Reikichi Iwamoto

Experimental Proof of the Relation Between Thickness of the Probed Surface Layer and Absorbance in FT-IR/ATR Spectroscopy

Experimental investigation has been made of the relation of absorbance of a band in FT-IR/ATR spectroscopy to the thickness of the probed surface layer from the measurements of two-layered samples. The two-layered samples are composed of a polystyrene surface layer varying in thickness from 0.01 to 3.64 μm and a polyurethane base layer of 100 *im thickness. The component spectrum of the surface or base layer was separated by spectral subtraction. FT-IR/ATR spectroscopic measurements were mostly measured by nonpolarized incident light. The relation of observed absorbances of several selected bands of both the surface and base layers to the thickness of the surface layer was compared with the theoretical calculations from Harricks equation. In the comparison, the effect of “nonpolarization” of the incident light was corrected for the observed absorbances. The agreement was excellent between the observation of and the theoretical calculation for both the surface and base layers. A method was proposed to determine the thickness of the spectrally separable surface layer on a film. The usefulness of this method was demonstrated by application to the redetermination of the thickness of the surface layer of the present two-layered samples. An expression was proposed to give the contribution of a surface layer of a certain thickness to the total absorbance of a band in ATR spectroscopy.

Total internal reflection Raman spectroscopy

Feasibility of total internal reflection (TIR) Raman spectroscopy as a new tool for characterizing thin surface layers has been investigated, starting with selection of the material for the internal reflection element (IRE). Sapphire was found to be the most suitable for the IRE among TiO2, SrTiO3, several kinds of flint glasses, and sapphire itself. The potential of TIR Raman method was proved by measurements on the two‐layered samples consisting of a thin surface layer of polystryene and a base layer of polyethylene. The thickness of the surface layer that could be measured by the present technique was then extensively investigated for the two‐layered samples which had the surface layer of polystryrene varying in thickness (0.006–0.93 μm) and the base layer of a constant thickness of polycarbonate (12 μm). We could measure vibrational spectra of the surface layers as thin as 0.006–0.2 μm sufficiently separately from those of the base layer. Thickness of the measurable surface layer could be varied to a ...

Quantitative Surface Analysis by Fourier Transform Attenuated Total Reflection Infrared Spectroscopy

The Fourier transform infrared spectroscopic ATR (FT-IR-ATR) method has been applied to quantitative determination of chemical composition of thin surface layers. The powerful capability of the FT-IR-ATR spectral subtraction method was proved to determine poly(dimethylsiloxane) content in the surface layer of Cardiothane 51, which consists of poly(urethane) and poly(dimethylsiloxane) as a minor component, showing the detection limit of 0.2% of the content. An absorbance ratio of a selected band of poly(dimethylsiloxane) relative to a selected band of poly(urethane) was determined by FT-IR-ATR measurements on the pure samples of each of the constituting components that have the same area contacted onto the internal reflection element of Ge. Consideration was also given to the thickness of the surface layer that can be analyzed by the present method, and one half of the penetration depth dp was considered to better represent the thickness of the surface layer measured than dp.

Total Internal Reflection Raman Spectroscopy at the Critical Angle for Raman Measurements of Thin Films

Total internal reflection Raman spectroscopy at the critical angle has been shown to be useful for Raman measurements of not only thin films but also of any samples that can be directly coated or intimately contacted on the internal reflection element (IRE). Usefulness of this technique was demonstrated for a polystyrene film (0.70 μm thick) coated on the IRE, signal enhancement being 40 as compared with the conventional normal illumination. The technique was also applied to a thin coating layer of bovine albumin on the IRE to give the spectrum of excellent signal/noise ratio.

Infrared study on molecular conformations of dialkoxyethanes and related compounds

Abstract Infrared spectra have been taken of the following groups of liquids: Group I, CH 3 OCH 2 CH 2 OCH 3 , CH 3 CH 2 OCH 2 CH 2 OCH 2 CH 3 , CH 3 OCH 2 CH 2 OCH 2 CH 2 OCH 3 ; Group II, CH 3 OCH 2 CH 2 OH, CH 3 CH 2 OCH 2 CH 2 OH, HOCH 2 CH 2 OCH 2 CH 2 OH; Group III, CH 3 OCH 2 CH 2 OCH 2 CH 2 OH, CH 3 CH 2 OCH 2 CH 2 OCH 2 CH 2 OH. The spectra of the compounds were compared with those of the liquids containing mercuric chloride and the resulting crystalline complexes of the compounds with mercuric chloride. Distinctive differences are observed in the spectral feature especially in the 1150–1050 cm −1 region between pure liquids, liquids with mercuric chloride and crystalline complexes in the case of group I liquids, while the corresponding differences in spectra are not observed among the three states in the infrared spectra for group II. The corresponding differences, although not so conspicuous as in the case of group I, are observed for the spectral features for group III. The experimental facts have led us to the following conclusion. A trans form is more stable than a gauche form around a CH 2 -CH 2 bond in the liquid state in the case of group I, while a gauche form is more stable than a trans form around the bond in the case of group II because of hydrogen bonding between an oxygen atom of ether linkage and a hydroxyl group. For the compounds of group III, a CH 2 -CH 2 bond neighboring an alkoxy group is mainly of a trans form, whereas the bond joined to an OH group is dominantly of a gauche form.

Infrared and Near-Infrared Study of the Interaction of Amide C=O with Water in Ideally Inert Medium

Hydration property of amide C=O was investigated from the OH stretching fundamentals and the first combinations of the water in the hydrate, formed in hydrophobic solution of an N,N-dialkyl amide ((CH(3)CH(2))(2)NCO(CH(2))(10)CH(3)) in heptane. The property was also examined for ester C=O of an alkyl ester (CH(3)(CH(2))(8)COOCH(3)) for comparison. The hydrates of C=O...H-O-H (I) and C=O...H-O-H...O=C (II) occur, the latter emerging above 5% concentration only and increasing in relative population with increasing concentration. The free OH of the water in I shows a sharp stretching band (nu(1)(OH(f))) at about 3690 cm(-1) and the bonded OH shows a much broader stretching band (nu(1)(OH(b))) of a significantly lower frequency. The difference Deltanu(fb) (= nu(1)(OH(f))-nu(1)(OH(b))), which is used as an indicator of hydration ability, is much larger for amide C=O (205 cm(-1)) than for ester C=O (134 cm(-1)). Equilibrium constant k(H) for the hydration process [C=O + (H(2)O) <--> C=O...H-O-H] is larger by about ten times for amide C=O than for ester C=O. Factors Deltanu(fb) and k(H) demonstrate that amide C=O has a strong hydration ability, implying that amide C=O of peptide linkage has an important contribution to high hydration ability of proteins.

Characterization of infrared and near-infrared absorptions of free alcoholic OH groups in hydrocarbon.

We have demonstrated that the near-infrared and infrared absorptions in the 8000–3200 cm−1 region of an OH group of 2-nonanol, 1-nonanol, etc., in n-heptane are excellently separated by subtraction without any serious interference down to very low concentrations at which OH groups are completely free. The separated sharp absorptions are assigned to the fundamental, combination, and overtone bands that are concerned with the OH stretching of free OH. Two components of a sharp overtone band around 7100 cm−1, which are observed for primary and secondary alcohols, are assigned to coexisting internal rotational isomers of an OH group around the O–C bond. The frequencies of the OH stretching fundamental and overtone bands that are assigned to internal rotational positions are consistent for all the investigated alcohols, including methanol and tertiary butanol. Comparison of the separated spectrum of 2-nonanol in n-heptane with that in 1-chlorooctane or in carbon tetrachloride makes it clear that hydrocarbon is an inert solvent that does not disturb the intrinsic nature of an alcohol OH group. There actually exists a constant anharmonicity shift of 169–175 cm−1 between the double frequency (2v(OH)o) of the observed fundamental and the observed overtone frequency ([2v(OH)]o) for free OH of various alcohols in n-heptane.

FT-NIR Spectroscopic Study of OH Groups in Ethylene-Vinyl Alcohol Copolymer

In the present study we have demonstrated the unique capability of near-infrared/infrared (NIR/IR) spectroscopy to characterize the hydrogen bonding of the OH groups in ethylene-vinyl alcohol copolymer (EVOH). Fourier transform (FT)-NIR/IR spectroscopic measurements were made of EVOHs with ethylene contents of 33, 49, 75, and 89 mole %. A strong and broad absorption at ∼ 4780 cm−1, which is the first combination of the OH stretching and deformation vibrations, is assigned to the aggregated OH groups. The band shows a shoulder at 4970 cm−1 at an ethylene content of 49 mole %, which becomes a distinct peak at a content of 89%. This feature is assigned to the free OH group isolated in the surroundings of the ethylene component. Existence of the free OH group is additionally evidenced by the appearance of sharp absorptions of the OH stretching fundamental at 3027 cm−1 and its first overtone at 7094 cm−1. The relative population of the free OH has been estimated as 0, 0.3, 1.5, and 3.9 mole % for ethylene content of 33, 49, 75, and 89, mole %, respectively.

Infrared spectroscopic study of the effect of electrostatic interaction on the molecular arrangement in the hydration shell around Li+ in a nafion membrane.

In the present paper we characterize the hydration shell around a Li ion, as -SO(3)(-)Li(+), from a series of infrared spectra of the hydrated Li salt in a sample of Nafion. The infrared spectrum significantly changes through prolonged dehydration under a controlled flow of drying gas, to a limiting dryness level. We found that the Nafion membrane contains a small population of the SO(3)(-)Li(+) group isolated in a hydrophobic matrix (denoted A) in addition to the main component of the clustered group (B). The second hydration shell around A evaporates at moderate levels of dehydration, followed by partial evaporation of the first hydration shell during the final stage. In contrast, in the hydration shell around B, which occupies a hydrophilic environment, the innermost layer of the second shell still remains unevaporated under full dehydration conditions. From the hydration shell around A, we were able to resolve the distinct fundamental bands nu(3), nu(1), and nu(2) of the water that is coordinated to Li(+) in the first hydration shell. From analysis of the infrared spectrum of the hydration shell around B, we found that the strong electrostatic field of Li(+) brings about a molecular arrangement that is less favorable for intermolecular hydrogen-bonding in the inner second hydration shell. This structural effect occurs to a minor extent for the second hydration shell around a Na ion, which has a significantly weaker electrostatic field.

Near-infrared combination and overtone bands of the CH2 sequence in CH2X2, CH2XCHX2, and CH3(CH2)5CH3 and their characteristic frequency zones.

We characterized near-infrared spectra of the CH2 sequence in CH2X2 (X = halogen), CH2ClCHCl2, and CH3(CH2)5CH3. Each near-infrared absorption in the region from 3500 to 10 000 cm−1 is consistently assigned to one of the five different combination or overtone groups, in the order of increasing frequency, of the {[v(CH)]+[δ(CH)]} (A), {[v(CH)]+[2δ(CH)]} (B), [2v(CH)] (C), {[2v(CH)]+[δ(CH)]} (D), and [3v(CH)] (E) types, where v(CH) and δ(CH) denote the CH stretching and CH deformation normal modes, respectively. Each group has its own characteristic frequency zone. The bands of B, D, and E, which are second-order combinations or overtones, are weaker by 1/10–1/50 than those of A and C, which are first-order combinations or overtones. The near-infrared spectra of the CH2 sequence show “window zones” of very weak or no absorptions. This suggests that we can perceive the characteristic near-infrared bands of a functional group through the window zones, and we give an example to demonstrate this. The first-order combination bands of type A only of CH2X2 are reasonably assigned to a pair of the normal modes of v(CH) and δ(CH). From this we predict that the first-order combination bands should give structural information on the CH2 chain, similar to the infrared fundamental bands.