FBM). The optical microscopy has revealed that the most suitable dispersion, in terms of homogeneity and cluster size, is achieved by implementing the US and FBM techniques, leading to nanocomposites with the largest increase of glass transition temperature, as supported by the DMA analysis data. The fracture toughness results show a general increase of both the critical stress intensity factor (KIC) and the critical strain energy release rate (GIC), likely due to the homogeneity and the low scale dispersion of the carbonaceous nanostructures. Based on the nanocomposite fracture toughness improvements and also assuming a potential large scale up production of the nanocomposite matrix, a single mixing technique, namely the FBM, was employed to manufacture the carbon fiber reinforced composite (CFRC). This method has resulted in being less time-consuming and is potentially most suitable for the high volume industrial production. The CFRCs were characterized in terms of tensile, flexural and interlaminar fracture toughness properties and the results were analyzed and discussed.

The aim of this paper is to study the effect of strain rate on the compressive behavior of the highly cross-linked RTM6 epoxy resin used in advanced aerospace composites. Dynamic compression tests were performed using a split Hopkinson pressure bar, along with reference quasi-static compression tests, to cover a strain rate range from 0.001 to 1035 s−1. Special attention was paid to the optimization of the test methodologies in order to obtain material data free of bias related to the use of different load introduction techniques and sample geometries over the considered strain rate range. In addition, the use of full-field 3D deformation measurements allowed the validation of traditional test and material assumptions. A novel self-alignment tool was developed to enable perfect interfacial contact during compression loading. The 3D digital image correlation technique was used to measure the instantaneous deformation of the sample during compression at different strain rates. Results showed a pronounced strain rate sensitivity of the RTM6 epoxy in compression. The peak yield strength increased with increasing strain rate, while the elastic modulus and Poisson’s ratio in compression were independent of the strain rate. The barreling of the sample in compression, quantified by the barreling ratio, showed an increase during the progression of the compression tests. However, the barreling ratio significantly decreased with the increasing strain rate. Finally, it was shown that neglecting the significant volume change in the yield stages gave rise to a non-negligible underestimation of the strength of the material.

Two different hyperbranched polymer (HBPs) fillers were synthesized and dispersed within an aeronautical graded epoxy matrix as toughening agents. The first typology, identified as HBPG (HBP Glassy) is a glassy polyester characterized by a higher glass transition temperature (Tg) then room temperature (∼90 °C) and obtained by means of bulk polycondensation reaction starting from a diphenolic acid as precursor. The second hyperbranched polymer, labelled HBPR (HBP Rubbery) was a polyamide ester with a Tg of about 20 °C and synthesized by bulk polycondensation of sebacic acid and diisopropanolamine. HBP/epoxy systems were prepared considering two concentration levels, respectively 0.1 and 5 wt%, and the effects on rheological, thermal stability, mechanical properties and fracture toughness were investigated and analyzed in respect to the corresponding neat epoxy. Rheological results revealed that the HBPG filler induces relevant effects on the viscosity of the epoxy matrix compared to HBPR limiting the potential usage of the system for composite manufacturing. Nevertheless, HBPG induces optimal results in term of thermal stability, mechanical and fracture performances, with a limited reduction of the Tg and a higher increase of degradation activation energy along with enhanced fracture behavior as indicated by an enhanced critical stress intensity factor (KIC) and critical strain energy value (GIC). The main result of this work suggests that the HBPG/RTM6 epoxy could be suitably used as polymer matrix for carbon-reinforced composites preserving the advantages of infusion process but at the same time enhancing the matrix-driven mechanical property.

This paper describes the preparation and characterization of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) highly porous monolithic aerogels with a hydrophobic nanoporous–crystalline phase and a hydrophilic sulfonated amorphous phase. The sulfonated aerogels were obtained by the sulfonation of PPO physical gels, followed by the supercritical CO2 extraction of solvents. WAXD and FTIR analysis showed that the nanoporous–crystalline phase was preserved for a degree of sulfonation up to c.a. 35%, allowing a highly volatile organic compound (VOC) sorption capacity. The sulfonated PPO aerogels exhibited a high water sorption capacity, with a water uptake of up to 500 wt%, and faster VOC sorption kinetics from water with respect to unsulfonated aerogels.

We report an innovative fiber optic nano-optrode based on Long Period Gratings (LPGs) working in reflection mode for the detection of human Thyroglobulin (TG), a protein marker of differentiated thyroid cancer. The reflection-type LPG (RT-LPG) biosensor, coated with a single layer of atactic polystyrene (aPS) onto which a specific, high affinity anti-Tg antibody was adsorbed, allowed the label-free detection of Tg in the needle washouts of fine-needle aspiration biopsies, at concentrations useful for pre- and post-operative assessment of the biomarker levels. Analyte recognition and capture were confirmed with a parallel on fiber ELISA-like assay using, in pilot tests, the biotinylated protein and HRP-labeled streptavidin for its detection. Dose-dependent experiments showed that the detection is linearly dependent on concentration within the range between 0 and 4 ng/mL, while antibody saturation occurs for higher protein levels. The system is characterized by a very high sensitivity and specificity allowing the ex-vivo detection of sub ng/ml concentrations of human Tg from needle washouts of fine-needle aspiration biopsies of thyroid nodule from different patients.

This work aimed to investigate the effect of hybrid carbon nanofillers (e.g., carbon nanotubes/carbon nanofibers in the ratio 1:1 by mass) over the electrical and flexural properties for an epoxy matrix and corresponding basalt fibre reinforcing composite (BFRC) subjected to full-year seasonal water absorption. Hydrothermal ageing was performed by full immersion of the tested materials into distilled water according to the following model conditions (seasons). The mechanical properties were measured in three-point bending mode before environmental ageing and after each season. Upon environmental ageing, the relative change of flexural strength and elastic modulus of the epoxy and NC was within 10–15%. For nanomodified BFRCs, the slightly higher effect (approx. by 10%) of absorbed moisture on flexural characteristics was found and likely attributed to higher defectiveness (e.g., porosity, the formation of agglomerates etc.). During flexural tests, electrical resistance of the nanocomposites (NC) and BFRC/NC samples was evaluated. The electrical conductivity for UD BFRC/NC, before and after hydrothermal ageing, was by 2 and 3 times higher than for the NC, accordingly, revealing the orientation of electrically conductive nanoparticles and/or their agglomerates during lay-up manufacturing which was evaluated by the rules of the mixture. Based on all results obtained it can be concluded that the most potentially applicable for damage indication was UD BFRC/NC along fibres since full-year hydrothermal ageing improved its electrical conductivity by approx. 98% and, consequently, the ability to monitor damages was also enhanced.

The effects of temperature and moisture on flexural and thermomechanical properties of neat and filled epoxy with both multiwall carbon nanotubes (CNT), carbon nanofibers (CNF), and their hybrid components were investigated. Two regimes of environmental aging were applied: Water absorption at 70 &deg, C until equilibrium moisture content and thermal heating at 70 &deg, C for the same time period. Three-point bending and dynamic mechanical tests were carried out for all samples before and after conditioning. The property prediction model (PPM) was successfully applied for the prediction of the modulus of elasticity in bending of manufactured specimens subjected to both water absorption and thermal aging. It was experimentally confirmed that, due to addition of carbon nanofillers to the epoxy resin, the sorption, flexural, and thermomechanical characteristics were slightly improved compared to the neat system. Considering experimental and theoretical results, most of the epoxy composites filled with hybrid carbon nanofiller revealed the lowest effect of temperature and moisture on material properties, along with the lowest sorption characteristics.

Summary Syndiotactic polystyrene films and aerogels with nanoporous crystalline phase and sulfonated amorphous phase have been prepared and characterized. The nanoporous nature of the crystalline phase confers to these materials a high solubility of volatile organic compounds (VOCs) from aqueous solutions even at low VOC concentrations while the sulfonation of the amorphous phase enhance the VOC sorption kinetics. These combined properties make these materials particularly interesting for a potential use as a sorption medium to remove traces of pollutants from water. Different aspects relative to the preparation, the structure and the transport properties of these innovative polymeric materials are described.

Metal nanoparticles (NPs) were prepared from acrylamide complex of iron and nickel nitrates by controlled thermolysis at constant temperature in a self-generated atmosphere and used to fabricate epoxy resin nanocomposites. X-ray diffraction performed on the nanoparticles revealed a metal core/polymeric shell structure for the nanoparticles thermolysed at higher temperature as also confirmed by cross analysis of thermo-gravimetrical and vibrating magnetometer data. Optical microscopy was used to investigate the achieved dispersion of the nanoparticles within the uncured resin and transmission electronic microscopy was used to analyse the morphology and the average dimensions of the nanoparticles. Thermal stability of manufactured nanocomposites was studied by thermo-gravimetric analysis in inert and oxidative conditions, reporting that negligible variations are induced by the presence of nanofillers. A complete thermo-mechanical and fracture characterization was carried out to assess the effect of nanoparticles on final nanocomposite system. A slight increase of the modulus is recorded at room temperature whereas a significant variation is induced for higher temperature. The presence of nanoparticles induces a global increase in the fracture energy of nanocomposite associated to different failure mechanisms. Magnetic data indicate that iron particles based nanocomposites display room-temperature ferromagnetic behaviour with saturation magnetization and coercivity depending on the diameter of the metal core.

A novel hyperbranched poly(amide-ester)s (HBP) has been synthesized through the AB 2 approach in one-step polycondensation without solvents. The synthesized HBP has been characterized and used as filler for epoxy resin with the aim obtain materials which exhibit improved toughness. Composites containing 6% and 12% wt/wt of HBP in diglycidylether of bisphenol A (DGEBA) were produced and characterized. Results obtained from DMA tests showed that HBP has good compatibility with the epoxy resin. Impact tests proved that composites containing 12% HBP showed an improvement of about 25% on impact strength with respect to neat DGEBA. Moreover, adhesive properties were evaluated in terms of the lap-shear strength value of composite joints bonded using the investigated blend. Results showed an improvement of shear strength value of DGEBA added with 12% HBP with respect to neat DGEBA. The water uptake behavior was also evaluated.

The integration of a tetrakis(4-sulfonatophenyl)porphyrin (TPPS) thin film with optical fiber technology is obtained via a non-conventional procedure consisting in a UV-light induced deposition. This leads to the growth of TPPS thin films right at the core region of the fiber end. The simplicity and cost effectiveness of this procedure, as well as the potential of porphyrins as functional materials, enable the design of novel active and passive in-fiber devices. Here, the presence of intense, narrow bands in the reflected spectra is successfully exploited to detect corrosive or toxic vapors, such as strong volatile acids and bases, at room temperature.

Proton conductivity of innovative ionomeric membranes based on partially sulfonated syndiotactic polystyrene (SsPS) was investigated. The membranes were prepared with various levels of sulfonation by chlorosulfonic reaction on sPS films, in its clathrate form, obtained by solution-casting. The actual sulfonation degree of sPS membranes was evaluated by elemental analysis and their proton conductivity was measured using a galvanostatic four-points-probe electrochemical impedance spectroscopy technique. The dependence of conductivity on the level of sulfonation, hydration condition, and temperature was studied. At higher sulfonation degrees, SsPS membranes showed the best performance in vapor phase at 100% RH. In particular, the best SsPS membrane with sulfonation degree about 26 mol% exhibited conductivity equal to 8.8 × 10−2 Ω−1 cm−1 at 31.5 °C. This property is stable during time and increases with temperature. For the membranes with the highest degree of sulfonation, we measured a methanol permeability ...

The incorporation of siloxane networks in sulfonated polystyrene membranes by the sol-gel process was used to explore the possibility of developing low cost membrane for direct methanol fuel cells. A precursor solution of a hydrophobic siloxane network was allowed to diffuse and react into sulfonated syndio-polystyrene ionomeric membranes. The organic-inorganic hybrid domains so produced were able to reduce considerably the swelling of the ionomeric polymer in water, thereby increasing the dimensional stability of membranes. The physical and chemical properties of the sulfonated and hybrids membranes were examined by thermogravimetric analysis (TGA), infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS) analysis. The water uptake and the ionic conductivity were also evaluated at temperatures up to 60° C. It was found that both the unmodified sulfonated membranes and the corresponding hybrid exhibited a two-phase morphology, consisting of crystalline lamellar domains embedded in the amorphous ionomeric polymer, featuring segregated hydrophobic/hydrophilic domains with characteristic separation lengths ranging between 3.9 and 1.7 nm. The presence of inorganic domains not only increased the dimensional stability of the membrane, by reducing the water uptake, but also decreased the rate of methanol crossover. Furthermore it was found that the inorganic network stabilizes the membrane morphology, enhancing the retention of proton conductivity after aging in water. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

We report here on a reflection-type long period fiber grating (RT-LPG) biosensor for the fast detection of class C (AmpC) β-lactamases (BLs), actually considered as one of the most important source of resistance to β-lactam antibiotics expressed by resistant bacteria. A standard LPG working in transmission configuration is first transformed in a more practical probe working in reflection mode and successively coated with a primary high refractive index (HRI) overlay of atactic polystyrene (aPS) in order to increase its surrounding refractive index sensitivity (SRI) in biological solutions. The aPS-coated RT-LPG is then coated by a secondary layer of poly(methylmethacrylate)- co -methacrylic acid (PMMA- co -MA) in order to provide the necessary surface functionalities to promote a stable covalent bioreceptors immobilization. The BLs detection has been performed by using the 3-aminophenylboronic acid (3-APBA) as biorecognition element, due to its excellent inhibition properties against class C BLs and specificity. Results here provided demonstrate that the proposed label free biosensor is capable of reliable detection of purified AmpC BLs in phosphate buffer solutions (PBS) with concentrations as low as one hundred nM, with a lowest limit of detection (LOD) of the order of a few tens of nM. The real effectiveness of the proposed biosensor has been also confirmed in lysate samples, which contain Escherichia coli bacteria overexpressing AmpC BLs.

As-received and pre-treated sepiolite/epoxy systems, characterised by an inorganic content from 2 to 10 wt.%, were investigated in order to assess induced-filler effect on degradation and fire behaviour. Thermogravimetrical results show that the thermal stability of the hosting epoxy, is slightly affected by the presence of sepiolite for both typologies; whereas, changes induced in char morphology by the pre-treated clay will significantly affect the fire behaviour of the final nanocomposite. Modelling of thermo-gravimetrical results in air atmosphere, by means of Kissinger procedure, shows a noteworthy reduction of activation energies associated with each degradation steps, especially at highest sepiolite content either by using as-received and pre-treated inorganic filler. This substantially indicates that the presence of sepiolite shorten the whole degradation process on the temperature scale. On the other hand, the different morphology of the char layer during the burning process can have relevant flame retardant effects acting on both condensate and vapour phase. Analysing the cone calorimetric data, a reduction of about 27% of the peak of heat release rate for the highest sepiolite percentage is measured and the burning total period is increased thus confirming that sepiolite when pre-treated represents a valid fire retardant inorganic filler for such a system.

This Letter deals with a feasibility analysis for the development of radiation-tolerant fiber-optic humidity sensors based on long-period grating (LPG) technology to be applied in high-energy physics (HEP) experiments currently running at the European Organization for Nuclear Research (CERN). In particular, here we propose a high-sensitivity LPG sensor coated with a finely tuned titanium dioxide (TiO₂) thin layer (~100 nm thick) through the solgel deposition method. Relative humidity (RH) monitoring in the range 0%-75% and at four different temperatures (in the range -10°C-25°C) was carried out to assess sensor performance in real operative conditions required in typical experiments running at CERN. Experimental results demonstrate the very high RH sensitivities of the proposed device (up to 1.4 nm/% RH in correspondence to very low humidity levels), which turned out to be from one to three orders of magnitude higher than those exhibited by fiber Bragg grating sensors coated with micrometer-thin polyimide overlays. The radiation tolerance capability of the TiO₂-coated LPG sensor is also investigated by comparing the sensing performance before and after its exposure to a 1 Mrad dose of γ-ionizing radiation. Overall, the results collected demonstrate the strong potential of the proposed technology with regard to its future exploitation in HEP applications as a robust and valid alternative to the commercial (polymer-based) hygrometers currently used.

Sepiolite/epoxy systems, characterised by an inorganic content from 2% to 10% by weight, were tested by using different experimental techniques in order to assess the effects thermo-mechanical and fracture behaviour. It was found that filler dispersion is independent on the type of sepiolite used, i.e. hydrated and de-hydrated, whereas the addition of hydrated sepiolite strongly increases the viscosity of the final suspension. Mechanical properties have been investigated and discussed. The conservative modulus of the sepiolite/epoxy system increases as much as 21% and 94% respectively, at 35 °C and 200 °C respect to the unfilled polymer, with the incorporation of 10 wt% of sepiolite, both hydrated and dehydrated, with a slightly increasing of the corresponding glass transition temperature. The effect of sepiolite on the coefficient of thermal expansion lead to a variation in both glassy and rubbery region, respectively of about 7–8% and 9%. Fracture toughness analysis revealed that the critical stress intensity factor negligibly changes by increasing the sepiolite content, whereas the critical strain energy release rate (GIC) reaches an noteworthy value around 30% higher than neat epoxy.

1-Butene polyinsertion promoted by two typical C 2 -symmetric zirconocene catalysts (i.e. rac-ethylenebis(1-indenyl)ZrCl 2 (1) and rac-dimethylsilylbis(1-indenyl)ZrCl 2 ) (2) was investigated under both hydrooligomerization and polymerization conditions and compared with that of propene. It was found that, in spite of a similar regiospecificity for the two monomers, the fraction of dormant sites is higher in 1-butene polymerization, as a result of a (much) lower reactivity of a 2,1 last-inserted unit. Accordingly, in the investigated cases, 2,1 units of 1-butene were not incorporated in the growing chains but either isomerized to 4,1 units or remained at the chain end until they underwent chain transfer via β-hydrogen elimination. Experimental evidence is also presented of an epimerization reaction of the growing poly(1-butene) chain with a 1,2 last-inserted unit, leading to a decrease of polymer stereoregularity with decreasing monomer concentration.

The polymorphic behaviour of isotactic poly(4-methyl-1-pentene) is discussed on the basis of conformational energy calculations. A preliminary model of packing of form III is presented. Chains having helical conformations with 4/1 symmetry are packed in a tetragonal body-centered unit cell with axesa = 19.38 A,c = 6.98 A.

The polycondensation of sebacic acids and ω-amino alcohols by microwave irradiation was studied. The results were compared to those obtained from conventional melt polycondensation of poly(amide-ester)s. It was found that the reaction proceeded at a much higher rate upon microwave irradiation. A high yield of thermally stable poly(amide-ester)s was obtained. The microwave-synthesized compounds were fully characterized by FTIR and 1H-NMR spectroscopy, gel permeation chromatography, and a solubility test. The thermal properties of the poly(amide-ester)s also were investigated. The results showed that the chemical-physical properties of the polymers were in good agreement with those of polymers obtained by conventional synthesis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1952–1958, 2007

This contribution presents distributed and multipoint fiber-optic monitoring of cryogenic temperatures along a superconducting power transmission line down to 30 K and over 20 m distance. Multipoint measurements were conducted using fiber Bragg gratings sensors coated with two different functional overlays (epoxy and poly methyl methacrylate (PMMA)) demonstrating cryogenic operation in the range 300-4.2 K. Distributed measurements exploited optical frequency-domain reflectometry to analyze the Rayleigh scattering along two concatenated fibers with different coatings (acrylate and polyimide). The integrated system has been placed along the 20 m long cryostat of a superconducting power transmission line, which is currently being tested at the European Organization for Nuclear Research (CERN). Cool-down events from 300-30 K have been successfully measured in space and time, confirming the viability of these approaches to the monitoring of cryogenic temperatures along a superconducting transmission line. (C) 2015 Optical Society of America