Far-infrared studies of ion clustering in ionomers

The far-infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion-site concentration to obtain spectroscopic evidence of domain formation. A far-infrared band, due to the vibration of a higher-order cluster, is found at 170 cm^?1in Na⁺-form PSMA. This band, which is observed in addition to the known cation-motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggregation models.     

Infrared spectroscopic properties of sodium bromide aerosols

The infrared extinction spectra of aqueous NaBr aerosols at ambient temperature have been measured as a function of relative humidity. Submicron-sized aerosol particles atomized from aqueous NaBr solutions at various concentrations are dried and/or mixed with nitrogen at different humidities and spectroscopically monitored as they flow through an infrared absorption cell. Estimated dry particle median diameters range from 0.24 to 0.15 microm, as calculated from Mie extinction theory. Measured deliquescence and efflorescence relative humidities (35-40% and 25-30%, respectively) are in accordance with previously reported ones. Our results show that NaBr particles take up water only moderately over the deliquescence point, with a significant increase at relative humidities above 70%. The effect of particle size onto water uptake properties has been studied, indicating that smaller particles take up lower amounts of water, and only increase their size significantly at relative humidities near saturation. Particle composition and diameter growth factors have been calculated from spectral data and are shown to be consistent with those predicted from thermodynamic data and Kohler theory. Band centers of liquid water in NaBr aerosols relative to pure water are blue-shifted up to 50 cm-1 at low humidities. Particle structure and phase, together with atmospheric implications, are also discussed.     

Infrared spectroscopic studies of substituted 1,2-diphenylcyclopropenes

For the investigation of the character of a substituent at position 3 of the ring and the double bond, i.r. spectra of substituted 1,2-diphenilcyclopropenes were studied. Frequencies and integral intensities of the double bond stretching vibration band were determined. It was proved that changes of the band's parameters caused by intermolecular interactions are substantially smaller than effects observed by changing the substituent. On the basis of correlation between changes of intensities of the ν_CC band and resonance constants of substituents and the character of the frequency dependence, a conclusion was reached on the resonance interactions of the substituent with σ_Walsh —MO of the cycle.     

纳米尺寸氧化铝的红外光谱研究

用改进的溶胶-凝胶法制备了均一粒径的纳米尺寸Al~2O~3样品,在相同仪器条件下测得红外光谱。研究了烧结温度、反应物前驱体的pH值和分散介质对IR谱的影响。结果表明,纳米氧化铝IR谱的峰值、强度和带宽有规律变化与制备因素、颗粒尺寸及结构有关。当粒径变小处于表面的原子数增多时,与Al~2O~3纵向声子跃迁有关的谱带强度有增强趋势。     

Infrared spectroscopic studies of dihydrogen adsorbed on oxide surfaces

The complex structure of the IR spectra of dihydrogen adsorbed at 60–77 K on several oxide adsorbents, in the 4300–4000 cm^–1 region, is supposed to be due to the combination of ^v H-H with a low-frequency vibration of the H₂ molecule with respect to the surface.

---

4300–4000 ^–1 - H₂, 60–77 . , ^v H-H .

     

Infrared spectroscopic studies on interactions in trifluoroacetic acid-sulfur dioxide systems

The method of frustrated multiple internal reflection (FMIR) infrared spectroscopy was used to study the nature of intermediates that formed upon oxidation of sulfur dioxide in trifluoroacetic acid (TFA) of various concentrations at 30°C. It was established that sulfur dioxide bound to a complex with TFA is oxidized by dissolved oxygen in systems that contain 99.9 and 55.5% trifluoroacetic acid.     

Infrared spectroscopic study of thermal transitions in poly(methyl methacrylate)

The ester CD₃ stretching modes in a partially deuterated poly(methyl methacrylate) sample have been studied as a function of temperature and bands in the CD stretching region assigned to fundamentals in Fermi resonance with overtone/combination modes. Changes in band parameters (widths, shapes) are observed at specific temperatures. Time correlation functions and their variation with temperature were calculated for the most intense modes observed in this region of the spectrum. The correlation functions were modeled by assuming that there is a fast relaxation process characterized by a single relaxation time that is inhomogeneously broadened by a slower process, also characterized by a single relaxation time. The fast modulation is in the sub picosecond time range, while the slower process has a relaxation time of the order of 1-10 ps. Relaxation times and other parameters are sensitive to transitions observed both below and above the glass transition, as well as at the T_g itself. The high temperature transition corresponds to a liquid-liquid transition observed in other studies and predicted by theory. The lower temperature transition appears to correspond to the Vogel-Fulcher or Kauzmann temperature. Infrared spectroscopy and band shape analysis appear to be a useful probe of these transitions.     

Infrared spectroscopic studies of hydrogen-bonded complexes in cryogenic sulutions

We have measured the ν_s(OH) band parameters of the IR absorption spectra for a wide variety of hydrogen-bonded (HB) complexes of CH₃OH(D), CF₃CH₂OH, and (CF₃)₃COH(D) with some simplest representatives of various classes of bases in Xe and Kr in the temperature range 120–270 K. The ν_s(OH) absorption bands of the HB complexes in solution in atomic solvents have been demonstrated to be narrower by a factor of 2 to 4 than in molecular solvents at the same temperature. The fact that the ν_s(OH) bandwidths in Xe and in the gas phase at similar temperatures are practically the same indicates that these bandwidths are in both cases governed mainly by the contribution of “hot transitions” from a sequence of excited levels of the ν_β low-frequency bending mode of the hydrogen bond. The other characteristic features revealed for the complexes under study in liquid Xe and Kr at ν_s(OH) frequency shifts up to 500 cm⁻¹ include: (1) slight temperature dependence of the ν_s(OH) bandwidth (0.1–0.3 cm⁻¹/K), (2) almost “normal” isotope frequency ratio ν_s(OH)/ν_s(OD) (1.34–1.36) and (3) low ν_s(OH) temperature shift values (0.1–0.4 cm⁻¹/K).     

Multiple glass transitions and local composition effects on polymer solvent mixtures

Recent differential scanning calorimetry (DSC) results on polystyrene–solvent mixtures show two distinct glass transitions whose positions and widths vary with composition. Parallel work on the dynamic response in polymer blends has focused on how segmental mobilities are controlled by local composition variations within a “cooperative volume” containing the segment. Such variations arise from both chain connectivity and composition fluctuations. We account for both using a lattice model for polymer–solvent mixtures that yields the composition distribution around polymer and solvent segments. Insights from our lattice model lead us to simplified calculations of the mean and variance of local composition, both in good agreement with lattice results. Applying our model to compute DSC traces leads to an estimate of the cooperative volume, since a larger cooperative volume both reduces the biasing effect of connectivity, and narrows the composition distribution. Comparing our results to data, we are able to account for the composition-dependent broadening with a cooperative length scale of about 2.5 nm. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3528–3545, 2006     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.     

Infrared spectroscopic studies on metal cyanides adsorbed on inorganic support materials

The adsorption of CuCN and KCN onto the surface of inorganic support materials such as silica gel, alumina and charcoal can be conveniently studied by i.r. spectroscopy. The type of support material can have a profound effect on the nature of the adsorbed cyanide.     

Infrared spectroscopic studies of free-base tetraphenylporphine and its dication

We present here the infrared absorption spectra of free-base tetraphenylporphine and its dication. Most of the allowed IR bands of porphyrin skeletal are observed in pairs due to two-fold symmetry of the free-base tetraphenylporphine. Observation of some new bands, disappearance of few bands in the IR spectrum of dication are interpreted on the basis of point group symmetry S4. Intensity change in the observed bands due to vibrational motion of the phenyl rings for dication is also explained on the basis of symmetry of dication. Sharing of electrons of the B(1u) orbitals by the two added protons are responsible for the shifts in the position of certain IR bands for dication.     

Effects of diluent on molecular motion and glass transitions in polymers. III. The system poly(vinyl acetate)–toluene

Dielectric measurements, differential thermal analyses (DTA), and broad-line proton magnetic resonance (NMR) measurements are reported on the system poly(vinyl acetate)–toluene. Four dielectric relaxations were observed between 80 and 400°K. From proton NMR measurements on solutions in toluene and in deuterated toluene, the relaxation processes can be assigned, respectively, to segmental motion of poly(vinyl acetate), α; motion of side group, β′ rotation of toluene, β; local motions of poly(vinyl acetate) and toluene, γ, in order of appearance with decreasing temperature. Two stepwise changes in DTA traces have been observed and can be assigned as glass transition points T_gI and T_gII. Comparison of these glass transition points with temperatures at which dielectric relaxation times for the α and β processes are 100 sec, indicate that segmental motion of poly(vinyl acetate) and rotation of toluene are frozen-in at T_gI and T_gII, respectively. Activation plots for the α process conform to the Vogel–Tamman equation. In terms of the parameters A, B, and T₀ of the equation, T_gI can be represented by an expression of the form T_gI ≈ T₀ + B/(A + 3). In the range of concentration above 50% by weight, A and B are almost independent of concentration but T₀ varies strongly. The nature of the secondary dispersions is also discussed.     

Thermal and spectroscopic studies of sodium and light lanthanide (III) complexes with 2,4-pyridinedicarboxylate anion

Pyridine-2,4-dicarboxylic acid (lutidinic acid) is next one after pyridine-2,5-dicarboxylic acid of the six isomers which lanthanide complexes were studied thermally and spectrally. New complexes synthesized with light lanthanides (III) with general formula Ln₂L₃·nH₂O, where n?=?7.5; 8; 8.5; 9, were obtained. Sodium salt was obtained as hexahydrated compound. Hydrated complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), and Gd(III) are thermally stable up to 303?C313?K. Dehydration process run for all compounds in one stage, anhydrous compounds decompose through appropriate light lanthanides (III) oxalates, oxocarbonates, carbonates to metal oxides. Theoretical IR and Raman studies were carried out in order to identify precisely characteristic group bands vibrations present on IR and Raman spectra.     

Infrared spectroscopic studies of the acidity of chromium molybdate catalysts

NH₃ adsorption on chromium molybdate at 25 and 350°C has been studied. Ammonia chemisorption has been found on electron-acceptor and Brønsted centers. The acceptor capacity of cations is shown to change as compared to individual oxides and upon high-temperature interaction with ammonia.

---

NH₃ 25° 350°. . .

     

Infrared studies of cryogenic transitions in poly(ethylene terephthalate)

Measurements of infrared absorbance as a function of temperature down to 77°K have been made on poly(ethylene terephthalate). Transitions observed by other techniques such as torsion pendulum measurements are reflected in the infrared measurements by an abrupt change in the slope of the absorbance versus temperature. The infrared measurements are made on bands of known structural origin so the structures contributing to each transition can be determined. The β transition is shown by infrared to be a composite of two peaks with the lower-temperature portion arising from the amorphous regions and the higher-temperature portion from the crystalline regions.     

Infrared spectroscopic studies of siderophore-related hydroxamic acid ligands adsorbed on titanium dioxide

The adhesion of bacteria to metal oxide and other mineral surfaces may involve bacterial siderophores, many of which contain hydroxamic acid (Ha) ligands. The adsorption behavior of the siderophore-related ligands acetohydroxamic acid, N-methylformohydroxamic acid, N-methylacetohydroxamic acid, and 1-hydroxy-2-piperidone on titanium dioxide thin films has been investigated using in situ ATR-IR spectroscopy with variation of concentration and pH. All the ligands were found to adsorb strongly on the TiO2 surface as hydroxamate ions and form bidentate surface complexes. Vibrational modes involving C=O stretching and N-O stretching of these ligands were assigned by comparing observed IR spectra with those calculated by the density functional method at the B3LYP/6-31+G(d) level. Calculated spectra of the complex [Ti(Ha)(OH)4]-, used to model the TiO2 surface, were compared with observed spectra of adsorbed hydroxamic acids. These results suggest that hydroxamic acid ligands in siderophores would be expected to bind to metal (oxide) and mineral surfaces during bacterial adhesion processes.