Showing papers on "Fourier transform infrared spectroscopy published in 2001"

Thermal Degradation Chemistry of Alkyl Quaternary Ammonium Montmorillonite

Abstract: The thermal stability of organically modified layered silicate (OLS) plays a key role in the synthesis and processing of polymer-layered silicate (PLS) nanocomposites. The nonoxidative thermal degradation of montmorillonite and alkyl quaternary ammonium-modified montmorillonite were examined using conventional and high-resolution TGA combined with Fourier transform infrared spectroscopy and mass spectrometry (TG−FTIR−MS) and pyrolysis/GC−MS. The onset temperature of decomposition of these OLSs was approximately 155 °C via TGA and 180 °C via TGA−MS, where TGA−MS enables the differentiation of water desorbtion from true organic decomposition. Analysis of products (GC−MS) indicates that the initial degradation of the surfactant in the OLS follows a Hoffmann elimination reaction and that the architecture (trimethyl or dimethyl), chain length, surfactant mixture, exchanged ratio, or preconditioning (washing) does not alter the initial onset temperatures. Catalytic sites on the aluminosilicate layer reduce ther...

XPS and FTIR Surface Characterization of TiO2 Particles Used in Polymer Encapsulation

Abstract: The surfaces of hydrophilic (P25) and hydrophobic (T805) TiO2 particles were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to gain a better understanding of the adsorption mechanism of OLOA 370 (polybutene-succinimide pentamine) on TiO2 particles dispersed in styrene monomer prior to miniemulsion encapsulation polymerizations. XPS analysis revealed that both the P25 and T805 TiO2 particles had significant amounts of hydroxyl groups on their surfaces. The XPS results showed that the surface hydroxyl concentration on the hydrophilic (P25) particles was 3.3 OH/nm2, whereas the trimethoxy octyl silane (TMOS)-surface-modified hydrophobic (T805) particles unexpectedly contained 6.6 OH/nm2. This apparent increase in the hydroxyls was attributed to hydrolysis of −OCH3 on the TMOS. The majority of these groups, however, were apparently either not acidic or not accessible to the OLOA 370 in adsorption studies, where the concentration of reactive hydroxyls...

Pepsin-gold colloid conjugates: preparation, characterization, and enzymatic activity

Abstract: Pepsin−colloidal gold conjugates were prepared by a simple protein-friendly process and the enzymatic activity of the bioconjugates is reported. The pepsin−gold conjugates are obtained by mixing colloidal gold and protein solutions at pH = 3 and, thereafter, centrifugation, washing, and redispersion of the pepsin−gold conjugate material in water. The bioconjugates in solution were characterized by UV−vis spectroscopy, fluorescence spectroscopy, and biocatalytic activity measurements while films of the bioconjugate material obtained by solvent evaporation on suitable substrates were further analyzed by scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), transmission electron spectroscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). While TEM and SEM measurements showed aggregates of the enzyme/colloidal gold conjugates, the intactness of secondary and tertiary structures of the enzyme, as determined by FTIR and fluorescence s...

Highly bioactive P2O5–Na2O–CaO–SiO2 glass-ceramics

Abstract: Glasses having a chemical composition between 1Na2O–2CaO–3SiO2 (1N2C3S) and 1.5Na2O–1.5CaO–3SiO2, containing 0, 2, 4 and 6 wt% P2O5, were crystallized to several volume percent through thermal treatments in the range 550–700 °C. These glasses and glass-ceramics were exposed to a simulated body fluid solution (SBF-K9 which is close to human plasma) for several time periods. Fourier transform infrared spectroscopy (FTIR) was used to determine the rate of hydroxy carbonate apatite (HCA) formation. Crystallization decreased the kinetics but did not inhibit the development of a HCA layer, even in fully crystallized ceramics. The onset time for crystallization of HCA varied from 8 h for a glass containing 6% P2O5 to 35 h for a fully crystallized 1.07Na2O–2CaO–3SiO2 ceramic. The HCA layer formation of these compositions in `in vitro' tests is much faster than in commercial bioactive materials such as synthetic hydroxyapatite ceramic, A/W glass-ceramic, Ceravital and Bioverit, for which the onset time usually takes at least seven days. FTIR and inductive coupled plasma studies confirmed the formation of an apatite layer which indicates bioactivity in the 1N2C3S crystal phase. X-ray diffraction experiments show that the phosphorus ions are kept in solid solution in the crystal phase. An apatite-like compound only appeared when the specimens were submitted to very long additional thermal treatments. The bioactivity of commercial materials is based on the apatite crystal phase, while the high level of bioactivity of this new generation of glass-ceramics is attained due to the combination of two mechanisms acting simultaneously; a non-phosphate bioactive crystal phase (1N2C3S) and the phosphorus ions in solid solution which are easily released from the structure, promoting a faster HCA layer formation similar to 45S5 Bioglass®.

Materials characterization of ZrO2–SiO2 and HfO2–SiO2 binary oxides deposited by chemical solution deposition

Abstract: The thermal stability, microstructure, and electrical properties of xZrO2⋅(100−x)SiO2 (ZSO) and xHfO2⋅(100−x)SiO2 (HSO) (x=15%, 25%, 50%, and 75%) binary oxides were evaluated to help assess their suitability as a replacement for silicon dioxide gate dielectrics in complementary metal–oxide–semiconductor transistors. The films were prepared by chemical solution deposition using a solution prepared from a mixture of zirconium, hafnium, and silicon butoxyethoxides dissolved in butoxyethanol. The films were spun onto SiOxNy coated Si wafers and furnace annealed at temperatures from 500 to 1200 °C in oxygen for 30–60 min. The microstructure and electrical properties of ZSO and HSO films were examined as a function of the Zr/Si and Hf/Si ratio and annealing temperature. The films were characterized by x-ray diffraction, mid- and far-Fourier transform infrared (FTIR), Rutherford backscattering spectroscopy, and Auger electron spectroscopy. At ZrO2 or HfO2 concentrations ⩾50%, phase separation and crystallizatio...

FTIR AND DSC STUDIES OF MECHANICALLY DEFORMED β-PVDF FILMS

Abstract: Films of semicrystalline poly(vinylidene fluoride) (PVDF) in the β-phase were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The main goal of this study was to improve the understanding of the structural changes that occur in β-PVDF during a mechanical deformation process. FTIR spectroscopy was used to examine the structural variations as a function of strain. DSC data allowed measurement of the melting temperatures and enthalpies of the material before and after deformation, providing information about the changes in the crystalline fraction. After the molecular vibrations were assigned to the corresponding vibrational modes, we investigated the energy and intensity variations of these vibrations at different deformations. A reorientation of the chains from perpendicular to parallel to the stress direction was observed to occur in the plastic region. During the deformation, a decrease in the degree of crystallinity of the material was observed, but ...

Porous Silicon as a Versatile Platform for Laser Desorption/Ionization Mass Spectrometry

Abstract: Desorption/ionization on porous silicon mass spectrometry (DIOS-MS) is a novel method for generating and analyzing gas-phase ions that employs direct laser vaporization. The structure and physicochemical properties of the porous silicon surfaces are crucial to DIOS-MS performance and are controlled by the selection of silicon and the electrochemical etching conditions. Porous silicon generation and DIOS signals were examined as a function of silicon crystal orientation, resistivity, etching solution, etching current density, etching time, and irradiation. Pre- and postetching conditions were also examined for their effect on DIOS signal as were chemical modifications to examine stability with respect to surface oxidation. Pore size and other physical characteristics were examined by scanning electron microscopy and Fourier transform infrared spectroscopy, and correlated with DIOS-MS signal. Porous silicon surfaces optimized for DIOS response were examined for their applicability to quantitative analysis, ...

Preparation, characterization and photocatalytic activity of polycrystalline zno/tio2 systems. 2. surface, bulk characterization, 4-nitrophenol photodegradation in liquid–solid regime

Abstract: Electron spin resonance spectroscopy (ESR), Fourier transform infrared spectroscopy (FTIR), and monitoring of pyridine (py) and boric acid trimethyl ester (BATE) adsorption for determining surface acidity and basicity, respectively, were used to carry out further characterization of mixed ZnO/TiO2 polycrystalline solids prepared by different methods. Moreover, the powders were tested in a batch photoreactor for a probe reaction, i.e., 4-nitrophenol photodegradation in aqueous medium. ESR results indicated the presence of signals attributable to Zn+ species in ZnO/TiO2 (anatase) solids, while in ZnO/TiO2 (rutile) samples the presence of zinc induced only the formation of signals probably due to Ti3+ centers. FT-IR spectra showed no significant differences of the surface hydroxylation degree of the various photocatalysts, whereas the surface acidic properties generally decrease by increasing the amount of ZnO. Coupling of ZnO and TiO2 semiconducting powders was not so beneficial, as expected on the basis of...

The defect structure of sol–gel-derived silica/polytetrahydrofuran hybrid films by FTIR

Abstract: The structural perturbations induced by polytetrahydrofuran (PTHF) on sol–gel hybrid films were identified by Fourier-transform infrared (FTIR) spectroscopy. The films were prepared by spin-coating, from aged solutions containing tetraethylorthosilicate (TEOS) as the inorganic precursor and different concentrations of PTHF. All the spectra reveal a set of bands that may be associated with structural defects of the silica network. The hybrid films show an additional `defect' band at 560 cm −1 , assigned to a skeletal vibration of 4-fold siloxane rings, whose intensity grows as the polymer content or molecular weight increases. The relative intensity of two components of the νasSi–O–Si mode (resolved by deconvolution of the band at ∼ 1080 cm −1 ) grow accordingly. They were thus assigned to the longitudinal (LO) and transverse optical (TO) modes of that vibration in 4-fold siloxane rings. Simultaneously, the bands assigned to the νSi–O− mode and to the νSi–O(H) mode of unreacted silanol groups (obtained by deconvolution of the band at ∼ 950 cm −1 ) increase. These conjugated observations lead to the conclusion that the polymer hinders the condensation reactions, being responsible for a more porous structure, with retention of a larger proportion of 4-fold siloxane rings. For high concentrations of high molecular weight PTHF, the defect structure of the films indicates that a partial segregation of the polymer occurs.

Nanosphere−Microsphere Assembly: Methods for Core−Shell Materials Preparation

Abstract: Core−shell composite materials consisting of a silica core and a polystyrene (PS) shell were prepared by colloidal assembly of PS nanospheres onto silica microspheres. The assembly process was controlled by specific chemical (amine−aldehyde) or biochemical (avidin−biotin) interactions between the nanospheres and microspheres. Colloidal assembly was performed using polymer nanoparticles (100−200 nm diameter) and silica particles (3−10 μm diameter). Heating the assembled materials to temperatures above the glass transition (Tg) of the polymer nanoparticles allows the polymer to flow over the microsphere surfaces, resulting in uniform core−shell materials. Nanosphere packing density on the microsphere surfaces influenced the uniformity of the resulting polymer shell. Scanning electron microscopy, transmission electron microscopy, scanning force microscopy, and Fourier transform infrared spectroscopy were used to characterize the materials presented in this paper.

Surface characterization of esterified cellulosic fibers by XPS and FTIR Spectroscopy

Abstract: X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy techniques were used to study the surface chemical compositions of cellulosic fibers before and after treatments. The fibers were treated with phthalic anhydride and maleated polypropylene for surface modifications. Both XPS and FTIR spectroscopy analysis indicated that chemical bonds between hydroxyl groups of cellulosic fibers and anhydride moieties of phthalic anhydride and maleated polypropylene have occurred through esterification reaction. These chemical reagents have been added to the surface of cellulosic fibers in the form of monoester, i.e., the formation of esterified cellulosic fibers bearing a pendent carboxylic group.

Changes in the Hydration States of Poly(N-alkylacrylamide)s during Their Phase Transitions in Water Observed by FTIR Spectroscopy†

Abstract: Phase transitions of poly(N-n-propylacrylamide) (PnPA), poly(N-isopropylacrylamide) (PiPA), and poly(N-cyclopropylacrylamide) (PcPA) in H2O and D2O were investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of these solutions were measured as a function of temperature (T) both in the heating and cooling processes. Subtraction of a spectrum at starting temperature (T0) from a spectrum at T gives an IR difference spectrum (ΔAT-T0). The magnitudes of ΔAT-T0 for IR absorption bands attributable to the alkyl and amide groups of these polymers critically increased at their lower critical solution temperatures (LCSTs). Redshifts of the amide II, C−H stretching, and C−H deformation bands were observed during the coil-to-globule transitions of these polymers. The amide I‘ bands of N-deuterated amide groups (−COND−) in PnPA and PiPA measured below their LCSTs could be fitted with single Gaussian components centered at 1630 and 1625 cm-1, respectively. In contrast, two components were observed i...

Enzyme-induced biodegradation of polycarbonate-polyurethanes: dependence on hard-segment chemistry.

Abstract: Polycarbonate urethanes (PCNUs) have been used as a replacement for traditional biomedical polyether-urethanes due to their reported resistance to oxidative biodegradation. However, relatively little is known about their hydrolytic stability in the presence of inflammatory derived enzymes. This has in part motivated the current study relating to the effect of hard segment chemistry and the microdomain structures generated by such chemistry, on the cholesterol esterase (CE) catalyzed hydrolysis of PCNUs. The bulk structures of the studied materials were characterized using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR) for their bulk structures, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for their subsurface structures. 14C-labeled PCNUs were incubated with CE (400 units/mL), for a period of 10 weeks (pH 7.0 at 37 degrees C), and radiolabel release was used to monitor the degradation. The results showed that all of the polymers synthesized in this study were susceptible to CE-catalyzed hydrolytic degradation, and that the extent of degradation was highly dependent on the nature of hard segment interactions within the polymer and at the surface. More specifically, the degree of phase separation and soft segment crystallinity were found to be less important in comparison to the hydrogen bonding among the carbonate and urethane linkages. The rank of the different chemical groups' susceptibility to hydrolysis was as follows: nonhydrogen bonded carbonate > nonhydrogen bonded urethane > hydrogen bonded carbonate > hydrogen bonded urethane. The findings suggest that the degree of hydrogen bonding, when processed into a polyurethane material could be an important parameter to consider in the design of new biostable polyurethane products.

Application of atmospheric pressure dielectric barrier discharges in deposition, cleaning and activation.

Abstract: Dielectric barrier discharges (DBDs) at atmospheric pressure are obtained using mixtures of He and Ar as carrier gasses and various reactive additives such as hydrocarbons, hydrogen and nitrogen. These DBDs are used in three applications: deposition of polymer films; cleaning of Ag and Cu substrates; and activation of polyurethane and steel surfaces. In the case of the film deposition, several process conditions are investigated and the resulting films are analysed by scanning electron microscope, Fourier transform infrared spectroscopy and NMR. In another series of experiments Ag and Cu surfaces, covered with sulfide and oxide layers, are treated by means of a DBD in helium or argon with hydrogen added. The surfaces are analysed with X-ray photoelectron spectroscopy. Finally, a He–N2 plasma is used as an activator of polyurethane.

Silicon Surfaces as Electron Acceptors: Dative Bonding of Amines with Si(001) and Si(111) Surfaces

Abstract: The bonding of the trimethylamine (TMA) and dimethylamine (DMA) with crystalline silicon surfaces has been investigated using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and density-functional computational methods. XPS spectra show that TMA forms stable dative-bonded adducts on both Si(001) and Si(111) surfaces that are characterized by very high N(1s) binding energies of 402.2 eV on Si(001) and 402.4 eV on Si(111). The highly ionic nature of these adducts is further evidenced by comparison with other charge-transfer complexes and through computational chemistry studies. The ability to form these highly ionic charge-transfer complexes between TMA and silicon surfaces stems from the ability to delocalize the donated electron density between different types of chemically distinct atoms within the surface unit cells. Corresponding studies of DMA on Si(001) show only dissociative adsorption via cleavage of the N−H bond. These results show that the unique geometric structu...

Stabilizing Effects of Various Polyelectrolyte Multilayer Films on the Structure of Adsorbed/Embedded Fibrinogen Molecules: An ATR-FTIR Study †

Abstract: The structural changes in fibrinogen as a consequence of its adsorption onto the surface of or its embedding into the interior of poly(allylamine hydrochloride) (PAH) or poly(styrenesulfonate) (PSS) multilayers are investigated by means of attenuated total reflection Fourier transform infrared (ATR−FTIR) spectroscopy. It is found that both adsorption and embedding preserve the secondary structure of the fibrinogen molecules. Furthermore, the interactions of the polyelectrolytes with the protein molecules prevent their aggregation, especially in the embedded state, at room temperature. Thus, it seems that the structure and the biological activity of proteins adsorbed on or embedded in polyelectrolyte multilayers could largely be preserved, which opens up great perspectives in the design of new bioactive surfaces. The nature and the extent of the polyelectrolyte−protein interactions are further studied via analysis of the thermotropic responses of the different architectures. It is found that both PAH- and ...

Soft Chemistry Synthesis and Characterization of Layered Li1-xNi1-yCoyO2-δ (0 ≤ x ≤ 1 and 0 ≤ y ≤ 1)

Abstract: Li1-xNi1-yCoyO2-δ oxides have been synthesized for 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1 by chemically extracting lithium at ambient temperature from LiNi1-yCoyO2 with an oxidizing agent NO2PF6 in acetonitrile medium. The samples have been characterized by X-ray diffraction, wet-chemical analyses to determine lithium and oxygen contents, and infrared spectroscopy. While the nickel-rich end members Ni1-yCoyO2-δ have the O3 structure similar to the initial LiNiO2, but with smaller lattice parameters, the cobalt-rich end members Ni1-yCoyO2-δ consist of a mixture of P3 and O1 phases that are formed from the initial O3 structure of LiCoO2 by a sliding of the oxide-ion layers. The nickel-rich phases Li1-xNi1-yCoyO2-δ have an oxygen content close to 2 with a negligible amount of oxygen vacancies, while the cobalt-rich phases have considerable amount of oxygen vacancies (δ = 0.33 in CoO2-δ). Fourier transform infrared spectroscopy indicates a semiconductor to metal transition in Li1-xCoO2-δ for (1 − x) < 0.77. On the other han...

Estimation of Hydrogen Bond Distribution in Coal through the Analysis of OH Stretching Bands in Diffuse Reflectance Infrared Spectrum Measured by in-Situ Technique

Abstract: A new method was presented to estimate the strength distribution of hydrogen bonds in coal. The hydrogen bonds include the coal intramolecule hydrogen bonds and coal−water hydrogen bonds formed by hydroxyls in coal. The method analyzes the FTIR spectrum ranging from 2400 to 3700 cm-1 obtained using the in-situ diffuse reflectance IR Fourier transform (DRIFT) technique with neat, undiluted, coal samples. The FTIR spectra during the heat-up of eight coals (seven Argonne premium coals and an Australian brown coal), an ion-exchange resin, and a lignin were measured every 20 °C from room temperature to 300 °C. Each spectrum was divided into six hydrogen-bonded absorption bands by a curve-resolving method, then the amount of hydroxyls contributing to each hydrogen bond was estimated by Beer's law by using different absorptivity for each band. The strength of each hydrogen bond was estimated using a relation presented by Drago et al. that is known as one of the “linear enthalpy−spectroscopic shift relations”. Us...

FTIR Study of the Thermal Degradation of Poly(vinyl Alcohol)

Abstract: The degradation of poly(vinyl alcohol) was investigated using TG analysis and Fourier transform infrared spectroscopy to determine the effect of atmosphere on the process of degradation. In the spectra, four vibrational modes were identified that characterised the major steps of the degradation process. These were the O-H, C-H, C=O and C=C stretching modes. The mechanism observed for degradation in an inert atmosphere was in accordance with the accepted mechanism of elimination followed by pyrolisation. Evidence of conjugated polyenes, however, was not observed. For the air atmosphere, oxidation in both steps of the degradation process was observed.

Influence of Casting Temperature on the Near-Surface Structure and Wettability of Cast Silk Fibroin Films

Abstract: The near-surface structure and the wettability of silk fibroin films cast from aqueous solutions on hydrophobic polystyrene substrates at various temperatures is investigated by Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) and measurement of contact angle. The FTIR data reveal that the near-surface region of the films is enriched in random coil conformations of the protein at the expense of a reduced fraction of α-helix and β-sheet conformations. The relative random coil/β-sheet content shows a marked dependence on the casting temperature, displaying a minimum at 50 °C. The minimum occurs concurrently with a maximum in the wettability of film surfaces by polar liquids. In the lower wettability region, the film surfaces of this hydrophilic protein are hydrophobic, whereas in the enhanced wettability range they are slightly hydrophilic. The experimental data indicate that during formation of fibron films, α-helix and β-sheet structures are rejected by the interface because ...