A review of the analysis and characterisation of polymeric glass fibre sizings

Glass fibre reinforcements form the backbone of a composites industry. Possibly the most critical component involved in the manufacture of glass fibres and their composites is the fibre sizing. Yet because of the intense level of secrecy surrounding size formulations there are few who have more than a superficial understanding of sizings. Composite developers and researchers have a growing need for practical tools which can assist with the understanding of the nature and role of sizings on the glass fibres which reinforce their composites. This work reviews some of the most relevant articles from the widely dispersed literature around the analysis and characterisation of these polymeric sizings. The review covers the analysis and characterisation of the polymeric sizing layer on the glass fibre surface using high vacuum surface analysis techniques, thermal analysis, atomic force microscopy based techniques, surface energy analysis, infrared methods, and combined multiple analysis techniques. The conclusions highlight the fragmented nature of the knowledge base on sizings and the lack of reliable and reproducible reference materials on which to build real progress in the understanding of this critical technology.     

Preparation of magnetic nanoparticles by the use of self-assembled fluorinated oligomeric aggregates—A new approach to the dispersion of magnetic particles on poly(methyl methacrylate) film surface

Fluoroalkyl end-capped acrylic acid oligomer-encapsulated magnetic nanoparticles were prepared by the coprecipitation of aqueous ferric and ferrous ions in the presence of the corresponding oligomers under alkaline conditions. The dynamic light scattering measurements showed that these fluorinated oligomer magnetic nanoparticles were encapsulated in the self-assemblies of fluoroalkyl end-capped oligomers. Fluoroalkyl end-capped oligomer-encapsulated magnetic nanoparticles thus obtained were applied to the dispersion of magnetic particles on the poly(methyl methacrylate) film surface to exhibit not only the surface active property imparted by fluorine but also magnetic behavior toward a permanent magnet.     

A new approach to describe the skin surface physical properties in vivo

In the present paper, we describe a new mechanical method characterising the physico-chemical properties of human skin and their variations along with liquid exposure scenario to the skin surface. A specific bio-tribometer has been developed to study the physical properties of the skin in vivo by measuring the maximum adhesion force between the skin and the bio-tribometer. We showed that the lipidic film present on skin surface was responsible for skin adhesion due to capillary phenomena. The measure of pull-off force between skin and bio-tribometer has permitted to estimate the liquid/vapour surface tension of the lipidic film (γ_LV ≈ 6.3 mJ/m² in 30-year-old volunteer). The kinetic of sorption/desorption (sorption means indifferently adsorption and absorption process) of distilled water from the skin has been observed through the variation of the indenter/skin pull-off force versus time after distilled water application to the skin surface. This permits to follow in real time the variation of the skin physico-chemical properties after liquid application onto the skin surface. Finally, the increasing of skin friction coefficient after distilled water application onto skin surface was explained by the capillary adhesion force between the probe and the skin.     

Analytical approach on surface active agents in the environment and challenges

Surface active agents (SAAs) are a class of compounds, which is used in variety of products such as detergents, fabric softeners, soaps, paints, adhesives, inks and anti-fogs. After the use of these products containing surfactants are disposed in water reservoirs. The separation and determination of surfactants from complex matrices become challenging for analytical chemists. The fundamentals on separation, preconcentration and analysis of surfactants employing different analytical instrumental techniques for qualitative and quantitative determination of surfactants in environmental samples are discussed. In addition, this compiled work enhanced our knowledge in learning about pathway mechanisms and the degree of their environmental loads. We also discussed the different aspects of method validation in the framework of quality control (QC) and quality assurance (QA). This review provides information on levels of SAAs in various environmental samples including soil, sediments, sewage wastewater, river wastewater and aerosols worldwide.     

Effect of local microstructure on the indentation induced damage of a fiber reinforced composite

Multicycle grid nanoindentation tests, combined with high resolution Scanning Electron Microscopy (SEM) and Scanning Probe Microscopy (SPM) observations, were applied on a commercial Carbon Fiber (CF) reinforced epoxy matrix composite in order to study the induced damage mechanisms with respect to: (a) the orientation of the CFs relative to the surface and (b) the CF packing density. Normal to the surface CFs showed a multiple cracking pattern, those forming 45° showed distinct cracking, while CFs parallel to the surface did not suffer cracking. CF detachment from the epoxy matrix was observed in all cases. Pop-in type discontinuities were observed only in the samples where cracking ensued, as revealed through SEM and SPM observations. The load to induce CF cracking increased with increase of the matrix pocket area. Elastic modulus, hardness and significance of elastic deformation as an indentation energy absorbing mechanism, were reduced right after pop-in.     

Polymer Modification Strategy to Modulate Reaction Microenvironment for Enhanced CO2 Electroreduction to Ethylene

Modulation of the microenvironment on the electrode surface is one of the effective means to improve the efficiency of electrocatalytic carbon dioxide reduction (eCO₂RR). To achieve high conversion rates, the phase boundary at the electrode surface should be finely controlled to overcome the limitation of CO₂ solubility in the aqueous electrolyte. Herein, we developed a simple and efficient method to structure electrocatalyst with a superhydrophobic surface microenvironment by one-step co-electrodeposition of Cu and polytetrafluoroethylene (PTFE) on carbon paper. The super-hydrophobic Cu-based electrode displayed a high ethylene (C₂H₄) selectivity with a Faraday efficiency (FE) of 67.3 % at −1.25 V vs. reversible hydrogen electrode (RHE) in an H-type cell, which is 2.5 times higher than a regular Cu electrode without PTFE. By using PTFE as a surface modifier, the activity of eCO₂RR is enhanced and water (proton) adsorption is inhibited. This strategy has the potential to be applied to other gas-conversion electrocatalysts.     

A simple approach for the synthesis of new classes of dithiocarbamate-linked peptidomimetics

An efficient protocol for the synthesis of a new series of dithiocarbamate-linked peptidomimetics is described. The in situ generated dithiocarbamic acid intermediate formed by the reaction of an amino acid ester and carbon disulfide in the presence of triethylamine was treated with N-protected amino alkyl iodide to afford title compounds 3a-g in good to moderate yields. The synthesis of N-Fmoc-protected tripeptidomimetics 4a-e containing two dithiocarbamate linkages is also described. The protocol was further extended to synthesize N,N′-orthogonally protected dithiocarbamate-linked dipeptidomimetics 7a-c as well. The mild reaction conditions and non-toxic reagents are the advantages of the present method.     

Surface acoustic waves for the characterization of BN-coated fibres observed by Brillouin light scattering

The observation of acoustic phonons located at the surface of uncoated fibres or guided in thin films deposited on fibres by Brillouin light scattering spectroscopy (BLS) is reported. The BLS technique is non-destructive and non-intrusive and is well applicable to non-planar sample geometries. Investigations were carried out on bundles of commercially available carbon fibres, in which a single fibre was 5 m in diameter. With regard to the detected surface acoustic excitations, each fibre can be considered as an infinite halfspace owing to the large ratio of fibre diameter to wavelength. The shear modulus, which is highly relevant for the intended technical application, was determined by measurement of the Rayleigh mode phase velocity of the uncoated fibres. These fibre bundles were coated with boron nitride (BN) in a continuously driven thermal chemical vapour deposition (CVD) process using trimethyl borate and ammonia as precursors. In comparison to carbon, BN is expected to improve the mechanical properties of fibre-reinforced composites such as fracture toughness at high temperatures. The measured velocity dispersion of the Rayleigh mode of this film-on-substrate system permitted the comparison of the shear stiffness of the carbon fibre and of the BN film material. The results evidence the desired effect of a distinct stiffness reduction of the coated fibre relative to the uncoated fibre in the near-surface region. Additional information can be obtained on the homogeneity of the deposition across the whole fibre bundle.     

A new approach to the chiral separation of novel diazenes

Two new types of potential liquid‐crystalline azo compounds were synthesized in the form of racemic mixtures and as the individual S enantiomers. Both materials consisting of two substituted aromatic rings in the molecular core and one chiral center at the aliphatic moiety showed mesomorphic behavior. The separation of the R and S enantiomers by chiral high‐performance liquid chromatography was unsuccessful when the azo compounds were in their natural E state. However, the irradiation of the compounds in the solution by UV light led to an almost quantitative transition to their Z forms. The chromatographic behavior of the compounds in their Z forms was significantly different, and partial separation of the individual enantiomers on chiral polysaccharide‐based stationary phases was obtained. Thus, the proposed procedure represents a novel approach to the enantioseparation of chiral diazenes.     

A new approach to the synthesis of carbon chains capped by metal clusters

Reactions of Co₃(μ₃-CBr)(μ-dppm)(CO)₇ with {Au[P(tol)₃]}₂{μ-(CC)_n} (n=2–4) have given {Co₃(μ-dppm)(CO)₇}{μ₃:μ₃-C(CC)_nC} [n=2 (1), 3 (2), 4 (3)] containing carbon chains capped by the cobalt clusters. Tetracyanoethene reacts with 2 to give {Co₃(μ-dppm)(CO)₇}₂{μ₃:μ₃-C(CC)₂C[=C(CN)₂]C[=C(CN)₂]C} (4). X-ray structural characterisation of 1, 3 and 4 are reported, that for 3 being the first of a cluster-capped C₁₀ chain.     

Self-organization of dipeptide-grafted polymeric nanoparticles film: A novel method for surface modification

Novel dipeptide-grafted polymeric nanoparticles were prepared by grafting the dipeptide (Gly-Gly) to a block copolymer backbone, comprised of styrene-alt-(maleic anhydride) and styrene. In aqueous solution PSt₁₃₀-b-P(St-alt-MAn)₅₈-g-GlyGly₂₆ formed stable dispersed spherical aggregates of ca. 75 nm. The critical micelle concentration for the dipeptide-grafted block copolymer self-aggregates was 6.3 × 10⁻³ mg mL⁻¹. The zeta-potential of the aggregates was estimated experimentally. The dispersed polymer nanoparticles effectively self-organized to form stable nanoparticle thin films on hydrophobic solid surfaces, such as octadecyltrichlorosilane modified glass (OTS-G). As the ionic strength and temperature of the polymer suspension increased the surface coverage of the nanoparticle film increased and its hydrophobicity (water contact angle) decreased. Significantly less bovine serum albumin (BSA) adsorbed to nanoparticles modified surfaces with compared OTS-G surfaces. Diglycine grafted polymer nanoparticles have the potential to be used as a novel platform to study protein-protein interactions and to control fouling.     

Recycling of carbon fibre reinforced polymeric waste for the production of activated carbon fibres

Composite waste composed of carbon fibres and polybenzoxazines resin has been pyrolysed in a fixed bed reactor at temperatures of 350, 400, 450, 500 and 700 °C. Solid residues of between 70 and 83.6 wt%, liquid yields 14 and 24.6 wt% and gas yields 0.7 and 3.8 wt% were obtained depending on pyrolysis temperature. The derived pyrolysis liquids contained aniline in high concentration together with oxygenated and nitrogenated aromatic compounds. The pyrolysis gases consisted mainly of CO₂, CO, CH₄, H₂ and other hydrocarbons. The carbon fibres used in the composite waste were separated from the char of the solid residue via oxidation of the char at two different temperatures and investigated for their mechanical strength properties. The carbon fibres recovered from the sample pyrolysed at 500 °C and oxidised at 500 °C exhibited mechanical properties which were 90% of that of the original virgin carbon fibres. Steam activation of the recovered carbon fibres was carried out at 850 °C at different times of activation. The effect of activation time on BET surface area, activated carbon fibres yield, porosity and the morphological structure of activated carbon fibres was evaluated. A maximum BET surface area of over 800 m² g⁻¹ was obtained for the activated carbon fibres produced at 850 °C for 5 h of activation. Nitrogen adsorption-desorption isotherms showed that the adsorption capacity increased as the activation time increased up to 5 h of activation and then after that decreased.     

Surface segregation of polypeptide-based block copolymer micelles: An approach to engineer nanostructured and stimuli responsive surfaces

We describe the surface segregation of polypeptide-based block copolymer micelles to produce stimuli-responsive nanostructures at the polymer blend/air interface. Such structures were obtained by simultaneous surface migration and self assembly at the surface of diblock copolymer/homopolymer blends. We employed blends composed of homopolymer (PS) and an amphiphilic block copolymer polystyrene-b-poly(l-glutamic acid) (PS-b-PGA). The surface was functionalized based on the preferential segregation to the polymer blend/air interface of the hydrophilic PGA block of the diblock copolymer upon annealing to water vapor. The surface migration of the diblock copolymer to the interface was demonstrated both by XPS and contact angle measurements. As a consequence, the PGA interfacial attraction leads to a large surface excess on diblock copolymer which in turn, through macrophase and microphase separation, produced separated domains at the surface with regions composed either of homo or block copolymer. Herein we demonstrate that the use of asymmetric diblock copolymers with a higher content in PS lead to spherical micellar assemblies randomly distributed at the surface. As observed by AFM imaging the blend composition, i.e. the amount of block copolymer within the blend influences the density of micelles at the surface. Finally, when exposed to water, the pH affects the surface morphology. The PGA segments are collapsed at low pH values and extended at pH values above 4.8, thus inducing variations on the topography of the films at the nanometer scale.     

A new surface roughening method for glass capillary columns. Sodium chloride deposition from suspension

A method is described for roughening the surface of glass capillary columns for subsequent coating with polar stationary phases. A suspension of sodium chloride, obtained by addition of a saturated solution of sodium chloride in methanol to 1,1,1-trichloroethane, is passed through the column at velocities of 1–5 cm/s. During passage of the suspension, particles of sodium chloride deposit spontaneously on the column wall. The amount of sodium chloride deposited on the column wall is a function of the volume of the suspension passed through and of the contact time of the suspension and the column wall. Ultimately the amount of sodium chloride per unit surface area approaches a maximum. Columns covered with this maximum amount of sodium chloride were prepared with high reproducibility and coated with a number of polar stationary phases. Various factors that influence the stability of the suspension and the deposition of sodium chloride are discussed and minimum requirements are given. A theoretical model is proposed for the mechanism of deposition of sodium chloride particles on the glass wall.     

Electrical surface resistivity of conductive polymers - A non-Gaussian approach for determination of confidence intervals

Polyanilines doped with different acids (HCl, H₂SO₄ and dodecylbenzenesulfonic acid, DBSA) were prepared and their surface electrical conductivities were characterized in a four-probe device, connected to a real-time data acquisition board. Collected data were synchronized and conductivity calculations were performed. The conductive behavior of the polyanilines was investigated along the electrification time. This allowed for introduction of a non-Gaussian technique for determination of the confidence intervals of surface resistivity data. It is shown that the distribution of experimental surface resistivity data does not follow a normal probability distribution function (PDF). Thus, ordinary assumptions related to normal distribution of the experimental errors are wrong and must be corrected for proper determination of the confidence limits of measured resistivity values. It is shown here that confidence limits of resistivity values are asymmetrical and that distribution of experimental values can follow multimodal distributions.     

Application of ammonia intermittent temperature-programmed desorption to evaluate surface acidity of tungsten oxide supported on activated carbon

Intermittent temperature-programmed desorption of ammonia was used to study the strength and population of surface acid sites of tungsten oxide supported on activated carbon pretreated at 350 and 700 degrees C. Catalysts pretreated at 350 degrees C showed two types of surface acid sites and desorption occurred with free readsorption until a temperature of around 300 degrees C was reached. Pretreatment at 700 degrees C produced three different states of ammonia adsorbed on the catalysts and desorption occurred with free readsorption.     

A new approach to decoherence and momentum rescaling in the surface hopping algorithm

As originally proposed, the fewest switches surface hopping (FSSH) algorithm does not allow for decoherence between wavefunction amplitudes on different adiabatic surfaces. In this paper, we propose an inexpensive correction to standard FSSH dynamics wherein we explicitly model the decoherence of nuclear wave packets on distinct electronic surfaces. Our augmented fewest switches surface hopping approach is conceptually simple and, thus far, it has allowed us to capture several key features of the exact quantum results. Two points in particular merit attention. First, we obtain the correct branching ratios when a quantum particle passes through more than one region of nonadiabatic coupling. Second, our formalism provides a new and natural approach for rescaling nuclear momenta after a surface hop. Both of these features should become increasingly important as surface hopping schemes are applied to higher-dimensional problems.     

Thermal degradation of polymers to polymeric carbon--an approach to the synthesis of new materials

One hundred years ago, Edison succeeded in preparing carbon fibers for his incandescent lamp bulb by thermal decomposition of natural polymeric fibers. Ten years ago, progress reports about “Novel Forms of Carbon” predicted outstanding properties and promising new applications for the carbonization products of synthetic polymers. Research and development in this field have been promoted by the problems of conventional technology (shortages of raw material and energy, pollution problems). Polymeric carbon materials—prepared by thermal degradation of synthetic polymers—exhibit a special ribbon-like microstructure. They will provide the chemist with many challenges.     

Effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide substrates for polymer LEDs

The effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide (ITO) substrates and the changes in surface properties of treated ITO substrates with ageing time were investigated by X-ray photoelectron spectroscopy (XPS), contact angle and surface free energy measurements. Experimental results show that oxygen plasma treatment increases the oxygen concentration, decreases the carbon concentration, and enhances the surface free energy and polarity, and thereby improves the surface properties of ITO substrates. However, the improved ITO surface properties tended to decay and the surface free energy decreased, with ageing time. In addition, the ageing effect of treated ITO substrates on the performance of polymer light-emitting diodes (LEDs) was studied with respect to the driving voltage, electroluminescent luminance and efficiency. We observe that the ITO substrates aged for various times result in significant differences in optical and electrical characteristics which become worse as the ageing time increases. The optical and electrical performance of polymer LEDs is closely related to the surface properties of ITO substrate and the interface characteristics of ITO/polymer.     

A new original approach to the design of anticancer drugs based on energy-rich quadricyclanes

Russian Chemical Bulletin - Quadricyclane derivatives are shown for the first time to be promising for application as anticancer drugs. The efficiency of such cage compounds is mainly due to...