Effects of X-ray radiation on the surface chemical composition of plasma deposited thin fluorocarbon films

Different thin fluorocarbon (FC) films were deposited on Si(111) using plasma polymerisation and then exposed to X-ray radiation. Changes in the chemical composition of the deposited fluorocarbon films as a function of irradiation time were investigated in situ using X-ray photoelectron spectroscopy. The evaluation of the C1s and F1s core level induced emission as a function of exposure to X-ray radiation (Mg Kα, hν = 1253.6 eV) reveals changes in the surface chemical composition of the FC polymer structure. The presented results indicate a high defluorination under X-ray irradiation. Additionally, binding energy shifts of the F1s and C1s peaks during the exposure associated with surface charging effects were observed. With ongoing exposure the surface charging decreases continuously and the FC surfaces become more conductive due to changes in the polymer structure. Different models have been used to describe the decomposition kinetics and surface composition.     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

Thermal stability and degradation products analysis of benzocyclobutene-terminated imide polymers

Benzocyclobutene-terminated imides were prepared and fully characterized with ¹H NMR, MS, and FT-IR. The thermal degradation of polymers was investigated by using thermogravimetric analyzer (TGA) and high-resolution pyrolysis-gas chromatography–mass spectrometry (HR-Py-GC–MS). TGA showed that thermal degradation of the polymer was a single-stage process in N₂, whereas a three-stage degradation in air atmosphere. The major involved products were found to be CO₂, naphthalene and naphthalene derivatives. Degradation mechanism of the polymer was suggested and the relationship between structures of the polymer and degradation products was also discussed.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Thermal effect on microstructure vibration of SiO2 thin films

The microstructure of amorphous SiO₂ thin film is a random network structure in which a large amount of [SiO₄] is interconnected with a specific SiOSi bond angle. The SiO₂ thin films used in this paper were prepared by ion beam sputtering and electron beam evaporation deposition techniques. Two-dimensional correlation spectroscopy analysis techniques were used in this study. By measuring the infrared temperature spectrum, we obtained the two-dimensional correlation synchronous spectrum and asynchronous spectrum, and decomposed the in-phase and out-phase asymmetric stretching vibration characteristics of SiOSi. As the temperature increases, the spectral transmittance of the vibrating peak decreases, and the relative change of in-phase asymmetric stretching vibration absorption peak is higher than that of the out-phase asymmetric stretching vibration absorption peak.     

Effect of annealing on hydrophobic stability of plasma deposited fluoropolymer coatings

Fluorinated amorphous carbon (a-C:F) films e.g. plasma polymerised perfluorocyclobutane have long attracted much consideration due to their low surface energy, hydrophobicity, low refractive index, good electrical and thermal insulation and good thermal stability. Although a-C:F films have many advantages, hydrophobic stability over time in air and water remains a major concern. In this study, the effects of weathering conditions on the hydrophobicity of fluorocarbon films prepared from perfluorocyclobutane precursors were examined using water contact angle measurements. It was found that the high initial hydrophobicity of as-deposited films degrades rapidly in humid conditions. The stability of hydrophobicity can be significantly improved when a suitable treatment such as annealing is employed. The mechanism of weathering was explained with the help of a number of morphological and chemical characterisation techniques such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). In particular, XPS results demonstrated that a reduction in the overall amount of -CF₃ radical, oxygenation of surface fluorides and the formation of an overlayer all influence the degradation of fluorocarbon in aquatic environment.     

Thermal stability and dehydration of anapaite

The thermal behavior of anapaite, Ca₂Fe²⁺(PO₄)₂·4H₂O, has been studied by TG/DTG and DSC techniques, complemented by Fourier-transform IR spectroscopy. The anapaite sample, originating from Bellaver de Cerdena (Spain) was identified as such using X-ray diffraction and qualitative energy-dispersive analysis of X-rays. ⁵⁷Fe Mössbauer spectroscopy at various temperatures could not detect any Fe³⁺. It was found from thermal analyses and IR spectroscopy that two types of hydrogen–bonded water molecules exist in the structure. This feature is related to the distance between the hydrogen atom of a water molecule and the oxygen atom of a phosphate group, the distance between both oxygen atoms and the angle O(H₂O)–HO(PO₄). The dehydration process proceeds in two partially overlapping steps. The removal of the last two, strongly bonded water molecules is accompanied by the decomposition of the crystal structure. From TG curves, the activation energy was calculated for different intervals of dehydration reaction. For this purpose, five slow heating rates between 0.4 and 2°C/min were applied. The activation energy for the entire process was also obtained from DSC (223 kJ/mol) and found to be in reasonable agreement with the average of the various values from the TGA (233 kJ/mol). The heat of reaction for the complete dehydration was found to be 177 kJ/mol.     

聚氨酯的热分解研究进展

介绍了有关聚氨酯热性能研究的状况,着重阐述了聚氨酯在不同气氛下的热解机理及热解动力学的内容,同时也阐述了聚氨酯今后热解研究的发展方向。     

Thermal behaviour of polyacrylamidoxime-copper chelates

The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime-copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.     

Thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers in inert atmosphere

The thermal stability of poly(N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves suggested that the effective degradation of both systems occurred in the temperature range 350–500 °C with more than 60% mass loss. At this temperature, the activation energy was in the range 160–200 kJ mol⁻¹ (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO₂, CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH₃ which was apparently suppressed in the copolymer by the formation of large amounts of CO₂ and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.     

Thermal and structural stability of composite systems based on polyaniline deposited on porous polyethylene films

Conducting composite systems containing polyaniline layers produced on the surface and inside the pores of polyethylene support have been prepared. Microporous polyethylene films were obtained by melt extrusion with subsequent annealing, uniaxial extension, and thermal fixation. Polyaniline layers were formed by in-situ polymerization of aniline onto polyethylene porous support placed into the aqueous reaction mixture. Structural and chemical transformations upon heating of these systems in air in free state and in vacuum under load have been investigated by thermo-mechanical tests, IR spectrometry, and electron microscopy. Changes in mechanical properties of composites after heating have been analyzed. Composite systems have been found to demonstrate a considerably lower shrinkage upon heating than microporous polyethylene substrates. It has been discovered that the composites preserve mechanical integrity on heating up to temperatures much higher than the polyethylene melting point. It is concluded that thermo-mechanical behaviour of the composites is determined by the space-continuous phase of polyaniline on the surface and in the bulk of polyethylene support.     

Thermal stability and flame-retardancy mechanism of poly(ethylene terephthalate)/boehmite nanocomposites

The thermal stability and flame-retardancy properties of poly(ethylene terephthalate)/nano-boehmite composites (PET/AlOOH) were investigated using composites prepared in situ. Combustion behaviour and flammability were assessed using the limiting oxygen index (LOI) and cone calorimetry. The incorporation of nano-boehmite increased the LOI of PET from 18 to greater than 25. Cone calorimetry showed that the heat release rates and total smoke production values of PET/AlOOH composites were significantly less than those of pure PET. It also showed that PET/AlOOH combustion produced greater quantities of char residues than did PET combustion. These results showed that nano-boehmite is an effective flame-retardant for PET. Combustion residues were examined using scanning electron microscopy, indicating that nano-boehmite addition produced consistent, thick char crusts. Thermal stability and pyrolysis were investigated using thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry, showing that thermal stability of PET/AlOOH was superior to that of pure PET, fewer cracking products were produced in nanocomposite combustion than in pure PET combustion, and pyrolysis of the flame-retardant polyester was incomplete. We propose a condensed phase mechanism for the PET/AlOOH flame-retardancy effect.     

Determination of fluoxetine in plasma by gas chromatography-mass spectrometry using stir bar sorptive extraction

This article presents a method employing stir bar sorptive extraction (SBSE) with in situ derivatization, in combination with either thermal or liquid desorption on-line coupled to gas chromatography-mass spectrometry for the analysis of fluoxetine in plasma samples. Ethyl chloroformate was employed as derivatizing agent producing symmetrical peaks. Parameters such as solvent polarity, time for analyte desorption, and extraction time, were evaluated. During the validation process, the developed method presented specificity, linearity (R² > 0.99), precision (R.S.D. < 15%), and limits of quantification (LOQ) of 30 and 1.37 pg mL⁻¹, when liquid and thermal desorption were employed, respectively. This simple and highly sensitive method showed to be adequate for the measurement of fluoxetine in typical and trace concentration levels.     

Thermal decomposition and stability in a series of tetrafluorborate copper(I) complexes

Tetrafluorborate copper(I) complexes containing acetonitrile, triphenylphosphine, 1,10-phenanthroline,2,2′-bipyridine and 2-quinolinethiol have been prepared in order to study their thermal stabilities as a function of the ligands present. The characterization of the above compounds was carried out by elemental analysis and IR spectroscopy. Their thermal behaviour has been investigated and the final products were identified by X-ray powder diagrams.     

Synthesis,Characterization, Thermal Property of Si(c‐C5H9NH)4 and Its Potential as CVD Precursor for SiC Film

Silicon(IV) amide Si(c‐C₅H₉NH)₄ ( 1 ), was synthesized and characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy, EI‐MS, elemental analysis, and X‐ray diffraction. Its thermal stability and volatility were also investigated. The as‐grown film, which was characterized by SEM, AFM, XRD and XPS, was deposited using 1 as single precursor through a low‐pressure chemical vapor deposition (LPCVD) process at a temperature as low as 600 °C. The results demonstrated that silicon(IV) amides can be promising single‐precursor for deposition of low‐temperature SiC films.     

CH3（ad）在清洁及预吸附氧Pd（100）表面的热脱附性能

用高分辨电子能量损失谱，热脱附谱，紫外光电子能谱研究了ＣＨ３在清洁及预吸附氧Ｐｄ表面上的热稳定性。ＣＨ３由ＣＨ３Ｉ在Ｐｄ表面的热分解来产生。ＣＨ３Ｉ的ＨＲＥＥＬＳ表明，ＣＨ３中的Ｃ－Ｈ键近似与表面平行，ＣＨ３Ｉ在Ｐｄ表面低于１１０Ｋ时已裂解为ＣＨ３和Ｉ，大量的ＣＨ３在２００－２１０Ｋ的温度范围内的Ｈ结合并以ＣＨ４的形式脱附，但在氧改性表面，ＣＨ４脱附的温度范围变宽，脱附温度有所提高，可能是由于表面     

Thermal degradation and stability of epoxy nanocomposites: Influence of montmorillonite content and cure temperature

The thermal behaviour and stability of epoxy nanocomposites were studied by thermogravimetric analysis (TGA). The nanocomposites consisted of a trifunctional epoxy resin, a hardener containing reactive primary amine groups and clay nanoparticles (i.e. montmorillonite), previously treated with octadecyl ammonium. Three levels of nanoclay content (0, 5 and 10%) and three temperature levels (120, 150 and 200 °C) were used. The exfoliation of nanoparticles within the material was analyzed by X-ray diffraction (XRD). The cure conversion was determined by Fourier transform infrared (FTIR) spectroscopy by selecting the suitable band for epoxide functional groups. The study demonstrated that the nanoclay greatly accelerates the cure, at the different cure temperatures studied. Finally, the thermal stability of the various nanocomposites was established by calculating various characteristic temperatures from thermograms as well as conversion and conversion derivative at maximum decomposition rate. The collisions between resin molecules, which are trapped within the nanoclay galleries, were less effective because they were protected against thermal degradation by the galleries. However, once the collision was effective, the thermal activation occurred more readily.     

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L⁻¹ NaClO₄) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD-MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25-800 °C range, with focus on thermal/chemical processes up to 250 °C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40-110 °C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV-vis absorption spectroscopy after storage at temperatures up to 95 °C, and storage times up to 1 week. For temperatures below 100 °C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 °C this process was totally reversible. Above 70 °C an irreversible loss of water was also observed, which according to UV-vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 °C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 °C), gradual decomposition resulting in the formation of carbon dioxide (110-240 °C), and carbon monoxide (140-240 °C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 °C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material.     

Silver sulfide/poly(3-hydroxybutyrate) nanocomposites: Thermal stability and kinetic analysis of thermal degradation

The non-isothermal degradation of poly(3-hydroxybutyrate) (PHB) and silver sulfide/poly(3-hydroxybutyrate) (Ag₂S/PHB) nanocomposites was investigated using thermogravimetric (TG) analysis. In the composite materials, Ag₂S caused the degradation of PHB at a lower temperature as opposed to that of neat PHB. Moreover, an increase Ag₂S loading in the PHB decreased the onset temperature (T_onset) of thermal degradation, whereas it was raised upon augmenting the heating rate. From Kissinger plots, the observed trend of the degradation activation energy, E_d, was attributed to polymer-particle surface interactions and the agglomeration of Ag₂S. The thermal degradation rate constant, k, was linearly related to the Ag₂S loading in PHB. Thus, the Ag₂S nanoparticles effectively catalyzed the thermal degradation of PHB in the Ag₂S/PHB nanocomposites. Differential scanning calorimetry (DSC) data also supported the catalytic property of Ag₂S.     

Thermal stability of polyurethanes

Summary The combined application of thermogravimetry reactiongas chromatography and gel-permeation chromatography permits to follow the heat degradation of polyurethane polymers in inert gas, air and water-saturated environment. The examinations give information on the rate of thermal degradation, the individual volatile degradation components, the critical points of the polymer chains and on the change of their molecular-weight distribution. Gas chromatographic examinations also permit the identification of the chain-extending components of different types of polyurethanes.