Fourier transform infrared study of the effects of irradiation on polyethylene

Fourier transform infrared spectra have been obtained for polyethylene irradiated in oxygen and nitrogen atmospheres. The spectra before and after irradiation have been compared by digital subtraction. The difference spectra are indicative of changes caused by irradiation. Crosslinking and chain scission reactions produce the observed changes.     

Fourier transform infrared study of low-temperature CO adsorption on CuMgAl-hydrotalcite

Single-phase CuMgAl ternary hydrotalcite with (Cu+Mg)/Al atomic ratio of 3.0 and Cu/Mg atomic ratio of 1.0 was synthesized by coprecipitation. Thermoanalytical studies of this sample showed transformations in three stages in the temperature range up to ca. 900 K yielding mainly CuO phase. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic measurements showed the presence of carbonates even after calcination of the sample at 973 K. The genesis of Cu+ sites during thermal treatment in vacuo at different temperatures for this sample was followed by IR spectroscopy of CO adsorbed at low temperature. Essentially no Cu+ sites are present on a sample calcined at 723 K, consistent with X-ray photoelectron spectroscopic (XPS) data. However, sample subjected to activation (1 h of O2 treatment at 723 K followed by 1 h of evacuation at the same temperature) upon CO adsorption at 85 K unambiguously showed the presence of Cu+ sites. 12CO-13CO coadsorption studies confirmed the presence of dicarbonyls, which are converted to linear Cu+-CO species during evacuation at 85 K. Concentration of the accessible Cu+ sites increased with the increase in activation temperature up to 873 K and decreased with a further temperature rise. The copper sites on the sample are heterogeneously distributed and their distribution depends on the activation temperature. Two routes of reduction of Cu2+ to Cu+ are proposed: (i) autoreduction during evacuation and (ii) reduction by CO.     

Fourier transform infrared spectroscopy study of nanostructured nickel oxide

Nanostructured nickel oxide having different average particle sizes ranging from 3 to 16 nm were synthesized and Fourier transform infrared (FTIR) spectra of the samples were recorded in the far infrared (IR) region. The spectra were found to be dominated by surface mode absorptions with no distinct absorption corresponding to the bulk transverse optical mode. IR absorption coefficient, alpha, for the nanostructured NiO samples were calculated as a function of frequency using a macroscopic approach devised by Fuchs. The effects of crystalline geometry, numerical values of optical constants, filling factor and increased damping on the spectral features of the samples were analyzed. Though the simulations approximately reproduced the occurrence of a shoulder in the experimental spectra, the most intense peak in the simulated spectra was found to be about 50 cm(-1) above the corresponding experimentally observed peak. It was shown that the experimentally observed absorption maximum of all the samples were in close agreement with that determined using a microscopic theory based on the rigid ion model. The weak absorption peaks in the frequency region 60-100 cm(-1) appearing in the spectra of all the samples were identified as surface induced transverse acoustical modes, omegaTA, which became IR active due to the breakdown of translational symmetry in the nanocrystallites.     

Fourier transform infrared study of segmental orientation in polymer blends

The effect of the macromolecular plasticizer poly(-methyl--n-propyl--propiolactone), PMPPL, on the orientation of poly(vinyl chloride), PVC, has been studied by FTIR spectroscopy. The addition of PMPPL to PVC does not change significantly the degree of orientation of PVC segments. In blends, PMPPL chains are more oriented when the matrix is richer in PVC but the PMPPL orientation function always remains smaller than that of PVC segments.     

Fourier transform infrared study of uniaxially oriented atactic polystyrene

Infrared measurements of the dichroic ratio of atactic polystyrene absorption bands provide a valuable method of determination of the overall orientation of chains as well as the particular orientation of the trans conformational segments. The orientation process produces the alignment of the chains as well as an increase in the amount of trans conformational segments. A linear relationship is observed between birefringence and dichroic ratio for the absorption bands characteristic of overall orientation. A value of 35° ± 3° is obtained for the angle between the normal to the plane of the benzene ring and the chain axis from both infrared and birefringence determinations.     

Fourier transform infrared study of the gel form of isotactic polystyrene

Infrared spectra of isotactic polystyrene gel films are observed to be significantly different from those of amorphous and crystalline polymer, indicating that the gel form is in a different conformation than the usual 3₁ helical crystal structure. Computer-assisted subtraction indicates that approximately 35% of the chains participate in the gel component, effectively ruling out structural defects as the origin of the ordered gel component.     

Fourier transform infrared study of two truxene-based discotic liquid crystals

We have used FTIR absorption to study the crystalline and liquid-crystalline phases of 2,3,7,8,12,13-hexa-n-tetradecanoyloxy-truxene (HATX) and 2,3,7,8,12,13-hexa(4-n-undecyloxybenzoyloxy)truxene (HBTX). Both materials show pronounced changes in the CH₂ stretching mode frequencies at their melting points. In addition, HATX shows a transition at about 20°C below the nominal melting point in which the alkyl tails gain significant disorder. Benzene stretching modes and the CH₂ deformation modes show subtle changes at the D_rd → N transition of HBTX and at the D_rd → D_hd transition of HATX.     

Fourier transform infrared spectroscopy and theoretical study of dimethylamine dimer in the gas phase

Dimethylamine (DMA) has been studied by gas-phase Fourier transform infrared (FTIR) spectroscopy. We have identified a spectral transition that is assigned to the DMA dimer. The IR spectra of the dimer in the gas phase are obtained by spectral subtraction of spectra recorded at different pressures. The enthalpy of hydrogen bond formation was obtained for the DMA dimer by temperature-dependence measurements. We complement the experimental results with ab initio and anharmonic local mode model calculations of monomer and dimer. Compared to the monomer, our calculations show that in the dimer the N-H bond is elongated, and the NH-stretching fundamental shifts to a lower wavenumber. More importantly, the weak NH-stretching fundamental transition has a pronounced intensity increase upon complexation. However, the first NH-stretching overtone transition is not favored by the same intensity enhancement, and we do not observe the first NH-stretching overtone of the dimer. On the basis of the measured and calculated intensity of the NH-stretching transition of the dimer, the equilibrium constant for dimerization at room temperature was determined.     

Matrix isolation Fourier transform infrared study of photodecomposition of formimidic acid

The UV isomerization of formamide (HCONH2) trapped in xenon, nitrogen, argon, and neon cryogenic matrices has been monitored by Fourier transform infrared (FT-IR) spectroscopy. Formamide monomer is the only species present in the matrices after deposition; when UV-selective irradiation was carried out at 240 nm, the n --> pi transition allowed us to observe the formation of several isomers of formimidic acid [H(OH)C=NH]. On these latter species, we carried out selective IR irradiation of their OH stretching mode and compared the experimental and theoretical (B3LYP/6-311+G(2d,2p)) sets of bands. This study allowed us to characterize for the first time all the isomers of formimidic acid. We have then studied the vacuum UV photodecomposition (lambda > 160 nm) of this molecule at 10 K in argon and xenon matrices. Several primary photoproducts such as HCN.H2O, HNC.H2O, and HNCO.H2 complexes, yielded by dehydration and dehydrogenation processes, were characterized.     

Fourier transform infrared studies on the thermal degradation of polyacrylonitrile

Fourier transform infrared studies of the thermal degradation of polyacrylonitrile (PAN) conducted at 200°C in air and under reduced pressure are presented. The spectra are markedly superior to those published previously. A mechanism consistent with the infrared results obtained under reduced pressure is advanced, and assignments for the infrared bands occuring in the spectrum of both the reduced pressure and air degraded PAN are given.     

Fourier transform infrared investigations of phosphate-silicate coatings on iron

The influence of silica addition and of the annealing on the structure and properties of phosphate coatings are investigated. It has been observed that silica stabilizes phosphates and reduces the transport of iron towards the surface.     

Fourier transform Raman spectroscopy in the visible region

Low-resolution (ca. 4cm^–1) Raman spectra of various liquids and solids, excited by an argon laser at 448 and 514.5 nm, were recorded using a BOMEM DA3.02 commercial interferometer. These spectra were compared with those obtained in the same experimental conditions on a conventional dispersive spectrometer. It is concluded that for low-resolution Raman studies with excitation in the visible region, the dispersive method is superior to the interferometric technique.     

Fourier transform infrared spectroscopic study of the photocatalytic degradation of cancerous cells on titanium dioxide

The method of attenuated total internal reflection Fourier transform IR spectroscopy has been used to study the oxidation kinetics of the biomolecular components of the eukaryotic cancerous HeLa cells initiated by the photogenerated charges on TiO₂. It was shown that the organic material of the cells on the porous film of the TiO₂ nanoparticles was mineralized in a such way that the TiO₂ surface was purified. The basic organic groups of Amide-I, Amide-II and phosphate were oxidized at different rates. Amide-II oxidized most rapidly, then followed Amide-I. The phosphate was the most resistant to oxidation.     

Fourier transform infrared study of orientation and relaxation in poly(methyl methacrylate)

Infrared measurements of the dicroic ratio of poly-(methyl methacrylate) absorption bands provide a valuable method for determining the orientation as well as the relaxation of chains during stretching. Different strain rates and temperatures of stretching were used. Orientation relaxation was determined and a master curve was obtained at a reference temperature T_O = 135°C. The master curve shows that orientation relaxation behaves similarly to mechanical relaxation.     

Fourier transform infrared study of mercury interaction with carboxyl groups in humic acids

An interaction between humic acid, an organic part of soil and mercury was studied by Fourier transform infrared spectroscopy (FTIR) and by ICP-AES analysis under given pH and concentration conditions. First the spectroscopic model was validated on the interaction of simple molecules representing the structural components of humic acid such as benzoic acid, catechol and salicylic acid with mercury. The interaction of carboxylic parts of humic acid with mercury is very interesting and easily characterised by infrared spectroscopy, an ideal mean for molecular study. Under the salt form (commercial humic acid Fluka TM: FHA), humic acid reacts with mercury in a different way from its acid form (FHA purified noted PFHA) and the Leonardite (LHA). Because of the straightforward exchange between Na⁺, Ca²⁺ and Hg²⁺, fixation of the latter is much more important with the salt form (FHA). However, this reaction is reduced under the acid form (PFHA, LHA) because the exchange with protons is difficult. The effect of this exchange was studied by FTIR showing the intensity decrease of ν_CO (COOH), the carboxylic functional group band of the acid, and the shifting of ν_as (COO⁻), the carboxylate functional group band under given pH and mercury conditions. For the FHA salt form, the characteristic band ν_CO (COOH) represented by a shoulder did not evolute, whereas the corresponding band to ν_as (COO⁻) strongly shifted (40 cm⁻¹) for a maximum Hg²⁺ concentration (1 g l⁻¹). On the other hand, for the acid form (PFHA, LHA), the intense band of ν_CO (COOH) disappeared proportionally to the increase of Hg²⁺concentration and the ν_as (COO⁻) band moved for about 20 cm⁻¹. The same results were reached with pH variations. Our results were confirmed by ICP-AES mercury analysis. This study shows that humic acids react differently according to their chemical and structural state.     

Fourier transform infrared emission spectra of MgH and MgD

High resolution Fourier transform infrared emission spectra of MgH and MgD have been recorded. The molecules were generated in an emission source that combines an electrical discharge with a high temperature furnace. Several vibration-rotation bands were observed for all six isotopomers in the X (2)Sigma(+) ground electronic state: v=1-->0 to 4-->3 for (24)MgH, v=1-->0 to 3-->2 for (25)MgH and (26)MgH, v=1-->0 to 5-->4 for (24)MgD, v=1-->0 to 4-->3 for (25)MgD and (26)MgD. The new data were combined with the previous ground state data, obtained from diode laser vibration-rotation measurements and pure rotation spectra, and spectroscopic constants were determined for the v=0 to 4 levels of (24)MgH and the v=0 to 5 levels of (24)MgD. In addition, Dunham constants and Born-Oppenheimer breakdown correction parameters were obtained in a combined fit of the six isotopomers. The equilibrium vibrational constants (omega(e)) for (24)MgH and (24)MgD were found to be 1492.776(7) cm(-1) and 1077.298(5) cm(-1), respectively, while the equilibrium rotational constants (B(e)) are 5.825 523(8) cm(-1) and 3.034 344(4) cm(-1). The associated equilibrium bond distances (r(e)) were determined to be 1.729 721(1) A for (24)MgH and 1.729 157(1) A for (24)MgD.     

Fourier transform infrared study of poly (2-hydroxyethyl methacrylate) PHEMA

 Fourier transform infrared spectra in the wave number range 450–4500 cm^-1 of poly (2-hydroxy-ethyl methacrylate) PHEMA have been studied as functions of water content in the range 38–2.6 wt% and of temperature in the range 300–373 K. The results show changes in the intensities of the stretching frequencies of the carbonyl band, H–O–H bending vibration and O–H stretching vibration with a change in water content and temperature. The results confirm two types of water in the hydrogel polymer system, tightly bound water and loosely bound water. At low concentrations, water is mainly hydrogen-bonded to the polymer and is described as tightly bound water. However, at water concentrations greater than 18% by weight, part of the water exists in a different form and behaves as loosely bound water. For concentrations over 30%, there is some evidence that excess water behaves more loosely bound somewhat like bulk water. Infrared spectroscopic results supplement those obtained by means of NMR by Smyth et al. and by dielectric spectroscopy. Our results also show that some of the water continues to be hydrogen bonded to the polymer until at least a temperature of 373 K when the bulk water should have evaporated. FTIR is found to yield greater site-specific insight into the local behaviour of water in hydrated PHEMA. Received: 22 August 1996 Accepted: 11 November 1996     

Fourier transform infrared study on the sorption of water to various kinds of polymer thin films

The state of sorbed water and the sorbing processes of water to various polymer thin films were studied with Fourier transform infrared (FTIR) spectroscopy. To prepare the polymer films, we used poly(ethylene glycol)s of different molecular weights and various kinds of vinyl polymers, such as poly(2‐methoxyethyl acrylate). The O? H stretching band of water sorbed in the films increased gradually on contact with water vapor at 50% relative humidity and leveled off. When O? H stretching bands of water sorbed to polymer films were compared, the peak positions and profiles of water sorbed to the polymeric materials with the same hydrogen‐bonding site were similar. A hybrid density‐functional method supported the assignment of the peaks. Furthermore, the diffusion coefficient (D) of water vapor in the polymer films was estimated by time‐resolved measurements of the sorbed water at the very initial stage (0–830 s). It was clearly shown that the D values of water vapor in the polymer materials with a strong hydrogen‐bonding site were smaller than those in hydrophobic polymers. The usefulness of the FTIR technique to investigate water sorption to polymer materials was definitely demonstrated. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2175–2182, 2001     

Fourier transform infrared analysis of the stereoregularity of atactic polystyrene

Fourier transform infrared spectroscopy provides a sensitive method allowing one to detect easily changes in the syndiotactic sequence content in polystyrene. The method is based on analysis of the 540-cm^?1 absorption band, which is conformationally sensitive. Results in the solid state and solution are presented. A shift of 2.5 cm^?1 of the 540-cm^?1 band towards the high-frequency side is observed between the solid state and solution.     

Nature of water in nacre: a 2D Fourier transform infrared spectroscopic study

In this work, the interactions of aragonite and organic matrix in nacre with water are investigated using two-dimensional (2D) Fourier transform infrared (FTIR) spectroscopy. The 2D-FTIR analysis revealed four bands in the OH stretching region at around 3550, 3445, 3272 and 3074 cm(-1). Two additional bands were found at around 3616 and 3282 cm(-1) after deconvolution of the nacre spectrum. The bands at around 3616 and 3550 cm(-1) are assigned to asymmetric and symmetric OH stretching of partially hydrogen bonded water molecules. The bands at around 3445 and 3272 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules fully hydrogen bonded with surrounding water molecules. Presence of above bands in the nacre spectrum suggests that water, in form of clusters, is present in protein matrix and aragonite pores. Water may also hydrogen bond with the organic matrix. The bands observed at 3282 and 3074 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules, chemisorbed on surfaces of aragonite platelets. Polarization experiments suggest that H-O-H plane of water molecules is along to c-axis of aragonite platelets.