Reflectance-absorbance infrared spectroscopy

Modern methods of vibrational analysis have shown themselves to be unexpectedly powerful tools to study two-dimensional monomolecular films at gas/liquid interfaces. In particular, current work with external reflection-absorbance infrared spectroscopy has been able to derive detailed conformational and orientational information concerning the nature of the monolayer film. The LE-LC first order phase transition as seen by IR involves a conformational gauche-trans isomerization of the hydrocarbon chains a second transition in the acyl chains is seen at low molecular areas that may be related to a solid-solid type hydrocarbon phase change. Orientations and tilt angles of the hydrocarbon chains are able to be calculated from the polarized external reflectance spectra. These calculations find that the lipid acyl chains are relatively unoriented (or possibly randomly oriented) at low-to-intermediate surface pressures, while the orientation at high surface pressures is similar to that of the solid (gel phase) bulk lipid. 

Studies of carbonate-sulfonate RMs in engine oil on the antiwear performance of ZDDP, using reflectance-absorbance infrared spectroscopy RAIR, X-ray photoelectron spectroscopy XPS and Auger electron spectroscopy AES, showed that the tribofilms were inorganic amorphous phosphates, mainly orthophosphate (P043 ) and pyrophosphate (P2074 ) associated with zinc and magnesium (from the hard-core RMs) (Willermet et al., 1991 and 1992). 

XRF = X-ray fluorescence spectroscopy, XPS = X-ray photoelectron spectroscopy, AES = Auger electron spectroscopy, XANES = X-ray absorption near edge spectroscopy, RAIR = Reflectance-absorbance infrared spectroscopy, EXAFS = X-ray absorption fine-structure spectroscopy, ECR = Electric contact resistance, NMR = Nuclear magnetic resonance spectroscopy, IPS = Imaging photoelectron spectromicroscopy. 

Additional detailed characterization studies of PP/HA using cyclic voltammetry, scanning electron microscopy, x-ray photoelectron spectroscopy, and reflectance-absorbance infrared spectroscopy are described elsewhere 10). 

Fundamental studies by reflection angle infrared spectroscopy of the bonding of EME coupling agents to metal oxides reveal a significant shift in the carbonyl absorbance band when the coupling agent is applied as a very thin layer on a metal oxide. The shift is reproducible and the extent varies with the type of oxide. These results were obtained both by use of copper mirrors and from CuzO powder coated with very thin layers of model compounds. The compounds were not removable by isopropanol, a solvent for the bulk compound. The thiol absorbances of thin layers of model compounds were also found to decrease in relative intensity with time. This illustrates that a specific chemical interaction has occurred. 

Many investigations of the molecular structure of thin films formed by y-APS deposited onto inorganic substrates from aqueous solutions have been carried out. Ondrus and Boerio [2] used reflection-absorption infrared spectroscopy (RAIR) to determine the structure of y-APS films deposited on iron, 1100 aluminum, 2024 aluminum, and copper substrates from aqueous solutions at pH 10.4. They found that the as-formed films absorbed carbon dioxide and water vapor to form amine bicarbonate salts which were characterized by absorption bands near 1330, 1470, 1570, and 1640 cm-1. y-APS films had to be heated to temperatures above about 90°C in order to dissociate the bicarbonates, presumably to free amine, carbon dioxide, and water. Since the amine bicarbonates failed to react with epoxies, the strength of adhesive joints prepared... 

Some of the techniques described in this chapter used most widely today are Auger electron spectroscopy, X-ray photoelectron spectroscopy, electron-probe micro-analysis, low energy electron diffraction, scanning electron microscope, ion scattering spectroscopy, and secondary ion mass spectroscopy. The solid surface, after liberation of electrons, can be analyzed directly by AES, XPS, ISS, and EPMA (nondestructive techniques), or by liberation of ions from surfaces using SIMS (involving the destruction of the surface). Apart from the surface techniques, reflectance-absorbance infrared (RAIR) spectroscopy has also been employed for film characterization (Lindsay et al., 1993 Yin et al., 1993). Some... 

An example of direct examination is Ae examination of the polymer film by infrared or ultra-violet spectroscopy or of Aicker sections of polymer by attenuated total reflectance (ATR) infrared spectroscopy. Such techniques have severe limitations in that, because the additive is in effect heavily diluted with polymer, detection limits are usually well above the low concentration of additive present and Ais method is only applicable if the additive has distinct sharp absorption bands in regions where the polymer itself shows little or no absorption. In-situ spectroscopic techniques are not likely to be of value, then, in the analysis of samples of unknown composition. If known amounts of additive can be incorporated into additive-free polymer, however, these techniques are likely to be extremely useful in Ae study of solvent extraction procedures, and the study of additive ageing processes (ie. the effects of heat, light, sterilization, radiation, etc.), since the rate of disappearance of or decay can be measured directly by the decrease in absorbance of Ae sample at a suitable wave-lengA. 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

Infrared spectroscopy can provide a great deal of information on molecular identity and orientation at the electrode surface [51-53]. Molecular vibrational modes can also be sensitive to the presence of ionic species and variations in electrode potential [51,52]. In situ reflectance measurements in the infrared spectrum engender the same considerations of polarization and incident angles as in UV/visible reflectance. However, since water and other solvents employed in electrochemistry are strong IR absorbers, there is the additional problem of reduced throughput. This problem is alleviated with thin-layer spectroelectro-chemical cells [53]. 

Infrared spectroscopy has been a common tool for the study of solid surfaces (3). As in any surface spectroscopy, the number of adsorbed molecules and the surface area of the solid determines the sensitivity needed for IR studies. For low area surfaces, reflection techniques have been used to measure IR spectra of adsorbed monolayers on metal surfaces (7). However, for nonmetallic surfaces such as mica, the low reflectivity of mica makes reflection techniques less suitable for IR measurements. At the same time, the biaxial properties of mica, the parallel nature of the surfaces, and the absorbance of the mica itself present difficulties in IR spectroscopy (8). 

Other spectrophotometric techniques have been reported for the analysis of spironolactone. Near infrared diffuse reflectance first-derivative spectroscopy was used for determination of spironolactone in pharmaceutical dosage forms [30]. Readings were taken at 15 nm intervals, and then 81 absorbance readings were imput into a computer for principal component analysis. 

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