Fourier transform infrared compositional changes

For instance, in situ Fourier transform infrared (FTIR) spectroscopy has been used by Faguy etal. [176] to study the potential-dependent changes in anion structure and composition at the surface of Pt(lll) electrodes in H 804 -containing solutions. From the infrared differential normalized relative reflectance data, the maximum rate of intensity changes for three infrared bands can be obtained. Two modes associated with the adsorbed anion... 

Subramanian, A. (2009). Monitoring flavor quality, composition and ripening changes of Cheddar cheese using Fourier-transform infrared spectroscopy. PhD Thesis, The Ohio State University, p. 121. 

The most attractive sensors now being developed are the Fourier transform infrared spectrometer (FTIR) and the near-infrared (NIR) spectrometer for the on-line measurement of composition changes in complex media during cultivation. The FTIR measurements are based on the type and quantities of infrared radiation that a molecule absorbs. The NIR measurements are based on the absorption spectra following the multi-regression analyses. These sensors are not yet available for fermentation processes. 

Specular reflection Fourier transform infrared spectroscopy, performed with the beam striking the sample at 45- from the surface normal, was also used for in situ studies of the catalytic reaction. This technique makes it possible to observe changes in the gasphase composition [4-5]. The broad band reflectivity of the overlayer can be used to obtain the composition of a thin oxide film [6], Infrared spectra have been obtained from polycrystalline samples and from Cu(llO). The former samples are akin to the ones used for mass spectrometric studies. Distinguished from those studies our FTIR work was performed with a reaction vessel at room temperature. The sample was in this case resistively heated by tantalum wires. This combination separates the gas temperature from the temperature of the catalyst. The temperature of the impinging molecules is a... 

Pulse thermal analysis (PulseTA ) [1] eliminates, or at least reduces, the difficulties mentioned above. PulseTA is based on the injection of a specific amount of the gases or liquids into the inert carrier gas stream and subsequent monitoring of changes in the mass, enthalpy and gas composition, resulting from the incremental reaction extent. Because a known amount of the selected gas, which can be used for calibration, is injected into the system, the method is also suitable for quantification of the evolved gas by mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTTR). In contrast to conventional TA and all its modifications, the reaction is controlled not only by the temperature, but also by a distinct change in the composition of the reactive atmosphere. 

Raman microspectroscopy is the fastest and most powerful tool for analysis of phase transformations in contact loading. It can additionally provide information on residual stresses and/or chemical changes in the surface layers. However, limited databases of Raman spectra and difficulties with the interpretation of Raman spectra, as well as low accuracy of existing predictive tools for calculations of Raman spectra of solids, make it necessary to complement Raman data with electron or X-ray diffraction studies. Fourier-transform infrared microspectroscopy is another technique that can provide useful information on structural and compositional changes in the surface layer. 

Fourier transform infrared step-scan photoacoustic spectroscopy was developed to study the composition of thermoplastic olefin films, as a function of depth below the surface. Infrared bands associated with talc, polypropylene (PP), and ethylene-propylene mbber (EPR) were used as depth-profiling probes to identify photoacoustic signals. Experiments were done at various modulation frequencies, enabling a stratification model to be developed. The uppermost layer (0-3 micrometre) showed large changes in talc and PP concentration, whilst the layer below showed a significant decrease in both the phases. In the third layer (6-9 micrometre), all three phases showed the maximum values. In the fourth layer (9-12 micrometre), the talc concentration reduced, whilst concentrations of EPR and PP were observed, decreasing with depth. 32 refs. 

Studies of this restructuring process have been carried out on PDMS with surfaces made hydrophilic by UV/ozone treatment, oxygen plasma, or corona discharge. In these cases, changes in surface composition were determined using chemical force microscopy,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, or atomic force microscopy. ... 

The characterization of surface structure for miscible blends is a more formidable task, requiring techniques that are sensitive to the composition of the blend within several nanometers of the surface. X-ray photoelectron spectroscopy (xps) provided the first direct and quantitative evaluation of surface composition and surface composition gradients for miscible polymer blends of poly(vinyl methyl ether) (PVME) and polystyrene (PS) (22,23). Since that time, the situation has changed dramatically with the advance of theory and the application of exciting new experimental techniques to this problem. In addition to xps and pendant drop tensiometry (22,23), forward recoil spectroscopy (28), neutron (29) and x-ray reflectivity (30), secondary ion mass spectroscopy (either dynamic or time-of-flight-static) (31,32), and attenuated total reflectance Fourier transform infrared spectroscopy (33-35), have been applied successfully to study surface segregation. The advent of these new tools has enabled a multitechnique experimental approach toward careful examination of the validity of current surface segregation theories (36-39). 

Heischer et al. [172] measured the interfacial tension reductirai credited to the complexation between carboxy-terminated PBD and amine-terminated PDMS, which were added to an immiscible blend of PBD and PDMS. The changes in interfacial tensimi resembled the behavior observed for block copolymer addition to homopolymer blends there is initially a linear decrease in interfacial tension with the concentration of functional homopolymer up to a critical concentration, at which the interfacial tension becomes invariant to further increases in the concentration of functional material. However, the formation of interpolymer complexes depends on the equilibrium between associated and dissociated functional groups and, thus, the ultimate plateau value for interfacial tension reduction is dependent on the functional group stoichiometry. A reaction model for end-complexation was developed in order to reproduce the interfacial tension reduction data with Fourier transform infrared spectroscopy applied to determine the appropriate rate constants. The model provided a reasonable qualitative description of the interfacial tension results, but was not able to quantitatively predict the critical compositions observed experimentally. 

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