In situ real-time monitoring of a diglycidyl ether of bisphenol a epoxy resin modified with poly(etherimide)/polysulphone blends by simultaneous dielectric/near-infrared spectroscopy

Simultaneous dielectric and near infrared measurements were performed in “real-time” to follow polymerisation reactions on blends of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin with 4,4′-diaminodiphenylmethane (DDM) hardener and a mixture of polysulphone (PSU) and polyetherimide (PEI) as modifier. All the blends had a 10 wt% of PSU/PEI mixture. The effect of the PEI/PSU ratio in the mixture was studied. Monitoring of the α-relaxation (related to vitrification) was performed by dielectric measurements, while epoxy conversion was followed by near infrared spectroscopy. The effect of the PEI/PSU ratio on this behaviour was studied, as well as that of the curing temperature. Obtained results were compared with that of the blends with neat PSU and PEI as modifiers.     

Development of Liquid Crystalline Order During Cure of Mesogenic Epoxy Resins

In the present paper we describe the curing process of a new liquid crystalline epoxy monomer with 4,4′-diaminodiphenylenemethane (DDM). The characteristic of cured product is presented. Both the monomer and cured product have been characterized by IR and NMR spectroscopy, differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and dielectric relaxation spectroscopy (DRS).The curing process was analysed with the use of DSC and real-time DRS.     

Molecular dynamics of an epoxy resin modified with an epoxidized poly(styrene-butadiene) linear block copolymer during cure and microphase separation processes

Molecular dynamics of diglycidyl ether of bisphenol A (DGEBA) epoxy resin modified with an epoxidized poly(styrene-b-butadiene) (SepB) linear block copolymer has been monitored during cure and microphase separation process by dielectric relaxation spectroscopy (DRS) for wide frequency and temperature ranges. Different primary and secondary relaxation processes have been analyzed for neat components and ternary mixture. Relaxational behaviour has been modelled with Havriliak-Negami, Vogel-Fulcher-Tammann and Arrhenius equations and fitting parameters and their evolution have been obtained. The retention of the epoxidized poly(butadiene) (PepB) block in the epoxy-rich phase during all the polymerization process, previously detected by our group with atomic force and transmission electron microscopies, has been confirmed by dielectric relaxation spectroscopy. The evolution of molecular dynamics during the polymerization process of the epoxy resin in the ternary system indicates a change in the trend of the main relaxation at times that agree with phase separation detected by rheology.     

Effect of curing on the broadband dielectric spectroscopy of powder coating

The effect of curing process of thermosetting powder coating consists of carboxylated polyester resin cured with triglycidyl isocyanurate has been investigated using broadband dielectric relaxation spectroscopy over a wide range of frequency (10⁻¹-10⁶ Hz) and temperature (70-105 °C) for different constant curing times. The molecular dynamics of the glass relaxation process (α-process) was investigated as a function of curing time, frequency, and temperature. It has been found that, only one common α-relaxation process has been observed for all measured samples of different degree of curing stages, its dynamics and broadness were found to be curing time dependent. In addition, the curing time dependence of the dielectric relaxation strength, Δε, has also been examined for the α and β-relaxation processes. The Δε for the two relaxation processes decreased strongly at the beginning of curing process and then became almost constant at longer curing times. This finding implied that the numbers of reoriented dipoles decrease with curing time as a result of the formation of three-dimensional polymer network. Furthermore, the dislocation energy, ε_s, calculated from the Meander model was found to be increased with increasing the curing time, i.e. the formation of a three-dimensional polymer network produces many structural defects or dislocation points. In addition, the activation energy of the curing process was calculated from the analysis of the calorimetric exothermic peaks of the curing process at different heating rates.     

Phase separation in a poly(ether sulfone) modified epoxy-amine system studied by temperature modulated differential scanning calorimetry and dielectric relaxation spectroscopy

The phase separation induced by the curing reaction of an epoxy based on diglycidylether of bisphenol A (DGEBA) with methylene dianiline (MDA) modified with poly(ether sulfone) (PES) at a concentration of 20 wt% was studied by temperature modulated differential scanning calorimetry (TMDSC) and dielectric relaxation spectroscopy (DRS). The effect of phase separation on the curing kinetics and vitrification phenomena is analysed. The dependence of the log of the measuring frequency on the degree of conversion allows the correlation between the dipolar relaxation of each phase and the vitrification observed by TMDSC to be established.     

Epoxy resins and epoxy blends studied by near infra-red spectroscopy

The cure and the final network of epoxy resins have been investigated by numerous techniques, nevertheless a clear understanding of this network structure has not yet been achieved. FTIR analysis of polymeric materials provides highly precise measurements that are widely interpretable in terms of chemical structure. Yet the high absorption of fundamental bands requires careful sample preparation to reduce the thickness of the sample or special reflection techniques are needed. Furthermore, the occurrence of overlapping bands for epoxy resin (N-H and O-H vibrations in the 3000 cm⁻¹ region) renders the quantitative analysis in the region mid IR particularly difficult. However, the overtone and combination bands are 10–100 times weaker than the fundamental ones and are observed in near infrared (NIR) region. Longer pathlengths than Mid IR ones can be used allowing transmission analysis of thick samples (1-20 mm) without special preparation. NIR absorption bands have different intensities depending on the anharmonicity of vibrations. The strongest absorption bands are due to protons connected to carbon, nitrogen, oxygen. Hydrogen bonding due to inter- and intramolecular interactions can cause band broadening, peak position shifts and intensity variations. NIR spectroscopy is therefore a useful technique to investigate polymeric materials and was used to study the cure reactions of various epoxy resins cured with amine hardener. Using different NIR techniques (reflectance, transmission and microscopy) we will briefly present some results concerning hydrogen bonding between epoxy and amine hardener before curing, epoxy resins, glass/epoxy composites and epoxy/PES (polyethersulfone) blends.     

Amphiphilic block copolymers based on poly(2-acryloyloxyethyl phosphorylcholine) prepared via RAFT polymerisation as biocompatible nanocontainers

Amphiphilic block copolymers composed of poly(butyl acrylate) and poly(2-acryloyloxyethyl phosphorylcholine) have been prepared using reversible addition fragmentation transfer (RAFT) polymerisation. The conversion of the polymerisation was determined using online FT NIR spectroscopy. NMR spectroscopy was used not only to support the results obtained from FT NIR spectroscopy but also prove the formation of micelles. Due to the strong aggregation tendency of these block copolymers and the resulting difficulties concerning the molecular weight analysis test experiments were carried out replacing poly(2-acryloyloxyethyl phosphorylcholine) with poly(2-hydroxyethyl acrylate). Micelle size and the aggregation behaviour were investigated using dynamic light scattering. The sizes of the nanocontainers obtained were found to be influenced by the block length as well as the solvent leading to micelles in the range between 40 and 160 nm. The toxicity of the RAFT agent used was then analysed by cell growth inhibition tests.     

Bulk radical homo-polymerisation studies of commercial acrylate monomers using near infrared Fourier transform Raman spectroscopy

In our previous work we have used near infrared Fourier transform Raman spectroscopy to provide a reliable, reproducible and quantitative method for in situ reaction monitoring of homo-polymerisation. Model systems such as styrene and methylmethacrylate were studied. In this present work three commercial monomers have been studied, namely butylacrylate, hydroxylpropylmethacrylate and laurylmethacrylate. The effects of reaction temperature, monomer additives and the presence of oxygen have been elucidated. These reaction variables have been shown to have a significant effect on polymerisation rate in particular for the butylacrylate system.     

Spectroscopic probes for real-time monitoring of polymer modification and degradation reactions

The processing of polymers may be accompanied by oxidation and elimination reactions that affect the quality of the final product. In reactive processing, polymerisation occurs in the extruder or autoclave and the extent of reaction becomes an important process variable. The monitoring of these chemical changes in real-time so that processing may be optimised requires the use of analytical methods such as fibre-optic Near Infrared (NIR) spectroscopy. In this paper the requirements and limitations for this and related spectroscopic probes are described and novel approaches based on infrared emission and transient infrared transmission spectroscopy (TIRTS) are discussed. To cite this article: G. George et al., C. R. Chimie 9 (2006).     

Application of near infrared spectroscopy and multivariate data analysis for the evaluation of glue lines of untreated and copper azole treated laminated timber before and after ageing

The necessity for inspection and assessment of glued laminated timber structures in service has raised interest in the evaluation of the glue lines. Glue line spectra were analysed and are discussed in detail with respect to spectral contributions from the adhesive, the hardener, the wood lamella below the adhesive, the curing temperature as well as ageing-related spectral changes. The combination of near infrared (NIR) spectroscopy and principal component analysis (PCA) allowed distinguishing between aged and non-aged samples and different copper azole preservative treatment levels of phenol-resorcinol-formaldehyde (PRF) glue lines. NIR-based partial least squares (PLS) regression modelling was performed for the glue line shear strength and for the curing temperature. These findings show that NIR spectroscopy is a fast and useful technique to evaluate the degradation on the PRF glue lines of untreated and copper azole treated laminated timber.     

Dielectric relaxations in PEEK by combined dynamic dielectric spectroscopy and thermally stimulated current

The molecular dynamics of a quenched poly(ether ether ketone) (PEEK) was studied over a broad frequency range from 10^?3 to 10⁶ Hz by combining dynamic dielectric spectroscopy (DDS) and thermo-stimulated current (TSC) analysis. The dielectric relaxation losses ε′′_KK has been determined from the real part ε′_T(ω) thanks to Kramers–Kronig transform. In this way, conduction and relaxation processes can be analyzed independently. Two secondary dipolar relaxations, the γ and the β modes, corresponding to non-cooperative localized molecular mobility have been pointed out. The main α relaxation appeared close to the glass transition temperature as determined by DSC; it has been attributed to the delocalized cooperative mobility of the free amorphous phase. The relaxation times of dielectric relaxations determined with TSC at low frequency converge with relaxation times extracted from DDS at high frequency. This correlation emphasized continuity of mobility kinetics between vitreous and liquid state. The dielectric spectroscopy exhibits the α_c relaxation, near 443 K, which has been associated with the rigid amorphous phase confined by crystallites. This present experiment demonstrates coherence of the dynamics of the PEEK heterogeneous amorphous phase between glassy and liquid state and significantly improve the knowledge of molecular/dynamic structure relationships.     

Beyond the first hydration shell: dielectric study of LiCl aqueous solution

The dielectric constant for lithium chloride (LiCl) in aqueous solution with the entire concentration has been determined in the frequency range 0.5 GHz–50GHz at 298 K by dielectric relaxation spectroscopy (DRS). The system behaviour is described according to the Cole–Cole and two Debye-type relaxation functions whose evolution with composition is analysed. Combining the Cole–Cole and two Debye-type relaxation functions, the results of the dielectric properties of aqueous LiCl solution are presented and discussed. The maximum number of water molecules perturbed by ions in the hydration shell decays with its concentration. Using the extended Froehlich theory, it is concluded that the water structure is perturbed by ions beyond the first hydration shell in LiCl aqueous solution system.     

Photon correlation spectroscopy of polystyrene near the glass–rubber relaxation

Polarized Rayleigh scattering is studied near the glass-rubber relaxation in atactic polystyrene using photon correlation spectroscopy. Average relaxation times determined from the data agree well with previous results obtained using depolarized Rayleigh scattering. The light scattering results follow the same trend observed by dielectric and mechanical relaxation studies, but the times for orientational relaxation are longer by approximately two orders of magnitude. Also, an extensive discussion of the experimental techniques necessary to use photon correlation spectroscopy of polymers near the glass-rubber relaxation is presented.     

Effects of different composition ratio on the dielectric relaxation and dynamic mechanical properties of poly(ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers

The molecular dynamics of new poly (ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers (DL/CL/PAC) has been investigated by using dynamic mechanical thermal analysis (DMTA) and dielectric relaxation spectroscopy (DRS) measurements. The copolymers were synthesized via anionic polymerization of relevant lactams activated with carbamoyl derivatives of telechelic hydroxyl terminated polypropylene oxide with isophorone diisocyanate (PAC). The calorimetric, X‐ray diffraction, and DMTA measurements were performed to recognize the influence of the composition ratio and the type of PAC on the physical, thermal, and mechanical properties of the synthesized copolymers. The DRS was used to study the frequency dependence of the dielectric permittivity of some isotherms from ?110 to 145 °C. Copolymerization of ε‐caprolactam with about 10 wt % ω‐dodecalactam results in a copolymer that has lower water absorption, a melting point close to that of polyamide 6 and has a high enough degree of crystallinity in respect to high storage modulus. Five dielectric relaxations have been observed in the dielectric spectra, three at lower temperature and two at higher temperature. The copolymers have two glass transition temperatures for polyamide segments and polyether blocks, indicating microphase separation in the copolymers. Other studies directed toward molecular dynamics of polyamide DL/CL/PAC copolymers have not been reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

金红石相TiO2纳米棒的氢化处理及其光催化活性

以钛酸四丁酯为钛源,通过盐酸调制的水热法制备出了具有棒状结构的金红石相纳米TiO₂,并进一步进行高温氢化处理. 采用X射线衍射（XRD）,透射电镜（TEM）,紫外-可见-近红外漫反射（UV-Vis-NIR DRS）,电子顺磁共振（EPR）和表面光伏（SPS）等测试手段对样品进行表征,以气相乙醛和液相苯酚为目标污染物考察催化剂的光催化活性. 结果表明：随着高温氢化处理时间的延长,TiO₂样品的可见光吸收逐渐增强,其颜色逐渐由白色转变成灰色,这主要与引入的Ti³⁺/氧空位缺陷有关. 表面光电压谱和羟基自由基测试表明,适当时间的氢化处理有利于光生电荷的分离. 在光催化氧化降解气相乙醛和液相苯酚过程中,经适当时间氢化处理的样品表现出高的可见光催化活性. 并且可见光催化活性的规律与紫外光下的是一致的. 这是因为氢化处理后在导带底下方引入了缺陷能级,拓展了可见光响应. 过度的氢化处理会在TiO₂导带下方引入较低的缺陷能级,使光生电荷的复合加剧,导致光催化活性降低.     

Discrimination of Ephedra plants with diffuse reflectance FT-NIRS and multivariate analysis

The secondary metabolites of different Ephedra plants are various. Therefore, the discrimination of different Ephedra plants is significant. An objective, easy-to-use, rapid and pollution-free approach is proposed for discriminating Ephedra plants of different species, habitats and picking times on the basis of diffuse reflectance Fourier transform near infrared spectroscopy (FT-NIRS) measurements and multivariate analysis. The Fourier transform near infrared diffuse reflectance spectra (NIRDRS) were acquired from 37 pulverized samples of Ephedra plants put in glass vials in the near infrared (NIR) region between 10 000 and 4000 cm⁻¹, averaging 64 scans per spectrum at a resolution of 4 cm⁻¹. After spectra processing and data pre-processing, spectral data were analyzed respectively with three multivariate analysis techniques: discriminant analysis (DA), self-organizing map (SOM) and back-propagation artificial neural network (BP-ANN). The proposed method could distinguish not only the Ephedra plants of three species and two habitats but also the plants picked at different times of day without special sample treatment and the use of chemical reagents. The performance indexes of the DA model were 84.2-91.9% and the prediction accuracies of both the SOM and the BP-ANN models reached 93.3-100.0%.     

A dielectric study of molecular relaxations in irradiated high density polyethylene

The molecular relaxation behaviour of high density polyethylene (HDPE), exposed to gamma radiation in air to various absorbed doses (up to 700 kGy), has been investigated by dielectric loss (tanδ) analysis. All relaxation zones (γ, β and α, in order of increasing temperature), between 25 K and the melt temperature, were studied in the frequency range from 1 kHz to 1 MHz. The changes observed in the dielectric relaxation spectra were related to the modifications in the structural and morphological parameters attributed to exposure of the samples to radiation. Radiation-induced changes in the crystal fraction, oxidative degradation and degree of network formation, observed by wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), infrared spectroscopy (IR) and gel measurements, were well connected with the changes in intensity, position and activation energy of α and γ relaxations. Complete disappearance of the already weak β relaxation with irradiation is attributed to the more restricted chain segment mobility in the net structure, but the contribution due to radiation-induced increase in crystallinity should also be taken into account.     

阴离子表面活性剂SDBS胶束溶液的介电弛豫行为

用射频介电谱方法研究了0.1-80 mmol·L-1浓度的十二烷基苯磺酸钠(SDBS)水溶液体系的介质弛豫行为. 测量发现频率接近107 Hz时, 在临界胶束浓度(CMC)附近出现显著的介电弛豫现象. 采用Cole-Cole函数拟合SDBS体系介电数据, 其拟合参数具有明显变化规律: 介电增量(△ε)随SDBS摩尔浓度(cs)的增加而增大, 表现为两种线性关系, 并在cs=36 mmol·L-1附近出现拐点; 特征弛豫时间(τ0)却在cs=45 mmol·L-1出现极小值. 利用胶束电模型分析了介电弛豫机制, 认为束缚Na+对离子数量和胶束体积变化是引起介电增量和特征弛豫时间变化的两个重要原因.     

Gel production, oxidative degradation and dielectric properties of isotactic polypropylene irradiated under various atmospheres

In this work, changes in structure and physical properties of stabilized isotactic polypropylene (iPP) were created by gamma irradiation, up to a dose of 700 kGy, in different media: air, deionised distilled (DD) water and acetylene. Gel and infrared (IR) spectroscopy measurements were used to determine the changes in the degree of network formation and oxidative degradation, respectively. Sol-gel analysis was studied in detail using the Charlesby-Pinner (C-P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan δ) analysis in a wide temperature and/or frequency range. Evolution of low temperature dielectric relaxations with gamma irradiation was investigated. In the case of dielectric relaxation measurements, the polar groups that were introduced by irradiation in non-polar iPP were considered as tracer groups. Conclusions derived according to different methods were compared.