A fourier-transform infrared spectroscopic study of the hydrolytic stability of silane coupling agents on E-glass fibers

Fourier-transform (FT) infrared spectroscopy has been applied to the study the hydrothermal degradation of various coupling agents on E-glass fibers. The coupling agents studied include γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, and cyclohexyltrimethoxysilane. The amount of coupling agents on E-fibers was measured as a function of immersion time in water at 80°C. Structural changes were also followed by obtaining FT-IR difference spectra of the coupling agent on the glass fiber surface. Silanes desorb quite differently depending on the organofunctional groups. The resistance to desorption is strongly influenced by the organization of the silane interphase as well as the solubility of the silane in water.     

Estimation of ester hydrolysis parameters by using fourier-transform infrared spectroscopy and the extended kalman filter

Fourier-transform (FTIR) spectroscopy has found a wide range of applications. Attempts have been made to make FTIR spectroscopy a reliable quantiative technique for obtaining chemical information foru complex systems, but it is often difficult to obtain even qualitative information about a complex system because of matrix, interaction, and background effects on the infrared on the spectra. In this study, FTIR spectroscopy was used in conjuction with the extended Kalaman filter, a recursive digital filter, to investigate the simple neutral hydrolysis of two esters in aqueous solutions. Interactions between the solvent, reactants and products of the hyrolysis perturb the spectrum, making a single-wavelength kinetic analysis impractical. With the extended Kalman filter, a range of frequencies where severe perturbation does not occur is processed to obtain not only the rate constant but also the initial reactant concentrations.     

Studies of alkoxysilane hydrolysis and condensation by fourier-transform infrared spectroscopy with a cylindrical internal-reflection cell

The relative concentrations of unhydrolyzed and hydrolyzed forms of (3-trimethoxysilyl) propyloctadecyldimethylammonium chloride (SiQAC) were determined in aqueous solutions as functions of pH and time. Subtraction of the concentrations of these two forms of SiQAC from the total concentration of SiQAC was assumed to give the concentration of the “condensed” form of SiQAC irrespective of its extent of oligomerization. The silane, SiQAC, is used to modify a variety of surfaces to impart antimicrobial properties. Knowledge of the speciation of SiQAC is required to understand its effect on the efficiency and durability of such chemically modified surfaces. The cylindrical internal- reflection/FTIR spectroscopy was also used to determine the rate constants for hydrolysis and condensation of monomethoxytrimethylsilane (MTMS) in 10% (v/v) water/acetone medium as a function of hydrogen-ion concentration. The hydrolysis of MTMS was found to be first order in both silane and water concentrations. the condensation of trimethylsilanol to form hexamthyldisiloxane was second order in silanol concentration.     

A spectroscopic study of the hydrolysis products of aryltellurium trihalides

The hydrolysis of aryltellurium trihalides to aryltellurium oxide halides in neutral aqueous media is considered to proceed in a stepwise manner in which the first stage involves the formation of a monomeric species. In alkaline media the initially isolated hydrolysis product analyses as (p-EtOC₆H₄)TeO(OH) and on treatment with dilute acid, affords the known (p-EtOC₆H₄TeO)₂O.The infrared spectra are assigned in the low frequency region for the compounds RTe(O)X (X = halogen), RTeO(OH) and (RTeO)₂O. It is argued that the probable coordination number for tellurium in RTe(O)X is four, and that a ring structure is likely. The preparation of the salts(C₅H₅NH⁺)(RTeCl₄^?) is reported and the anions are considered to have square-based pyramidal structures of approximately C_4v symmetry. The reaction of (C₅H₅NH⁺)(PhTeCl₄^?) with acetone affords Ph(CH₃COCH₂)TeCl₂.     

Matrix isolation infrared spectroscopic and theoretical study of the hydrolysis of boron dioxide in solid argon

The reaction of boron dioxide with water molecule has been studied using matrix isolation infrared spectroscopy. The boron dioxide molecules produced by codeposition of laser-evaporated boron atoms with dioxygen react spontaneously with water molecules to form OB(OH)2, which is characterized to have a doublet ground-state with two OH groups in the cis-trans form. Isotopic substitution results indicate that the hydrolysis process proceeds via a concerted two hydrogen atom transfer mechanism. The cis-trans-OB(OH)2 molecule is photosensitive; it decomposes to the OH x OB(OH) complex upon broadband UV-visible irradiation. The OH x OB(OH) complex is determined to have a (2)A' ground-state with a bent C(s) symmetry, in which the terminal oxygen atom of the OB(OH) fragment is hydrogen bonded with the hydroxyl radical. The OH x OB(OH) complex recombines to the cis-trans-OB(OH)2 molecule upon sample annealing.     

A thermogravimetric and infrared emission spectroscopic study of alunite

Thermogravimetric and differential thermogravimetric analysis has been used to characterize alunite of formula [K₂(Al³⁺)₆(SO₄)₄(OH)₁₂]. Thermal decomposition occurs in a series of steps (a) dehydration up to 225°C, (b) well defined dehydroxylation at 520°C and desulphation which takes place as a series of steps at 649, 685 and 744°C.The alunite minerals were further characterized by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3463 and 3449 cm^?1 are observed. At 550°C all intensity in these bands is lost in harmony with the thermal analysis results. OH stretching bands give calculated hydrogen bond distances of 2.90 and 2.84–7 Å. These hydrogen bond distances increase with increasing temperature. Characteristic (SO₄)^2? stretching modes are observed at 1029.5, 1086 and 1170 cm^?1. These bands shift to lower wavenumbers on thermal treatment. The intensity in these bands is lost by 550°C.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Hydrated double carbonates – A Raman and infrared spectroscopic study

The Raman spectra of selected double carbonates including pirssonite, gaylussite, shortite and quintinite complemented with infrared spectra have been used to characterise the structure of these carbonate minerals. By using a Libowitzky type function hydrogen bond distances for these minerals of 2.669–2.766 Å are estimated. The variation in the hydrogen bond distances contributed to the stability of the mineral. The Raman spectrum of pirssonite shows a single band at 1080 cm⁻¹ attributed to the (CO₃)²⁻ symmetric stretching mode, in contrast to shortite and quintinite where two bands are observed. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of pirssonite and gaylussite.     

A new sampling technique for reversed-phase liquid chromatography/fourier-transform infrared spectrometry

A systematic study of the utility of stainless-steel wire nets (SSWN) as a substrate for infrared sampling is described. The nets can be used with polar solvents including water, as well as non-polar solvents, without harming the surface. The use of the SSWN simplifies interfacing between a reversed-phase liquid chromatograph (l.c.) and a Fourier-transform infrared spectrometer. It is used as a l.c. detector cell by collecting the effluent from l.c. on the cell itself. The technique is tested extensively with carbaryl as sample and is applied successfully to the detection of a pharmaceutical mixture (phenacetin, caffeine and aspirin) separated by reversed-phase l.c. with a (3:2, v/v) methamol/water mobile phase.     

The effect of particle size on fourier-transform infrared photoacoustic spectra

The effect of particle size on infrared photoacoustic spectra has been investigated by use of naturally occurring quartz. It is observed that the PAS peak intensities increase with a decrease in particle diameter and that the peak intensity ratios are not constant for particles of different diameters. When the particle diameter becomes smaller than the thermal diffusion length for a specific peak, a more dramatic increase in peak intensity is observed. It is also found that the PAS peak shape deteriorates with an increase in particle diameter. The effect of optical velocity of the interferometer on PAS peak intensities is also reported.     

An infrared and Raman spectroscopic study of the uranyl micas

Vibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or 1/2(HAl) and X is As or P. Included in these minerals are autunite, metautunite, torbernite, meta-torbernite, meta-zeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm(-1), attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation.     

The characterization of polymer deformation by rheo-optical fourier-transform infrared spectroscopy

The mechanical properties of polymeric materials are of considerable importance to their engineering applications. Apart from the chemical structure and the thermal history, molecular orientation has a major influence on the mechanical properties of a polymer. The increased need for more detailed data and a better understanding of the mechanisms involved in polymer deformation has led to the search for new experimental techniques to characterize transient structural changes during mechanical processes. With the advent of rapid-scanning Fourier - transform infrared (FTIR) spectroscopy, simultaneous vibrational spectroscopic and mechanical (so-called rheo-optical) measurements during the deformation of polymers have emerged as a very informative probe for the study of deformation and relaxation phenomena in polymer films in the late seventies and have since then been applied to obtain data on strain-induced crystallization and orientational and conformational changes during mechanical treatment of a wide variety of polymers.     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.     

A fourier transform infrared spectroscopic study of the molecular interaction in synthetic bilayer membrane

Fourier transform infrared spectroscopy is used to study the molecular interaction between gramicidin D and bilayer membranes, dioctadecadimethylammonium bromide (2C₁₈N⁺2C₁Br⁻), and 1,2-di-palmytoyl- -α-phosphatidylcholine (DPPC). Frequencies and bandwidths of the symmetric CH₂ stretching band measured as a function of temperature are used to study variation of packing of alkyl chains. The bilayer membrane prepared from 2C₁₈N⁺2C₁Br⁻ is found to have a gel to liquid crystal phase transition at 42°C. The presence of gramicidin in the membrane causes an increase in the mobility of the alkyl chain and also a decrease in the abruptness of the transition.The frequencies of amide I and II bands of gramicidin reflecting secondary structures of polypeptides are used to identify its conformation in membranes and to study the interaction between gramicidin and the matrices. Gramicidin is found to have hydrophobic interaction with 2C₁₈N⁺2C₁Br⁻, whereas it has both hydrophobic and hydrophilic interactions with DPPC.     

Coordination behaviour of nicotinamide: an infrared spectroscopic study

A series of Hofmann-type complexes containing two nicotinamide(nia) molecules attached to transition metal (II) (M) tetracyanonickelate frame with the formula: M(nia)₂Ni(CN)₄ (where M=Mn, Co, Ni, Cu or Cd) have been synthesised for the first time. Metal (II) halide complexes of nicotinamide complexes of the type [M(nia)₂X₂ (M=Cd, Ni, Cu, Hg; X=Cl, Br) and Ni(nia)₄Br₂ nia=nicotinamide] have also synthesised. The FTIR spectra are reported in the 4000-400 cm⁻¹ region. Vibrational assignments are given for all the observed bands. The analysis of the vibrational spectra indicates that there are some structure-spectra correlations. A pronounced change was observed in the N-H stretching frequencies of the NH₂ group. It is proposed that the amide NH₂ group influence by the intramolecular hydrogen bond in the complexes. The coordination effect on the nicotinamide modes is analysed.     

Adsorption of 2-chloropyridine on oxides--an infrared spectroscopic study

The adsorption of 2-chloropyridine on SiO(2), TiO(2), ZrO(2), SiO(2)-Al(2)O(3) and H-mordenite has been studied by IR spectroscopy. The different modes of interaction with oxide surfaces, i.e. hydrogen-bonding and adsorption at Br?nsted or Lewis acid sites, was modelled by ab initio calculations at the B3LYP/DZ+(d) level. Adsorption on SiO(2) results in hydrogen bonding to surface hydroxyl groups, whereas the spectra obtained following adsorption on TiO(2) and ZrO(2) display evidence for electron transfer at Lewis acidic surface sites. Protonation of 2-chloropyridine at Br?nsted acidic sites was detected only for adsorption on SiO(2)-Al(2)O(3) and H-mordenite, indicating the presence of Br?nsted acidic sites on these oxide surfaces with pK(a) values 相似文献