Thermal evolution of PEG-based and BRIJ-based hybrid organo-inorganic materials. FT-IR studies

This work presents the application of FT-IR spectroscopy to study the thermal evolution of PEG-based nanocomposites prepared using montmorillonite STx intercalated with polyethylene oxides PEG 1500 and PEG 4000 and polyethylene oxide BRIJ. The effect of different polymer molecular weights and polymer loadings has been evaluated by means of diagnostic mid-IR bands. PEG fragmentation through the cleavage of the CO bond appears to be the main reaction step, leading to the formation of short chain carbonyl adsorbed species (such as acetaldehyde), alcohols (ethanol and methanol) and, to a lesser extent, esters species, characterized by the frequency of the carbonyl stretching band. The detection of carbonyl band evidenced the formation of partial oxidation products as first step of the thermal degradation.Increasing polymer loadings, as well as increasing polymer molecular weight leads to lower temperature of formation of the first oxidation products. No clear indication of the effect of the chemical nature for the intercalated polymers can be obtained. BRIJ thermal decomposition seems to be mainly driven by the PEG-like moiety chemistry.CH stretching bands detected at 450–500 °C for the samples intercalated with PEG samples indicated the formation of residual organic compounds resisting oxidation, possibly char species preserved from further oxidation by the interlayer galleries.     

Near-infrared and mid-infrared investigations of Na-dodecylbenzenesulfate intercalated into hydrocalumite chloride (CaAl-LDH-Cl)

Hydrocalumite (CaAl-LDH-Cl) belongs to layered double hydroxides (LDHs). The intercalation of Na-dodecylbenzenesulfate (SDBS) into CaAl-LDH-Cl has been investigated by X-ray diffraction (XRD), mid-infrared (MIR) spectroscopy and near-infrared (NIR) spectroscopy. The mid-infrared spectra indicated that SDBS could be intercalated into CaAl-LDH-Cl, with the same lattice structure to that of CaAl-LDH-Cl, and the interlayer distance of resultant product was expanded to 2.78 nm as confirmed by XRD. The near-infrared spectra (9200-4000 cm(-1)) showed that a special spectral range from 6200 to 5600 cm(-1) and prominent bands of CaAl-LDH-Cl intercalated with SDBS around 8300 cm(-1). This band was assigned to the second overtone of the first fundamental of C-H stretching vibrations of SDBS, and can be used to determinate the result of CaAl-LDH-Cl modified by anionic surfactants. The bands of water stretching vibrations and -OH groups shifted to higher wavenumbers when CaAl-LDH-Cl was intercalated by SDBS, and their intensity of MIR and NIR spectra became lower in intensity.     

Bonding mechanisms and conformation of poly(ethylene oxide)-based surfactants in interlayer of smectite

A better understanding of the interactions between poly(ethylene oxide) (PEO)-based nonionic surfactants and smectite is important to fully comprehend the transport and the fate of nonionic surfactants in the environment and to design novel organo-clay composites. We studied the bonding between the surfactants and smectite and the molecular conformations of the surfactants in the interlayer of smectite. A reference polymer PEG and three nonionic surfactants—Brij 56, Brij 700, and PE-PEG—were intercalated into a smectite. The polymers and the composites were characterized with X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The XRD and FT-IR results indicate that the bulk surfactants existed as crystalline materials at room temperature, and surfactant molecules had both helical/extended diblock and planar zigzag conformations. The surfactants intercalated smectite and expanded the d(001) spacing of smectite to nearly 1.8 nm. The shapes and positions of the IR bands of interlayer surfactants were similar to those of the melted (amorphous) bulk polymers: the wagging vibrations of the CH₂ merged to a single band at 1,350 cm⁻¹, the twisting bands of CH₂ had 9 cm⁻¹ or more blue shifts. These changes imply that the PEO segments of the surfactants existed with a distorted and extended conformation in the interlayer of smectite, and this extended conformation was an intermediate form of the helical and planar zigzag conformations. The molecular conformation of the interlayer surfactant was not affected by the seven types of exchangeable cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cu²⁺, Ni²⁺, and H⁺) tested. There were 20 cm⁻¹ or more red shifts from the C–O–C stretching bands when the surfactants were adsorbed. The red shifts suggest that surfactants were bonded to smectite mainly through (1) H-bonding between oxygen atoms of the PEO segments and water molecules in hydration shells of the exchangeable cations, and (2) direct coordination or ion–dipole interaction between the oxygen atoms of the PEO segments and the exchangeable cations. With the extended conformation, the oxygen atoms of the PEO segments have maximum exposure to the bonding water molecules and exchangeable cations.     

Raman spectroscopy of urea and urea-intercalated kaolinites at 77 K

The Raman spectra of urea and urea-intercalated kaolinites have been recorded at 77 K using a Renishaw Raman microprobe equipped with liquid nitrogen cooled microscope stage. The NH2 stretching modes of urea were observed as four bands at 3250, 3321, 3355 and 3425 cm(-1) at 77 K. These four bands are attributed to a change in conformation upon cooling to liquid nitrogen temperature. Upon intercalation of urea into both low and high defect kaolinites, only two bands were observed near 3390 and 3410 cm(-1). This is explained by hydrogen bonding between the amine groups of urea and oxygen atoms of the siloxane layer of kaolinite with only one urea conformation. When the intercalated low defect kaolinite was cooled to 77 K, the bands near 3700 cm(-1) attributed to the stretching modes of the inner surface hydroxyls disappeared and a new band was observed at 3615 cm(-1). This is explained by the breaking of hydrogen bonds involving OH groups of the gibbsite-like layer and formation of new bonds to the C=O group of the intercalated urea. Thus it is suggested that at low temperatures two kinds of hydrogen bonds are formed by urea molecules in urea-intercalated kaolinite.     

Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide-water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 A was observed with subtle differences whether the kaolinite was expanded with formamide or formamide-water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm(-1). These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm(-1) Raman band separated into two bands at 3633 and 3625 cm(-1). DRIFT spectra showed the hydroxyl deformation mode at 905 cm(-1). Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm(-1) attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm(-1) and are attributed to the amide 1 and amide 2 vibrations.     

Cd(II) extraction in PEG-based two-phase aqueous systems in the presence of iodide ions. Analysis of PEG-rich solid phases

Cd(II) plus iodide species were extracted into PEG-rich phases in the aqueous PEG(1550)-(NH₄)₂SO₄ system at pH 2.05–7.12. IR spectra show that increasing (NH₄)₂SO₄ solution acidity does not protonate PEG ether oxygen atoms, but decreases water content in the PEG-rich phases. Metallic species’ extraction into the PEG predominantly alters how water molecules bind to polymer chains; the changes in their absorption bands depend on pH. Microscopy shows that “fixation” of the extracted metal in the PEG-rich phase occurs by specific interactions which depend on the species. These also determine changes in the polymer chains’ conformation.     

Infrared study of HDTMA+ intercalated montmorillonite

In this paper, FTIR spectroscopy using attenuated total reflection (ATR) and KBr pressed disk techniques has been used to characterize sorbed water and HDTMA+ in organo-clay. Sorbed water content decreases with the intercalation of HDTMA+. With the decrease of the sorbed water content, the position of the nu2 mode shifts to higher frequency dramatically while the stretching vibration shifts to lower frequency slightly, indicating that H2O is less strongly hydrogen bonded. This might be resulted from the polarization of H2O molecules by the changeable cations and HDTMA+. FTIR spectra show that both antisymmetric and symmetric CH2 stretching absorption bands shift to low frequencies with increase of amine concentration within the galleries of montmorillonite, elucidating the increase of ordered conformation. Furthermore, the present study demonstrates that the antisymmetric CH2 stretching mode is more sensitive to the conformational ordering than the symmetric stretching mode. When KBr pressed disk technique used, two well resolved absorption bands at 730 and 720 cm(-1), and at 1473 and 1463 cm(-1), corresponding to the methylene scissoring and rocking modes, respectively, could be observed in FTIR spectra of organo-clays with relative higher concentration of surfactant. However, the FTIR spectra using ATR technique only display singlets and they are independent of amine concentration and chain conformation. Our present study demonstrates that FTIR spectroscopy using KBr pressed disk technique is more suitable to probe the conformational ordering of surfactant in organo-clays than that suing ATR technique does.     

Molecular configurations and orientations of hydrazine between structural layers of kaolinite

Hydrazine is one of the most commonly used entraining agents to penetrate kaolinite, yet the mechanism of intercalation of kaolinite by hydrazine is still in debate. The objectives of this study are to investigate the possible molecular configurations and orientations of hydrazine in the interlayer of kaolinite and the configuration changes induced by water molecules. Water molecules increased the intercalation rate and caused the expansion of the intercalation complex from 0.96 to 1.03 nm. The kinetic effect was likely the result of breaking the self-associations of hydrazine molecules and releasing more "free" hydrazine molecules for the intercalation. H-bonding caused large red shifts of the inner surface OH stretching bands from 3695 to 3626 cm(-1) in the 0.96-nm kaolinite hydrazine intercalation (KHI) complex and to 3570 and 3463 cm(-1) in the 1.03-nm KHI complex. The NH stretching bands of the hydrazine molecules in the KHI complexes became sharper and blue-shifted more than 20 cm(-1) compared with the free liquids. The symmetric NH vibrations at 3365 and 3310 cm(-1), and the NN vibration at 1092 cm(-1) became infrared inactive in the 0.96-nm KHI complex. The frequency of the SiO bands of the kaolinite in the 1.03-nm KHI complex was slightly lower than in the 0.96-nm KHI complex (5 cm(-1) shift). These IR band changes implied that hydrazine molecules have different configurations in the complexes: hydrazine molecules had an eclipsed form in the interlayer of the 0.96-nm KHI complex. The eclipsed configuration has a dipole moment of 3.31 D, which is higher than the gauche form (1.83-1.90 D). The molecule was oriented with the NN bond parallel or nearly parallel to the (001) surface of the mineral and the four H atoms of each hydrazine molecule reacted with the basal siloxane surface. When a suitable amount of water was present, it promoted the configuration change of the hydrazine molecules from the eclipsed form to the common gauche form. This gauche form was stabilized by transforming to a more polarized NH3NH tautomer structure (5.4 D). To promote an optimal interaction between hydrazine and the mineral surface, the NN bond of the hydrazine was tilted about 30 degrees from the (001) plane and caused the intercalation complex to expand from 0.96 to 1.03 nm. The eclipsed form and the tautomer were stabilized by the asymmetric interlayer environment of kaolinite. The two proposed models and reaction mechanisms match the high dipole moment requirement as found for other entraining agents. Further investigation is needed to confirm the exact configuration of hydrazine molecules and whether or not the tautomer exists.     

Influence of particle size on the in vitro digestibility of protein-coated lipid nanoparticles

The development of new materials for water purification is of universal importance. Among these types of materials are layered double hydroxides (LDHs). Non-ionic materials pose a significant problem as pollutants. The interaction of methyl orange (MO) and acidic scarlet GR (GR) adsorption on hydrocalumite (Ca/Al-LDH-Cl) was studied by X-ray diffraction (XRD), infrared spectroscopy (MIR), scanning electron microscope (SEM), and near-infrared spectroscopy (NIR). The XRD results revealed that the basal spacing of Ca/Al-LDH-MO was expanded to 2.45 nm, and the MO molecules were intercalated with a interpenetrating bilayer model in the gallery of LDH, with 49° tilting angle. Yet, Ca/Al-LDH-GR was kept the same d-value as Ca/Al-LDH-Cl. The NIR spectrum for Ca/Al-LDH-MO showed a prominent band around 5994 cm(-1), assigned to the combination result of the NH stretching vibrations, which was considered as a mark to assess MO(-) ion intercalation into Ca/Al-LDH-Cl interlayers. From SEM images, the particle morphology of Ca/Al-LDH-MO mainly changed to irregular platelets, with a "honey-comb" like structure. Yet, the Ca/Al-LDH-GR maintained regular hexagon platelets, which was similar to that of Ca/Al-LDH-Cl. All results indicated that MO(-) ion was intercalated into Ca/Al-LDH-Cl interlayers, and acidic scarlet GR was only adsorbed upon Ca/Al-LDH-Cl surfaces.     

Vibrational spectroscopy of formamide-intercalated kaolinites

The vibrational spectroscopy of low and high defect kaolinites fully and partially intercalated with formamide have been determined using a combination of X-ray diffraction, DRIFT and Raman spectroscopy. Expansion of the high defect kaolinite to 10.09 A resulted in a decrease in the peak width of the d(001) peak attributed to a decrease in defect structures upon intercalation. Changes in the defect structures of the low defect kaolinite were observed. Additional infrared bands were observed for the formamide intercalated kaolinites at 3629 and 3606 cm(-1). The 3629 cm(-1) band is attributed to the hydroxyl stretching frequency of the inner surface hydroxyl group hydrogen bonded to the carboxyl group of the formamide. The 3606 cm(-1) band is ascribed to water in the interlayer. Concomitant changes are observed in both the hydroxyl deformation modes and in the carboxyl bands.     

Spectral properties of TMPyP intercalated in thin films of layered silicates

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.     

The Modification of Hydroxyl Surfaces of Formamide-Intercalated Kaolinites Synthesized by Controlled Rate Thermal Analysis

Controlled rate thermal analysis (CRTA) technology made possible the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. X-ray diffraction shows that the CRTA-treated formamide-intercalated kaolinites remain expanded after CRTA treatment. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites with both intercalated and adsorbed formamide. An intense band is observed at 3629 cm(-1), attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm(-1) and are attributed to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl stretching band of the inner hydroxyl is readily observed at 3621 cm(-1) in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. The Raman bands of the formamide in the CRTA-treated intercalated kaolinites are readily observed. Copyright 2001 Academic Press.     

Thermo-infrared-spectroscopy analysis of dimethylsulfoxide-kaolinite intercalation complexes

Dimethylsulfoxide (DMSO) kaolinite complexes of low-and high-defect kaolinites were studied by thermo-IR-spectroscopy analysis. Samples were gradually heated up to 170°C, three hours at each temperature. After cooling to room temperature, they were pressed into KBr disks and their spectra were recorded. From the spectra two types of complexes were identified. In the spectrum of type I complex two bands were attributed to asymmetric and symmetric H-O-H stretching vibrations of intercalated water, bridging between DMSO and the clay-O-planes. As a result of H-bonds between intercalated water molecules and the O-planes, Si-O vibrations of the clay framework were perturbed, in the low-defect kaolinite more than in the high-defect. Type II complex was obtained by the thermal escape of the intercalated water. Consequently, the H-O-H bands were absent from the spectrum of type II complex and the Si-O bands were not perturbed. Type I complex was present up to 120°C whereas type II between 130 and 150°C. The presence of intercalated DMSO was proved from the appearance of methyl bands. These bands decreased with temperature due to the thermal evolution of DMSO but disappeared only in spectra of samples heated at 160°C. Intercalated DMSO was H-bonded to the inner-surface hydroxyls and vibrations associated with this group were perturbed. Due to the thermal evolution of DMSO the intensities of the perturbed bands decreased with the temperature. They disappeared at 160°C together with the methyl bands.     

An infrared study of adsorption of para-nitrophenol on mono-, di- and tri-alkyl surfactant intercalated organoclays

Infrared spectroscopy has been used to study the adsorption of para-nitrophenol on mono-, di- and tri-alkyl surfactant intercalated montmorillonite. Organoclays were obtained by the cationic exchange of mono-, di- and tri-alkyl chain surfactants for sodium ions [hexadecyltrimethylammonium bromide (HDTMAB), dimethyldioctadecylammonium bromide (DDOAB), methyltrioctadecylammonium bromide (MTOAB)] in an aqueous solution with Na-montmorillonite. Upon formation of the organoclay, the properties change from strongly hydrophilic to strongly hydrophobic. This change in surface properties is observed by a decrease in intensity of the OH stretching vibrations assigned to water in the cation hydration sphere of the montmorillonite. As the cation is replaced by the surfactant molecules, the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Bands attributed to CH stretching and bending vibrations change for the surfactant intercalated montmorillonite. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

Structure analysis of intercalated layer silicates: combination of molecular simulations and experiment

Na(+)-montmorillonite type Wyoming, cloisite Na(+) from Southern Clay Products, Inc., was intercalated (i) with octadecylammonium cations and subsequently intercalated with octadecylamine molecules, (ii) with dodecylamine molecules, and (iii) with octylamine molecules to determine the applicability of these intercalates for nanocomposite materials on the base of polymer/clay. The structures were determined on the basis of a combination of results from X-ray diffraction and molecular simulations. The calculated values of basal spacings are in good agreement with experimental basal spacings when experimental samples were prepared. The interlayer space of intercalated montmorillonite shows a monolayer or bilayer arrangement of alkyl chains in dependence on the concentration of the intercalation solution. The values of the total sublimation energy, interaction energy, and exfoliation energy were calculated for all investigated samples. Low values of exfoliation energies lead to better exfoliation of intercalated silicate layers and this material appears suitable for use as a precursor for polymer/clay nanocomposites. The values of exfoliation energy for the investigated samples show that montmorillonite intercalated with dodecylamine or octadecylamine molecules is suitable for exfoliation of silicate layers.     

Adsorbed para-nitrophenol on HDTMAB organoclay--a TEM and infrared spectroscopic study

para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0 CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

聚乙二醇／锂化蒙脱土溶液插层纳米复合的研究

通过溶液插层方法制备了聚乙二醇/锂化蒙脱土纳米复合材料。采用XRD、TEM、电子衍射、TGA及DTA对制得的材料进行了分析和表征。结果表明,聚乙二醇插入到锂化蒙脱土层中形成了具有良好离子导电性的纳米复合材料。     

Anisotropic molecular structure in dip-coated films of linear poly(ethylene imine) studied by infrared multiple-angle incidence resolution spectrometry

Molecular structure in dip-coated films of linear poly(ethylene imine) (LPEI) on a germanium (Ge) substrate in dried and hydrated conditions have been analyzed by infrared multiple-angle incidence resolution spectrometry (IR MAIRS). The MAIRS-IP (in-plane) and -OP (out-of-plane) spectra of the dried film exhibited largely different patterns from each other, which indicated that LPEI molecules had an apparent molecular orientation with respect to the substrate surface. Although the film exhibited no peak in X-ray diffraction patterns, the low-crystallinity film has been found to have highly oriented molecular structure. Many key bands indicated that the molecules were involved in the double-stranded helix structure, which is specific to the anhydrate crystal of LPEI, with nearly perpendicular orientation. The Davydov splitting of the NH stretching vibration mode was readily captured by the IR MAIRS spectra, which also supported the helix standing model. When the film was stored in a humid condition, on the other hand, IR MAIRS spectra revealed that the helix was resolved to be straight chains, but the perpendicular orientation was kept unchanged. In addition, the MAIRS spectra also revealed molecular orientation of the water molecules of crystallization. The unique molecular arrangements are understandable by considering that the stabilization energy in the polymer monolayer directly attached on the substrate surface is minimized by the standing-molecule arrangements.     

PEG在微波诱导下对高岭石插层及剥片的研究

利用微波能量，快速制备了高岭石/DMSO插层复合物，并以其为前驱体，在熔融状态，微波诱导聚乙二醇(PEG)置换出高岭石层间的DMSO，微波继续协同PEG作用，可以实现其对高岭石的剥片。同时提出了微波作用机理和微波条件下插层物对高岭石的剥片机理。采用X-射线衍射、FTIR光谱、TG-DTA、TEM等技术对插层复合物进行了表征。     

Thermal behavior analysis of kaolinite–dimethylsulfoxide intercalation complex

The thermal behavior of kaolinite?Cdimethylsulfoxide intercalation complex was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FT-IR) spectroscopic analysis. The samples gradually heated up to different temperatures were studied by XRD and FT-IR. The kaolinite?Cdimethylsulfoxide intercalation complex is stable below 130?°C. With the rise in the temperature, the relative intensity of the 1.124-nm peak gradually decreased and disappeared at 200?°C, however, the intensity of the 0.714?nm peak increased in the XRD patterns. In the infrared spectra, the appearance of methyl bands at 3018, 2934, 1428, and 1318?cm^?1 indicates the presence of intercalated dimethylsulfoxide, the intensities of these bands decreased with the temperature rising and remained until around 175?°C, which agree with the XRD and TG?CDSC data.