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.     

Positron annihilation lifetime spectroscopy of molecularly imprinted hydroxyethyl methacrylate based polymers

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) (HEMA) matrix was achieved to create three-dimensional cavities to recognize and bind glucose. Molecularly imprinted polymers (MIPs) were synthesized with different types of crosslinkers and varying amounts of template molecule in an attempt to elucidate the impact of imprint quantities on the effectiveness of imprinting technique. The crosslinking agents used in this study were diethylene glycol diacrylate (DEGDA), triethylene glycol dimethacrylate (TEGDMA) and polypropylene glycol dimethacrylate (PPGDMA) in the order of increasing chain length. Crosslinking agent concentration in the polymerization mixture (monomer, crosslinking agent and template) covered a range of 10, 20, 30, and 70 mol%. The mole ratio of template molecule, d-glucose to functional monomer, HEMA, was kept either as 1:3 or 1:6. The absorbed dose varied from 1 to 15 kGy. Control polymers were synthesized with exactly the same composition in the absence of d-glucose. Cavity sizes of MIPs were investigated by positron annihilation lifetime (PAL) measurements. A sandwich arrangement (sample-source-sample) was used. PAL experiments were carried out using a conventional fast-fast coincidence system having a time resolution (FWHM) of about 280 ps. Free-volume hole radii of samples were investigated in their dry and fully water swollen state.The results obtained from a systematic study of the effects of concentration and molecular size of the crosslinking agents, template to monomer ratio and irradiation dose experiments suggest that control of cavity size is feasible in nanometer scale by the optimization of these parameters revealed by means of (PAL) spectroscopy technique.     

Study of the distribution of the molecular orientation in thick polyethylene samples by X-ray diffraction, infra-red dichroism and Raman spectroscopy

The molecular orientation in thick polyethylene samples has been studied by wide-angle X-ray diffraction, i.r. dichroism and Raman spectroscopy. The original specimens, with dimensions of the order of a centimetre, were cut to obtain 1 mm thick platelets on which the measurements were made. The mean coefficient of the second-order Legendre polynomial, P₂, was calculated from X-ray diffraction and from the 1894 cm⁻¹ i.r. band for the crystalline phase, from the 909 cm⁻¹ i.r. band for the vinyl end groups and from the 1130 and 1060 cm⁻¹ Raman bands for the all-trans C-C conformers. The fourth-order coefficient, P₄, was also determined from X-ray diffraction and Raman spectroscopy for a series of cylindrical rods of draw ratios (λ) ranging from 6 to 20. An excellent correlation is observed between the P₂ coefficients measured from different X-ray reflections and from the 1894 cm⁻¹ i.r. band. The Raman spectroscopy results show that the all-trans bonds located in the amorphous phase are aligned perpendicular to the extrusion direction for the λ = 6 rod, and gradually reorient towards the fibre axis for λ values up to 20, while the P₂ and P₄ coefficients calculated for the crystalline phase remain constant at λ ≥ 12. The variation of the orientation through the thickness of the samples was investigated for the cylindrical rods and for an H-shaped moulding produced by extrusion and rolling. Minor differences in the degree of molecular orientation were detected between the centre and the surface of the rods, whereas important variations were measured for the H-shaped sample.     

X-ray absorption fine structure spectroscopy and X-ray diffraction study of cementitious materials derived from coal combustion by-products

Cementitious materials derived from coal combustion by-products have been investigated by means of X-ray diffraction (XRD) and S and Ca K-edge X-ray absorption fine structure (XAFS) spectroscopy. The XRD analysis revealed that these materials are a complex mixture of a small amount of quartz [SiO₂] and three calcium-bearing compounds: hannebachite [CaSO₃·1/2H₂O], gypsum [CaSO₄·2H₂O] and ettringite [(Ca₆(Al(OH)₆)₂(SO₄)₃·26H₂O)]. Analysis of the S XAFS data focused on deconvolution of the X-ray absorption near-edge structure (XANES) regions of the spectra. This analysis established that sulfate and sulfite are the two major sulfur forms, with a minor thiophenic component contained in unburned carbon in the fly ash. Increasing sulfate and decreasing sulfite correlated well with increasing gypsum and ettringite and decreasing hannebachite content in the samples. Different calcium compounds were identified primarily through simple comparison of the Ca K-edge XANES and radial structure functions (RSFs) of the cementitious samples with those of reference compounds. Because of the complex coordination chemistry of calcium in these materials, it was difficult to obtain detailed local atomic environment information around calcium beyond the first CaO peak. Analysis of the extended X-ray absorption fine structure (EXAFS) and the RSF gave average CaO distances in the range 2.44-2.5 Å, with each calcium atom surrounded roughly by eight oxygen atoms. In certain samples, the average CaO distances were close to that in ettringite (2.51 Å), suggesting that these samples have higher ettringite content. The results of S and Ca K-edges XAFS and the XRD data were in reasonable agreement.     

The application of multiscale quasi 4D CT to the study of SrCrO4 distributions and the development of porous networks in epoxy-based primer coatings

Transport paths for inhibitor release within a model strontium chromate (SrCrO₄) inhibited/epoxy primer have been studied using a combination of tomography techniques. It has been found that the SrCrO₄ particles form independent clusters within the model primer. The clusters have a range of fractal dimensions with the largest clusters (a few hundred microns in size) having a fractal dimension of 2.36. Leaching of the SrCrO₄ from the primer appears to be initially through direct dissolution of particles in contact with the electrolyte but changes to diffusion through void pathways created by dissolution of the SrCrO₄ phase. No evidence was found for the diffusion of chromate ions through the epoxy. Transport through such clusters does not follow Fickian diffusion, which has traditionally been employed to describe inhibitor release dynamics. Release kinetics typically follow a t^m behaviour where t is time and m is an index which would be 0.5 for Fickian diffusion. Thus the overall release with time will evolve, being initially the result of direct dissolution, then at intermediate times, be dominated by transport through the fractal network and at the final stage go to zero since all the strontium chromate will be dissolved from the cluster connected to the surface. Clusters not connected to the surface remain undissolved and form additional reservoirs for further release in when local damage occurs in their vicinity. This new model of inhibitor transport creates new strategies for the development of self-healing properties for coatings.     

Analysis of the cure reaction of carbon nanotubes/epoxy resin composites through thermal analysis and Raman spectroscopy

The effect of the incorporation of single‐walled carbon nanotubes (SWNTs) onto a diglycidyl ether of bisphenol A‐based (DGEBA) epoxy resin cure reaction was investigated by thermal analysis and Raman spectroscopy. The results of the investigation show that SWNTs act as a strong catalyst. A shift of the exothermic reaction peak to lower temperatures is, in fact, observed in the presence of SWNTs. Moreover, these effects are already noticeable at the lowest SWNT content investigated (5%) with slight further effects at higher concentrations, suggesting a saturation of the catalyzing action at the higher concentrations studied. The curves obtained under isothermal conditions confirm the results obtained in nonisothermal tests showing that the cure reaction takes less time with respect to the neat epoxy. The thermal degradation of cured DGEBA and DGEBA/SWNT composites was examined by thermogravimetry, showing a faster thermal degradation for DGEBA–SWNT composites. Raman spectroscopy was successfully applied to demonstrate that the observed changes in the cure reaction of the composites lead to a different residual strain on the SWNT bundles following a different intercalation of the epoxy matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 452–458, 2003     

Identification of inductive behavior for polyaniline via electrochemical impedance spectroscopy

Polyaniline (PANI) film electrodeposited in HCl medium using cyclic voltammetry (CV) with an upper potential limit of 0.90 V, exhibited an inductive behavior. PANI films deposited with different conditions were subjected to various applied potentials and the impedance characteristics were recorded through electrochemical impedance spectroscopy (EIS). The impedance results clearly reveal the existence of inductive behavior to PANI. Inductive behavior was observed for PANI films deposited with conditions which favor benzoquinone/hydroquinone (BQ/HQ) formation and further evidenced by X-ray photoelectron spectroscopy (XPS). A comparative analysis of the EIS and XPS results of PANI films prepared under similar conditions with the upper potential limits of 0.75 and 0.90 V, respectively, clearly documented that the presence of BQ/HQ, the degradation product of PANI, formed during the electrochemical polymerization at the upper potential limits causes inductive behavior to PANI.     

Quantitative characterization of orientation in PET fibres by Raman spectroscopy

Attempts to obtain quantitative measures of orientation on fibres of diameter ～ 10μm by the method used earlier on films were unsuccessful. This is believed to be due to polarization scrambling caused by reflection and refraction at the surface of the fibre. It is shown that by immersing the fibres in a liquid of refractive index equal to the mean of those of the fibre the method can be used successfully.     

Wide-angle X-ray scattering,Fourier transform infrared spectroscopy,and scanning electron microscopy studies on the influence of the addition of liquid functional rubber into epoxy thermoset

Sophisticated analytical methods (viz. wide-angle X-ray scattering, Fourier transform infrared spectroscopy, and scanning electron microscopy have been applied to investigate the mechanism of toughening of epoxy cresol novolac resin due to the addition of carboxy-terminated polybutadiene (CTPB) liquid functional rubber. The average molecular interchain spacing 〈R〉 in Angstroms of neat epoxy and epoxy–rubber blends were calculated from the strong maximum in the diffraction scan using established equations. The half-width 〈HW〉 of the maximum was used to qualitatively describe the distribution of 〈R〉. An increase in 〈R〉 value signifies formation of a separate packing order, as well as an increase in the free volume which, however, varies with the extent of compatibilization between epoxy cresol novolac and CTPB. Fourier transform infrared studies convincingly establish the crosslinking between the oxirane group of epoxy and the carboxyl group of CTPB as reflected in the characteristic peak shifts in the blends, compared with individual polymers. The merger of several peaks of individual polymers, as well as the appearance of minor peaks elsewhere, were also evident. Scanning electron microscopy studies have also been undertaken to study the phase morphology development, as well as changes in the fracture surface topography with varied CTPB content. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 537–543, 1998     

X-ray absorption near edge structure and X-ray photoelectron spectroscopy studies of chloride in passive oxide films

X-ray absorption near edge structure (XANES), utilizing both electron yield and X-ray fluorescence detectors, and X-ray photoelectron spectroscopy (XPS) were used to follow chloride uptake by oxide-covered aluminum in 0.1 M NaCl solutions. The aluminum samples were polarized at selected potentials below (less positive than) the pitting potential. The electron yield XANES and XPS showed multiple peaks. The XPS chloride spectra showed two distinct sets of doublets. One doublet is related to chloride on the surface and the second is related to chloride incorporated in the oxide film. The XANES results also showed two peaks which are attributed to chloride on the surface and in the bulk of the oxide.     

Atomic force microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and thermal studies of the new melamine fiber

This paper reports the characterization of unaged and aged melamine fibers using various characterization techniques including atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. Since melamine fiber is a relatively new fiber, very few studies on its characterization have been made. Morphological studies of the fiber surface using SEM display die lines running along the filament surface, which are characteristics of synthetic fibers and generally occur during spinning of the molten prepolymer through the spinnerets. AFM studies show that the surface of a melamine fiber filament contains a large number of hills and valleys, which are triangular in shape. AFM roughness analysis shows that melamine fiber surface is considerably rough which may aid in adhesion of the fiber with polymeric matrices. Ageing causes an increase in the surface roughness with simultaneous increase in the crystallinity of the fiber from 19.4% to 22.6%. In XPS studies, high concentrations of carbonyl and hydroxyl groups on the filament surface have been detected. Ageing causes a reduction in the hydroxyl group concentration and an increase in the carbonyl group concentration due to surface oxidation. The reduction in the surface hydroxyl groups due to ageing has also been detected in the Fourier-Transform infrared (FT-IR) spectra of the aged fibers. Thermogravimetric (TG) studies reveal a high thermal stability of the melamine fiber even in an oxidative environment such as air.     

Mechanism of anodic oxidation of molybdenum in nearly-neutral electrolytes studied by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy

Anodic oxidation of molybdenum in weakly acidic, nearly neutral and weakly alkaline electrolytes was studied by voltammetric and electrochemical impedance spectroscopic measurements in a wide potential and pH range. Current vs. potential curves were found to exhibit two pseudo-Tafel regions suggesting two parallel pathways of the dissolution process. Electrochemical impedance spectra indicated the presence of at least two reaction intermediates. X-ray photoelectron spectroscopic (XPS) results pointed to the formation of an oxide containing Mo(IV), Mo(V) and Mo(VI), the exact ratio between different valence states depending on potential and pH of the solution. A physico-chemical model of the processes is proposed and a set of kinetic equations for the steady-state current vs. potential curve and the impedance response are derived. The model is found to reproduce quantitatively the current vs. potential curves and impedance spectra at a range of potentials and pH and to agree qualitatively with the XPS results. Subject to further improvement, the model could serve as a starting point for the optimization of the electrochemical fabrication of functional molybdenum oxide coatings.     

A reconsideration of the relationship between the crystallite size La of carbons determined by X-ray diffraction and Raman spectroscopy

Non-graphitic carbon materials produced by pyrolyzing wood at temperatures from 400 to 2400 °C and various types of commercial carbon fibers were examined by X-ray diffraction and Raman spectroscopy. The specimens cover a wide range of crystallite sizes L_a, in particular also very small sizes below 2 nm. The X-ray data were evaluated using the Scherrer equation and by an advanced approach using full curve fitting. The ratio of the D/G band intensities was determined from the Raman data by different evaluation techniques. A critical assessment of the classical linear relationship between 1/L_a and the D/G ratio shows that the relationship breaks down for crystallite sizes below 2 nm in accordance with recent theoretical predictions. The results are compared with data from the literature, showing that there are additional discrepancies between the data from various carbon types at large L_a due to different methods of data evaluation.     

In situ tensile damage characterization of C/C composites through X-ray computed tomography and digital volume correlation

Carbon fiber reinforced carbon matrix (C/C) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to obtain information about changes in the failure processes, a technology known as in situ X-ray computed tomography is used. In this paper, tensile loads were applied to 3D fine-woven punctured and needle-punched C/C composites perpendicular to the punctured and needle-punched directions. In situ X-ray computed tomography was employed to observe damage development, and digital volume correlation was used to assess the laboratory X-ray computed tomographs to measure local strains. Assimilation of pores is observed in C/C composites, with cracks evolving from original micro-pores. While fine-woven punctured C/C composites present an elegant linear failure, needle-punched C/C composites present a traditional non-linear failure. This difference is due to the different structures of the preforms. Furthermore, the C/C composites are weak at the sites where they are punctured or needle-punched.     

Characterization of complex die-pressed Al2O3 green compact using liquid immersion,X-ray tomography,and numerical simulations

This study examined the compaction behavior of a green ceramic component with a complex shape formed by die pressing at 50 MPa using spray-dried alumina. Compared to a simple cylindrical sample, the sample with a complex shape revealed a higher degree of microstructural inhomogeneity and crack formation. Granule deformation and pore distribution at different sample locations were observed by optical microscopy after infiltrating liquid into the voids of a green compact. The refractive index of the immersion liquid should be different slightly from that of alumina for better observations. X-ray micro-computed tomography was also used to visualize the pore distribution and crack shape. Numerical simulations based on the Drucker-Prager/Cap model were performed to distinguish the stress and displacement distribution within the compact. The significant stress gradient at the crack initiation point could explain crack formation, whereas the application of a higher pressure resulted in a further increase in stress gradient.     

Surface carbonation of synthetic C-S-H samples: A comparison between fresh and aged C-S-H using X-ray photoelectron spectroscopy

This paper presents a continuation of studies into silicate anion structure using X-ray photoelectron spectroscopy (XPS). A series of C-S-H samples have been prepared mechanochemically, and then stored under ambient conditions for six months. Storage led to surface carbonation, the extent of which was dependent upon the calcium/silicon ratio of the fresh sample. Carbonation arose through decalcification of the C-S-H, leading to increased silicate polymerisation. The surfaces of the most calcium-rich phases (C/S = 1.33 and 1.50) underwent complete decalcification to yield silica (possibly containing some silanol groups) and calcium carbonate. Carbonation, and hence changes in silicate anion structure, was minimal for the C-S-H phases with C/S = 0.67 and 0.75.     

Synthesis and Raman characterization of boron-doped single-walled carbon nanotubes

A systematic study was carried out to dope single-walled carbon nanotube (SWNT) bundles with varying amounts of boron using the pulsed laser vaporization technique. Targets containing boron concentrations ranging from 0.5 to 10 at.% boron were prepared by mixing elemental boron with carbon paste and the Co/Ni catalysts. The laser-generated products that were obtained from these targets were characterized by high resolution transmission electron microscopy, electron energy loss spectroscopy (EELS), thermoelectric power (TEP) measurements, and Raman scattering experiments. Electron microscopy and Raman studies revealed that the presence of various levels of boron concentration in the target strongly affected the products that were prepared. SWNTs were found in the products prepared from targets containing up through 3 at.% boron, and high resolution EELS estimated that less than 0.05-0.1 at.% boron is present in the SWNT lattice. The absence of SWNT bundles in the products derived from targets containing more than 3 at.% boron implies that the presence of excess boron in the carbon plume severely inhibits the carbon nanotube growth. The overall effect of the boron incorporation primarily leads to: (i) a systematic increase in intensity of the disorder-induced band (D-band) upon boron doping, with increasing D-band intensity observed for higher doping levels, (ii) a systematic downshift in the G′-band frequency due the relatively weaker C-B bond, and (iii) a non-linear variation in the RBM and G′-band intensities which is attributed to shifts in resonance conditions in the doped tubes. Resonant Raman spectroscopy thus provides large changes in the intensity of prominent features even when the dopant concentration is below the detectable limit of EELS (0.05-0.1 at.%). Thermoelectric power data also provide complementary evidence for the presence of a small boron concentration in the SWNT lattice which transforms the SWNTs into a permanently p-type material.     

Studies of Cu-ZSM-5 by X-ray absorption spectroscopy and its application for the oxidation of benzene to phenol by air

The oxidation of benzene to phenol has been successfully carried out in air over Cu-ZSM-5 at moderate temperatures. Several parameters such as Cu loading, calcination temperature and co-exchanged metal ions influence the nature of the catalyst. At low Cu loadings, the catalyst is more selective to phenol while at high Cu loadings CO₂ is the major product. In situ H₂-TPR XAFS studies reveal that at low Cu loadings, Cu exists as isolated pentacoordinated ions, with 4 equatorial oxygens at 1.94 Å and a more distant axial oxygen at 2.34 Å. At higher loadings, monomeric as well as dimeric Cu species exist, with a Cu–Cu distance of 2.92 Å. This suggests that the isolated Cu sites are the active sites responsible for phenol formation. When the catalyst was calcined at 450 °C, the activity peaked in the first hour and then slowly deactivated, but when the calcination temperature was increased to 850 °C, the activity slowly increased until it reached a plateau. Analysis of the XANES region during in situ H₂-TPR shows that at lower calcination temperatures two reduction peaks are present, corresponding to Cu²⁺ → Cu⁺ and Cu⁺ → Cu⁰. At high calcination temperatures, only a small fraction of the Cu undergoes the two-step reduction and most of the Cu remains in the +2 state. Slow deactivation of the catalyst calcined at 450 °C is due to migration of the Cu ions to inaccessible sites in the zeolite; at high calcination temperatures the Cu is tightly bound to the framework and is unable to migrate. EXAFS analysis of the sample calcined at 850 °C reveals two Cu–Si(Al) scattering paths at 2.83 Å. Doping the catalyst with other metals, in particular Ag and Pd, further improves the activity and selectivity of the reaction. The addition of water to the reaction increases the selectivity of the reaction by displacing the product from the active site.     

Biaxial orientation in HDPE films: comparison of infrared spectroscopy, X-ray pole figures and birefringence techniques

In this study, high-density polyethylene films (HDPE) were produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous and global orientation factors using birefringence, Fourier transform infrared spectroscopy (FTIR) using a tilted incidence technique and X-ray pole figures. Evaluation of a simplified FTIR procedure without using the tilted method for the determination of crystalline orientation factors proposed in the literature is also evaluated and assessed. The results indicate that FTIR overestimate the crystalline orientation factors, particularly for the crystalline a-axis. Significant discrepancies are also observed for the b-axis orientation, which may be due to an overlap of the amorphous contribution and/or saturation of FTIR bands. Those differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from combination of X-ray and birefringence.     

X-ray photoemission spectroscopy study on the effects of functionalization in fulleropyrrolidine and pyrrolidine derivatives

Fulleropyrrolidine and pyrrolidine derivatives were studied using X-ray photoemission spectroscopy in order to determine the effects of the C₆₀-cage on the pyrrolidine nitrogen, as well as the influence of further derivatisation. Charge transfer from the carbon pyrrolidine ring to the C₆₀-cages is observed and this charge redistribution influences not only the carbon atoms but also the nitrogen. The major influence of different functionalization groups on the pyrrolidine nitrogen is whether or not they lead to quaternisation while no differences could be detected for different groups (methyl group or alkyl chain) producing one or the other configuration. However, the type of counter ion is important for the stability of the pyrrolidinium nitrogen: demethylated nitrogen, always found to be present in iodide counter balanced compounds, disappears in compounds counter balanced with anion.