ABSTRACT
Perfluorosulfonated ionomers are the most successful ion-exchange membranes at an industrial scale. One recent, cutting-edge application of perfluorosulfonated ionomers is in polymer electrolyte fuel cells (PEFCs). In PEFCs, the ionomers are used as a component of the catalyst layer (CL) in addition to functioning as a proton-exchange membrane. In this study, the microstructures in the CLs of PEFCs were characterized by combined synchrotron X-ray scattering and transmission electron microscopy (TEM) analyses. The CL comprised a catalyst, a support, and an ionomer. Fractal dimensional analysis of the combined ultrasmall- and small-angle X-ray scattering profiles indicated that the carbon-black-supported Pt catalyst (Pt/CB) surface was covered with the ionomer in the CL. Anomalous X-ray scattering revealed that the Pt catalyst nanoparticles on the carbon surfaces were aggregated in the CLs. These findings are consistent with the ionomer/catalyst microstructures and ionomer coverage on the Pt/CB surface obtained from TEM observations.
ABSTRACT
A technique for analyzing infrared imaging data based on two-trace two-dimensional (2T2D) correlation analysis is presented to extract pertinent information underlying spectroscopic imaging data. In 2T2D correlation mapping, each spectrum in hyperspectral data is individually compared with a reference spectrum to generate 2T2D asynchronous correlation intensity at the x- and y-coordinates on a 2T2D correlation map. Asynchronous correlation intensity develops only when the signal contribution from a certain species becomes even more significant in the sample spectrum compared with the reference spectrum. This feature can be advantageously utilized to examine molecular interaction or an intermediate form of the component present in a system of interest. 2T2D correlation mapping is examined using Fourier transform infrared imaging data of polymer composites based on polypropylene grafted with maleic anhydride melt-mixed with silica spheres. Infrared images derived by using conventional visualization based on a single wavenumber (i.e., 1713 cm-1) are dominated with the overwhelming infrared absorbance induced by the normal maleic anhydride species, making the identification of subtle but pertinent changes in the composite system difficult. A 2T2D correlation map derived from the maleic anhydride/silica spheres composite developed a significant asynchronous correlation intensity between the infrared bands at 1695 and 1713 cm-1 around a specific region on the map where the maleic anhydride and silica spheres coexist. On the other hand, such a correlation pattern becomes less acute when the silica spheres is modified with the octadecyldimethyl group to prevent the hydrogen bonding with the maleic anhydride. It thus revealed that the silanol groups on the surface of the silica spheres substantially interact with the maleic anhydride via the development of the hydrogen bonding.
ABSTRACT
A binary amorphous polymer blend consisting of polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) was studied with a rheo-optical characterization technique based on the combination of a near-infrared (NIR) spectrometer and a tensile testing machine. In rheo-optical NIR spectroscopy, tensile deformations were applied to polymers to induce the displacement of molecular chains while being probed by NIR light. The application of this technique was extended to a partially miscible amorphous polymer blend consisting of PVC and PMMA to demonstrate how it can be utilized to detect subtle but important deformation behavior. A change in the NIR spectral feature revealed that the initial deformation of the blend induces the reorientation of the PVC chains. A part of the PMMA connected to the PVC was tagged during the PVC deformation. Further deformation of the sample eventually resulted in necking propagation to the surrounding area.
ABSTRACT
We have developed a novel rheo-optical Fourier-transform infrared (FTIR) imaging technique that can probe the molecular-scale deformation behavior of a polymer matrix in composite materials. This rheo-optical FTIR imaging is based on in situ-polarized FTIR imaging of a polymer sample while it is being deformed by mechanical force. This imaging technique readily captures the orientation of the polymer molecules resulting from the applied strain. Analysis of the resulting FTIR imaging data by disrelation mapping makes it possible to further elucidate subtle but pertinent spectral variations arising from changes in the state of molecules within the spectroscopic images. In this study, the rheo-optical FTIR imaging is applied to analysis of the deformation behaviors of a composite composed of polypropylene containing hydroxyl groups (PPOH) and silica spheres (SS) to investigate matrix-filler adhesion of the composite. Our rheo-optical FTIR imaging analysis revealed selective inhibition of PPOH orientation at the matrix-filler interface during tensile deformation due to high matrix-filler adhesion via hydrogen bonding. The strong link between the PPOH matrix and SS filler efficiently restricts mobility of the matrix, resulting in the reinforcement of PPOH by addition of SS. Rheo-optical FTIR imaging is an effective tool for probing localized deformation behavior at the matrix-filler interface as well as achieving a better understanding of the correlation between matrix-filler adhesion and the effective reinforcement of composites.
ABSTRACT
Isocyanurates are cyclic trimers of isocyanate molecules. They are generally known as highly thermostable compounds. However, it is interesting how the thermal stabilities of the isocyanurate molecules will be altered depending on the substituents of their three nitrogen atoms. We performed computational investigations on the thermochemical behaviors of isocyanurate molecules with various alkyl and phenyl substituents. The cyclotrimerization processes of isocyanates are highly exothermic. Our best estimate of the enthalpy change for the cyclotrimerization of methyl isocyanate into trimethyl isocyanurate was -66.4 kcal mol-1. Additional negative cyclotrimerization enthalpy changes were observed for n-alkyl-substituted isocyanates. This trend was enhanced with an extension of n-alkyl chains. Conversely, low negative cyclotrimerization enthalpy changes were shown for secondary and tertiary alkyl-substituted isocyanates. The n-alkyl-substituted isocyanurates were shown to be stabilized due to attractive dispersion interactions between the substituents. Meanwhile, the branched alkyl-substituted isocyanurates were destabilized due to the deformation of their isocyanurate rings. For various alkyl-substituted isocyanates, the sum of the deformation energy of the isocyanurate ring and the intramolecular inter-substituent nonbonding interaction energies was found to be linearly correlated with their cyclotrimerization energies. The cyclotrimerization energy for phenyl isocyanate was shown to have significantly deviated from the linear relationship observed for the alkyl-substituted isocyanurates. This is probably attributable to a remarkable change in the orbital resonance interactions during the cyclotrimerization of phenyl isocyanate to triphenyl isocyanurate.
ABSTRACT
A rheo-optical characterization technique based on the combination of near-infrared (NIR) spectroscopy and mechanical analysis was applied to the nanocomposite consisting of hydroxyl-functionalized polypropylene (PPOH) and mesoporous silica (MPS) to probe the deformation behavior. Substantial levels of spectral changes of NIR spectral features were captured when the polymer samples underwent tensile deformation. Sets of spectra were subjected to projection treatment to remove the effect of baseline fluctuations and thickness change inevitably caused by the tensile deformation of the sample. Then, two-trace two-dimensional (2T2D) correlation spectroscopy was applied to the pretreated spectra to elucidate spectroscopic signature associated with the difference between the initial and deformed samples. An asynchronous correlation peak appears between the bands at 1720 and 1700 nm respectively reflecting the contributions of predominantly amorphous and crystalline component of the PPOH, indicating the predominant variation of amorphous structure followed by that of crystalline structure. In addition, the predominant spectral change related to the amorphous band becomes even more acute by including the MPS with large pores. It is hence likely that the larger pore size of the MPS confines the more amorphous structure, which, in turn, causes simultaneous reorientation of the polymer chains in the amorphous region during the elastic deformation. Consequently, the incorporation of the MPS selectively restricts the deformation of the amorphous structure which eventually provides the obvious increase in the mechanical property of the PPOH polymer.
ABSTRACT
Hydrogen/deuterium (H/D) exchange of gelatinized starch was probed by in-situ near-infrared (NIR) monitoring coupled with two-dimensional (2D) correlation spectroscopy. Gelatinized starch undergoes spontaneous H/D exchange in D2O. During the substitution, the exchange rate essentially becomes different depending on solvent accessibility of various parts of the molecule. Thus, by analyzing the change in the NIR feature observed during the substitution, it becomes possible to sort out local structure and dynamics of the system. 2D correlation analysis of the time-dependent NIR spectra reveals the presence of different local structure of the starch, each having different solvent accessibility. For example, during the H/D exchange, the D2O is first absorbed by starch molecules especially around the surface area between the starch and water, where the water molecules are weakly interacted with the starch molecules. This absorption is quickly followed by the development of HDO species. Further absorption of the D2O results in the penetration of the molecules inside the starch and eventually develops the relatively strong interaction between the HDO and starch molecules because of the presence of dominant starch molecules.
ABSTRACT
Tensile deformations of a partially miscible blend of polymethyl methacrylate (PMMA) and polyethylene glycol (PEG) is studied by a rheo-optical characterization near-infrared (NIR) technique to probe deformation behavior during tensile deformation. Sets of NIR spectra of the polymer samples were collected by using an acousto-optic tunable filter (AOTF) NIR spectrometer coupled with a tensile testing machine as an excitation device. While deformations of the samples were readily captured as strain-dependent NIR spectra, the entire feature of the spectra was overwhelmed with the baseline fluctuation induced by the decrease in the sample thickness and subsequent change in the light scattering. Several pretreatment techniques, including multiplicative scatter collection (MSC) and null-space projection, are subjected to the NIR spectra prior to the determination of the sequential order of the spectral intensity changes by two-dimensional (2D) correlation analysis. The comparison of the MSC and null-space projection provided an interesting insight into the system, especially deformation-induced variation of light scattering observed during the tensile testing of the polymer sample. In addition, the sequential order determined with the 2D correlation spectra revealed that orientation of a specific part of PMMA chain occurs before that of the others because of the interaction between CO group of PMMA and terminal OH group of PEG.
ABSTRACT
Near infrared (NIR) imaging data of poly(lactic) acid (PLA) nanocomposite were analysed by disrelation mapping to prove the possible interaction between PLA matrix and montmorillonite-based nanoclay. The basic concept of disrelation mapping can be viewed as a spatial filter based on two-dimensional (2D) correlation function to elucidate specific areas where disrelated variation between intensities occurs. Correlation intensity develops on disrelation map only if spectral intensities at v1 and v2 within the local spatial area vary in a dissimilar manner. This feature is especially suitable for identifying the area where interaction between components occurs, which is not fully detected by the conventional visualizations based on a single wavenumber. Disrelation maps constructed with NIR bands arising from the crystalline and amorphous components of the PLA. The pattern appearing on the disrelation map indicated different distributions of the crystalline and amorphous components of the nanocomposite sample. In addition, the development of disrelation intensity becomes acute especially at the area adjacent to the clay, revealing that the clay essentially works as nucleating agent to cause the additional development of crystalline structure of PLA by lowering the surface energy barrier.
ABSTRACT
A novel technique called disrelation spectroscopic imaging describes the process of identifying an area where a coordinated or out-of-phase change in pattern of spectral absorbance occurs. Disrelation mapping can be viewed as a spatial filter based on the well-established two-dimensional (2D) correlation function to highlight specific areas where disrelated variation occurs between ν1 and ν2. Disrelation intensity develops only if the spectral absorbance measured at ν1 and ν2 vary out of phase with each other within a specific spatial area. The disrelation mapping locates regions where absorbance varies in a dissimilar manner because of the contribution from species of different physical or chemical origins. Consequently, it becomes possible to probe onset of molecular interactions or presence of intermediate forms between components, which is not fully detected by the conventional visualizations based on a single wavenumber. Data analysis using disrelation mapping applied to Fourier transform infrared (FT-IR) spectroscopic images is presented in this study. Data sets of FT-IR spectroscopic images of blends of poly(methyl methacrylate) (PMMA) and polyethylene glycol (PEG) were subjected to the disrelation mapping. It was found that the disrelation intensity between 1730 and 1714 cm-1 becomes especially acute around the spatial boundary between PMMA and PEG domains within the studied blend sample. Thus the band at 1730 cm-1 most likely represents the C=O stretching mode of the C=O···H-O species due to the intermolecular hydrogen bonding between PMMA and PEG. The appearance of such disrelation is more noticeable in the PEG-rich region, for the PEG with low molecular weight. Consequently, it suggests that the blends of PMMA and PEG are partially miscible at the molecular level and these intermolecular interactions are affected by the quantity of the terminal -OH groups of the PEG.
ABSTRACT
High-resolution matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS) was used for the analysis of the low-molecular-weight products from the photo-oxidation of poly(3-hexylthiophene) (P3HT) in solution and thin film. Eight new peak series were observed in the low-mass range of the mass spectra of the products degraded in solution, and the formulas of the eight components were determined from the accurate mass. From SEC/MALDI-TOF MS, two components were identified as the degraded products, and the other six components were derived from the fragmentation of the degraded products during the MALDI process. A mechanism for the formation of these components was proposed on the basis of the results of MALDI-TOF MS. For the thin film degradation, a part of products in the solution degradation were observed, which supports that the oxidation of P3HT in solution and thin film proceeded in the same mechanism. This study shows that high-resolution MALDI-TOF MS is effective for the analysis of the low-molecular-weight products from P3HT photo-oxidation and expected to be feasible for the degradation analyses of other polymers. Copyright © 2015 John Wiley & Sons, Ltd.
ABSTRACT
Flammability limits were measured for a number of olefinic and saturated fluoro-compounds in a 12l spherical glass vessel. The obtained data together with the ones of previous studies have been analyzed based on the F-number scheme of flammability limits. The flammability limits of these compounds have been found to be explained very well by the present scheme of interpretation. The flammability limits are dependent upon distribution of F atoms in a molecule as well as upon F-substitution rate itself. It has been found that -O-CF(3) group in a molecule conspicuously decreases the flammability of the compound, while -C-CF(3) group does not much. For olefinic compounds, distribution of F atoms around double bonds markedly diminishes the flammability of the molecule.
