Photo-polymerisation of composite resins measured by micro-Raman spectroscopy

The micro-Raman spectroscopy was used for measuring the photo-polymerisation of composite resins. The elevated spatial resolution of the technique revealed surface non-homogeneities via the intensity variations of a strong band at 1400 cm⁻¹ and the presence of weak bands around the CC and CO stretching frequencies. Values of the degree of monomer conversion (DC) were determined for samples of Z100 commercial composite irradiated with different wavelength laser beams. Two methods were used for obtaining DC values. The first one exploits band decompositions in the spectral region of interest around 1608 and 1637 cm⁻¹. The non-uniqueness of the decomposition introduces relevant uncertainties, which are amplified by unwanted weak bands. An alternative method, avoiding any fit procedure and exploiting the band shape conservation under irradiation, was found producing more reliable results. The 632 nm line of the He-Ne laser was used as an exciting source. The measurements of the DC versus time are reported for three different wavelengths of the irradiation light. Preliminary studies of the CO stretching bands are also reported. Their intensities decrease under irradiation and there are indications of a behaviour similar to that of the CC aliphatic band.     

Phase separation in epoxy-copolyethersulphone blends: morphologies and local characterisation by micro-Raman spectroscopy

This study was aimed at using micro-Raman spectroscopy for the local characterisation of phase separated blends based on epoxy polymer and copolyethersulphone thermoplastic. The morphologies developed in the blends containing 25% by weight of thermoplastic were studied. The calibrations of the Raman data for the determination of the copolyethersulphone content and the epoxide conversion are presented in this paper and their applicability for spatially resolved Raman characterisation discussed. From spectra collected in both phases after increasing cure times, the evolution of the copolyethersulphone content in each phase was quantitatively determined, whilst a qualitative evolution of the epoxide conversion was obtained. To our knowledge, this study provided for the first time direct measurements of phase characteristics in thermoset-thermoplastic blends.     

Femtosecond laser impact on calcium phosphate bioceramics assessed by micro-Raman spectroscopy and osteoblastic behaviour

The present work is an investigation of the biological response to the presence of grooves 3?μm deep, 15?μm wide and spaced by 100?μm, produced with femtosecond laser on β-tricalcium phosphate (β-TCP). The heat affected zone generated by the laser irradiation was investigated. Micro-Raman spectroscopy showed a transformation from β-TCP phase into α-TCP phase, localised inside the grooves. The X Ray Diffraction analyses, correlated with micro-Raman data, confirmed that the use of femtosecond pulsed laser enables to limit the thermal impact. A selection of optimised process parameters allowed to obtain β-TCP micro-patterned surfaces avoiding any phase transformation. The increase of the wettability with the micro-patterning, compared to smooth surfaces, was highlighted. An improvement of the osteoblastic proliferation was also demonstrated. Finally, the tendency of cell elongation along the grooves direction showed the ability of osteoblastic cells to adapt their morphology to the support topography on which they grow.     

Microdomain structure and chain orientation in polypropylene/polyethylene blends investigated by micro-Raman confocal imaging spectroscopy

Compositional domain structure of blends of isotactic polypropylene with linear polyethylene and chain orientation of neat polymers and of the blends were assessed by micro-Raman confocal imaging spectroscopy and FT Raman spectroscopy. The results were correlated with polarised photoacoustic FTIR and with DSC. The surface and inner parts of compression-moulded, injection-moulded and drawn specimens were compared. Polymer domains in the blends and domains of different orientation were identified. The larger size of the polymer domains and lower chain orientation in the core of the specimens prepared by injection-moulding were explained by different cooling conditions of the melt. Possibilities and limitations of the micro-Raman confocal spectroscopy method were discussed.     

Scanning electron microscopy and micro-Raman spectroscopy of slip layers of Hellenistic ceramic wares from Dorylaion/Turkey

Anatolia (Asia Minor) was inhibitated by several civilizations during the history. Dorylaion at Eski?ehir/Turkey, an ancient site, is on the crossroads of many ancient civilizations. Artifacts belonging to different historical periods and cultures have been uncovered during the excavations carried out there since 1989. One of the two important groups of ceramic findings uncovered in these excavation works is the moldmade bowls, familiarly known as the Megarian bowls and the other is the West Slope wares. Both types of wares were probably the fashion cups around the east Mediterranean basin of the Hellenistic period. In this study, an attempt was made to enlighten the technological parameters and production technology of selected Megarian bowls and West Slope wares by characterizing their slip layers. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) were performed for microstructural and microchemical characterization. Micro-Raman spectroscopy was further applied for assessing the mineralogical components. The slip layers of both wares have similar elemental diversity, apart from the fact that the West Slope wares have more iron content than the Megarian bowls. The iron rich composition of the slip layers in different colors showed that hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃) and magnetite (Fe₃O₄) are the principal coloring agents for the slip layers of the investigated Hellenistic ceramic wares. However, firing conditions affecting the formation and the abundance of these minerals were probably adjusted in order to obtain the desired color.     

Synthesis of rodlike polysiloxane with hexagonal phase by sol-gel reaction of organotrialkoxysilane monomer containing two amino groups

A higher-ordered polysiloxane was prepared by the sol-gel reaction of (3-(2-aminoethylamino)propyl)trimethoxysilane in a hydrochloric acid aqueous solution without using any surfactants. The X-ray diffraction profile of the resulting polysiloxane showed three peaks with the d-value ratio of 1:1/√3:1/2, indicating that this polysiloxane has a hexagonal phase. The peaks shifted by changing the humidity. Therefore, we estimated that this hexagonal phase came from the stacking of a rodlike polymer with a Si-O-Si framework at the core and ammonium groups extruding outside. The TEM image of the polysiloxane showed a stripe pattern indicating an ordered arrangement. Because one repeating unit of the present polysiloxane has two ammonium groups, the ion-exchange capacity of this polysiloxane and viscosity of its aqueous solution were larger than those of the previous polysiloxane with single-ammonium group.     

Temperature and strain registration by fibre-optic strain sensor in the polymer composite materials manufacturing

ABSTRACT

The presence of process-induced strains induced by various manufacturing and operational factors is one of the characteristics of polymer composite materials (PCM). Conventional methods of registration and evaluation of process-induced strains can be laborious, time-consuming and demanding in terms of technical applications. The employment of embedded fibre-optic strain sensors (FOSS) offers a real prospect of measuring residual strains. This paper demonstrates the potential for using embedded FOSS for recording technological strains in a PCM plate. The PCM plate is manufactured from prepreg, using the direct compression-moulding method. In this method, the prepared reinforcing package is placed inside a mould, heated, and then exposed to compaction pressure. The examined technology can be used for positioning FOSS between the layers of the composite material. Fibre-optic sensors, interacting with the material of the examined object, make it possible to register the evolution of the strain process during all stages of polymer-composite formation. FOSS data were recorded with interrogator ASTRO X 327. The obtained data were processed using specially developed algorithms.     

Hydrothermal synthesis and polarized micro-Raman spectroscopy of copper molybdates

Conventional and microwave-assisted hydrothermal methods were used to synthesize Cu₃(MoO₄)₂(OH)₂ ceramics. Different experimental conditions of temperature, time and precipitation rate were employed to explore the growth mechanisms, structural and morphological properties of the obtained copper molybdates. The use of microwave-assisted reactors at 150?°C/10–30?min produced a mixture of copper molybdate hydrates, while only Cu₃(MoO₄)₂(OH)₂ was obtained by using microwave processing at longer times (above 120?min) or conventional hydrothermal reactors (110–250?°C/24?h). Experiments conducted after fast and slow coprecipitation rates resulted in different crystallographic phases and morphologies. Flower-like and rod-like micrometer-sized ceramics were produced with high anisotropy and single-crystalline nature. A better understanding on the growth mechanisms, as well as on the structural and morphological characteristics of copper molybdates was attained. Based upon the relative enhancement of Raman bands in parallel or in perpendicular configuration, a symmetry assignment of 34 (17A_g + 17B_g) external modes for Cu₃(MoO₄)₂(OH)₂ ceramics (42 bands are expected) was possible. Besides, five (of six possible) internal OH-stretching modes were identified in the spectral region above 3200?cm^?1.     

Fabrication and distribution characteristics of polyurethane/single-walled carbon nanotube composite with anisotropic structure

A polyurethane/single-walled carbon nanotube (SWCNT) composite with anisotropic structure is synthesized by two-step process. The effects of external force during the curing process of the composite as well as the tensile stress on the distribution of the SWCNTs in the matrix have been examined by using field-emission scanning electron microscope. The microstructure analysis results indicate that the different distributions of the SWCNTs in the matrix have appeared along two orthogonal directions for the composite samples.     

Epitaxial polymer crystal growth influenced by partial melting of the fiber in the single-polymer composites

We report dynamic Monte Carlo simulations of polymer melt crystallization induced by the same species of the fiber. We found that partial melting on the lateral surface of the fiber postpones the epitaxial crystal growth of the matrix, while the crystal growth rate has been little affected. The delay can be attributed to the recrystallization on the lateral surface of the fiber due to the prior melting. In addition, we observed the highly stretched status of those polymers melted from the fiber, which is responsible for an instant initiation of the recrystallization at a low temperature. The relevance of our results to the experimental observations of isotactic polypropylene has been discussed.     

Thin fluoropolymer films and nanoparticle coatings from the rapid expansion of supercritical carbon dioxide solutions with electrostatic collection

Application of nanometer thick fluoropolymer films onto metal and semiconducting substrates is described. In the first step, nanometer-sized polymer particles are generated by a process of homogeneous nucleation during the rapid expansion of supercritical fluid solutions. These gas-phase particles are then charged as they are being formed by application of a high voltage to the expansion nozzle. In this way the charged nanoparticles can be collected on a solid surface forming uniform coatings with thicknesses from tens of nanometers to several micrometers thick. Supercritical carbon dioxide solutions of three different fluoropolymers were used to generate different types of coatings. This represents a ‘green’ process for film deposition. A further unique aspect of this process is that the small charged nanoparticles can be deposited to electrically conducting microscopic regions with a spatial resolution better than 50 nm.     

Incorporation of magnetic nanoparticles into lamellar polystyrene-b-poly(n-butyl methacrylate) diblock copolymer films: Influence of the chain end-groups on nanostructuration

In this article, we present new samples of lamellar magnetic nanocomposites based on the self-assembly of a polystyrene-b-poly(n-butyl methacrylate) diblock copolymer synthesized by atom transfer radical polymerization. The polymer films were loaded with magnetic iron oxide nanoparticles covered with polystyrene chains grown by surface initiated-ATRP. The nanostructuration of the pure and magnetically loaded copolymer films on silicon was studied by atomic force microscopy, ellipsometry, neutron reflectivity and contact angle measurement. The present study highlights the strong influence of the copolymer extremity - driven itself by the choice of the ATRP chemical route - on the order of the repetition sequences of the blocks in the multi-lamellar films. In addition, a narrower distribution of the nanoparticles’ sizes was examined as a control parameter of the SI-ATRP reaction.     

The influence of side chains on solubility and photovoltaic performance of dithiophene–thienopyrazine small band gap copolymers

Three small band gap copolymers based on alternating dithiophene and thienopyrazine units were synthesized via Yamamoto coupling and applied in bulk heterojunction solar cells as donor together with PCBM ([6,6]-phenyl C₆₁ butyric acid methyl ester) as acceptor. The polymers have an optical band gap of about 1.3 eV in the solid state and only vary by the chemical nature of the solubilizing side chains. The nature of the side chain has a major effect on solubility and processability of the polymer. Using n-butoxymethyl side chains a soluble, easy to process polymer was obtained that gave the best photovoltaic performance. With short-circuit currents up to 5.2 mA/cm² an efficiency of 0.8% was achieved under estimated standard solar light conditions (AM1.5G, 100 mW/cm²) with spectral response up to 950 nm.     

UV-photopolymerisation of poly(methyl methacrylate)-based inorganic-organic hybrid coatings and bulk samples reinforced with methacrylate-modified zirconium oxocluster

In this work, we developed and optimised a synthetic route which enables to produce by spray-coating hard, transparent and stable inorganic-organic hybrid coatings for a wide variety of different substrates (e.g. stone, stainless steel, polymethylmethacrylate, polyethylene, wood, anodized aluminum). Chemically and thermally stable acrylate-based hybrid materials embedding the zirconium oxocluster Zr₄O₂(OMc)₁₂, OMc(CH₂C(CH₃)C(O)O) were prepared and UV-cured.The coatings of different compositions on different substrates were characterized by numerous analytical and spectroscopic methods such as FT-IR spectroscopy, Angle Resolved-XPS (AR-XPS), Secondary Ion Mass Spectrometry (SIMS), X-ray Absorption Spectroscopy (XAS), Environmental Scanning Electron Microscopy (ESEM) and Energy Dispersive X-ray analysis (EDX). Bulk samples were also prepared for additional characterizations. The bulk samples were analysed by FT-IR, whereas the cross-linking degree was qualitatively evaluated by swelling experiments. As far as the mechanical properties are concerned, the shear storage modulus (G′) and loss modulus (G″) were measured by Dynamical Mechanical Thermal Analysis (DMTA) technique. Moreover, the best conditions for the curing and cross-linking processes of the hybrid materials were studied up to 200 °C by using Differential Scanning Calorimetry (DSC). The thermal stability of the hybrid samples was evaluated by Thermogravimetric Analysis (TGA).     

先进复合材料基体树脂的增韧研究

通过4种聚醚酰亚胺(PEI)PID、PIM、PIP和PIB改性3种热固性树脂(环氧、氰酸酯以及双马来酰亚胺树脂)的研究,讨论了PEI结构、用量、分子质量以及固化剂用量等因素对改性体系的相结构以及力学性能的影响,结果表明控制相结构是增韧基体树脂的关键因素,对基体树脂增韧的研究有指导意义。对不同的热固性树脂体系需采用不同的结构、配方和固化工艺。PIP改性环氧体系呈现的双连续相结构,PEI改性双马来酰亚胺体系,PEI质量分数为5%时呈现了PIM分散粒子相结构,PEI质量分数为10%时呈现了双连续相结构而PEI质量分数大于15%时呈现了相反转结构,PIP分子质量为18 000或20 000时呈现了双连续相结构,而对于PIP改性氰酸酯体系高PIP分子质量较低的呈现双连续相结构,该体系在120℃固化6 h呈现相反转结构,而150℃或180℃固化形成双连续相结构,双连续相结构增韧效果明显。     

Preferential solvation of the eutectic mixture of liquid crystals E7 in a polysiloxane

Blends of the nematic liquid crystal E7 and poly(methylphenylsiloxane) (PMPS) with molecular weight 120,000 g/mol are investigated by high performance liquid chromatography (HPLC) measurements. This study was prompted by observations made recently while analyzing the phase behavior of poly(siloxane)/E7 and poly(acrylate)/E7 systems. A remarkable increase of the nematic to isotropic transition temperature T_NI was found when polymer was added to the liquid crystal. Surprisingly, the increase of T_NI was enhanced with the polymer concentration up to 80 wt%, where it reached its highest value. This behavior could be interpreted by invoking a preferential solvation of the constituents of E7 towards the polymer. The present investigation provides an evidence of this phenomenon using HPLC data.     

Tetrafunctional epoxy resins: Modeling the curing kinetics based on FTIR spectroscopy data

The curing kinetics of two thermosetting systems based on a tetrafunctional epoxy resin was investigated by Fourier transform infrared spectroscopy. Two formulations were studied, in which the hardener was an aromatic diamine and a carboxylic dianhydride, respectively. The quantitative evaluation of the epoxy conversion was based on spectra collected in the near‐infrared range (8000–4000 cm⁻¹) as well as in the medium infrared range (4000–400 cm⁻¹). The kinetic parameters evaluated in the above frequency intervals were significantly different. The reasons for such a discrepancy are discussed critically. Several kinetic models, based on the widely employed Kamal approach, were applied to verify their predictive capability. Satisfactory results were obtained for the amine‐cured system, particularly with a modified equation taking into account the autocatalytic nature of the process as well as a limiting diffusional effect. Less accurate results were achieved for the anhydride‐cured system. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 532–540, 1999     

Infrared spectroscopy of carbonyl species in oxidised diesel distillates

The extent of molar carbonyl group formation in some diesel distillates has been shown, using semiquantitative infrared difference spectroscopy, to differ by about an order of magnitude for three different fuel aging conditions (100 °C/168 h/O₂ atmosphere: 95 °C/16 h/O₂ sparge; ambient storage ≈10⁻³: 10⁻⁴ 10⁻⁵ M). This may partly explain the known unreliability of accelerated oxidation techniques for predicting fuel storage stability. It has also been shown that C=O species present in steam-jet gum residues do not represent those in oxidised fuels prior to evaporation.     

Novel interfacially-polymerized polyamide thin-film composite membranes: Studies on characterization, pervaporation, and positron annihilation spectroscopy

To improve the pervaporation performance of thin-film composite membranes, novel thin-film composite membranes were prepared via interfacial polymerization by reacting 5-nitrobenzene-1,3-dioyl dichloride (NTAC) or 5-tert-butylbenzene-1,3-dioyl dichloride (TBAC) with triethylenetetraamine (TETA) on the surface of a modified polyacrylonitrile (mPAN) membrane (TETA-NTAC/mPAN and TETA-TBAC/mPAN). The effect of the acyl chloride monomers chemical structure on the pervaporation separation of an aqueous ethanol solution was investigated. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, surface roughness and hydrophilicity of the polyamide active layer of the composite membrane. To correlate the variations in the free volume of the polyamide active layers with the pervaporation performance, positron annihilation spectroscopy (PAS) experiments were performed with a variable monoenergetic slow positron beam. From the results of the PAS and XPS experiments, the S parameter, o-Ps annihilation lifetime τ₃ (corresponding to free volume size) and its intensity I₃ (corresponding to free volume concentration), the τ₃ and I₃ of TETA-NTAC polyamide layer (positron incident energy of 1-1.7 keV) were both higher than those of TETA-TBAC polyamide layer. The S parameter for TETA-NTAC polyamide layer was also higher than that of the TETA-TBAC polyamide layer even though the former was more crosslinking than that of the latter. In the aqueous ethanol solution dehydration experiments, the TETA-NTAC/mPAN membrane produced both a higher permeation rate and water concentration in the permeate than the TETA-TBAC/mPAN membrane.     

红外光谱法用于含氟复合膜的膜层厚度研究

在含氟功能膜的研发、生产中,功能膜的厚度控制是最基本、最关键的技术之一.介绍了利用傅里叶变换红外光谱(FTIR)快速测定含氟复合膜中膜层厚度的测试方法.该方法应用在实验室研发中,能够满足研发人员对膜层厚度进行精确定量控制的需求.另外,该方法也可以应用于工业生产,满足生产品控人员对于产品质量及时反馈的需求,保障产品质量的...