Temperature-dependent Fourier Transform Infrared Research Articles

Glass transition temperature of Agar-Reduced Graphene Oxide (RGO) Composites using 2-D contour mapping of temperature dependent FTIR spectra

In the present work, composites of Reduced Graphene Oxide (RGO) and Agar have been synthesized via the solution cast method and their structural, thermal and dielectric properties are studied. UV–Visible, X Ray Diffraction (XRD), Raman Spectroscopy and Fourier Transform Infrared (FTIR) have been employed for analyzing structural properties of the prepared samples. Analysis of different peaks in XRD and Raman Spectra suggests the interaction of RGO layers with Agar at the molecular level. FTIR spectra indicate that interaction of Agar with RGO occurs through hydrogen bonding linkage. Further, the Glass transition temperature (Tg) of prepared samples has been determined using 2D contour mapping from temperature-dependent FTIR spectra as well as from the Differential Scanning Calorimetry (DSC)technique. Values of Tg obtained from both techniques have been found in close agreement with each other. In addition to that, value of Tg of Agar increases from 72 °C to 80 °C as an effect of 2 wt.% RGO loading indicating the improvement in the thermal behavior of Agar. Moreover, the dielectric behavior of as-prepared composites demonstrate that the dielectric constant of these composites has been increased in comparison to pure Agar.

Understanding Thermal Behavior of Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) Hydrogel Using Two-Dimensional Correlation Infrared Spectroscopy.

In this study, one of the thermoresponsive polymers, block copolymer consisting of poly(ethylene glycol) and poly(N-isopropylacylamide), was investigated using Fourier transform infrared (FT-IR) spectroscopy, principal component analysis (PCA), and two-dimensional correlation spectroscopy (2D-COS). The apparent trend of the spectral changes in the temperature-dependent FT-IR spectra of poly(ethylene glycol)-block-poly(N-isopropylacylamide) (PEG-b-PNiPAAm) hydrogel during the heating process looks similar to that during the cooling process. The results of the PCA and 2D-COS, however, clearly indicate an irreversible phase transition mechanism of PEG-b-PNiPAAm hydrogel during the heating and cooling processes. It has been also shown that PEG affects the phase transition mechanism of PEG-b-PNiPAAm hydrogel, especially during the heating process. Consequently, we can successfully determine the phase transition temperature and the mechanism of PEG-b-PNiPAAm hydrogel during the heating and cooling processes using PCA and 2D-COS, respectively.

Study of phase transitions in a bent-core liquid crystal probed by infrared spectroscopy

A new four ring bent-core liquid crystal (4′-n-octylphenylazo)-phenyl-4-yl-3-[N-(4′-n-dodecyloxy-2-hydroxybenzylidene) amino]-2-methyl benzoate has been synthesized and investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and temperature-dependent Fourier transform infrared (TD-FTIR) spectroscopy. DSC and POM were used to detect transition temperatures and identify mesophases. TD-FTIR spectroscopic technique was utilized as a probe to analyze the dynamics of the liquid crystal molecules during the phase transition. The quantum chemical density functional theory (DFT) was used to predict the most stable conformation and the correct vibrational assignment of different modes. Combined theoretical and experimental techniques provided a clear picture of the structural modifications and dynamics of mesophases during the phase transitions.

Determination of glass transition temperature of reduced graphene oxide-poly(vinyl alcohol) composites using temperature dependent Fourier transform infrared spectroscopy

In the present work, structural properties of reduced graphene oxide (RGO) synthesized using modified Hummer's method and its composites with Poly(vinyl alcohol) (PVA) fabricated using solution-cast method have been studied. The structural properties of prepared samples have been systematically studied through UV–Visible absorption, Raman, Fourier Transform Infrared (FTIR) and Differential Scanning Calorimeter (DSC) spectroscopy. Infrared spectroscopy indicates the grafting of PVA chains with graphene layer through the formation of H-bonding linkage in the composites. Temperature-dependent FTIR spectra of PVA-RGO composite films were recorded to obtain the glass transition temperature (Tg) and to study its molecular origin. From these spectra the values of Tg were obtained using two-dimensional (2D) mapping of the first derivative of the absorbance intensity with respect to temperature (dA/dT), over the space of wavenumber and temperature. The value of Tg obtained for pure PVA increases from 78 °C to 92 °C after loading 0.5 wt.% of RGO in PVA and can be attributed to the strong H–bonding interaction between polymer chains and grafted solid surface of RGO. These results are in good agreement with those obtained from DSC analysis. This clearly indicates that the thermal behavior of PVA gets modified with loading of RGO.

Comparative study of cotton, ramie and wool fiber bundles’ thermal and dynamic mechanical thermal properties

Wool, cotton and ramie thermal properties are qualitatively studied by temperature-dependent Fourier transform infrared (TD-FTIR) spectroscopy, and quantitatively investigated by thermogravimetry coupled with a differential thermal analyzer (TG-DSC). TD-FTIR results indicate that although cotton, ramie and wool exhibit significant water loss, they have no detected degradation within the temperature range from 25℃ to 210℃. These data are confirmed by TG-DSC analysis. Dynamic mechanical thermal analysis provides comparative study of cotton, ramie and wool bundles’ dynamic mechanical thermal properties. The four-fiber-bundle has a much lower storage modulus due to its larger fiber contact surface and twisting deformation; heating reduces the storage modulus significantly for cotton and ramie instead of wool fiber bundles in the temperature range from 25℃ to 100℃. Key E′-T and tan δ-T curve information reveals that ramie fiber bundles have the strongest temperature sensitivity, while wool fiber bundles express the weakest temperature sensitivity.

New insight into amyloid fibril formation of hen egg white lysozyme using a two-step temperature-dependent FTIR approach.

Hen egg white lysozyme (HEWL) is widely used in the mechanistic study of amyloid fibril formation. Yet, the fibrillation mechanism of HEWL is not well understood. In particular, in situ structural evidence for the on-pathway oligomeric intermediate has never been captured. Such evidence is crucial for confirming nucleated conformational conversion mechanism. Herein, we attempt to use a two-step temperature-dependent Fourier transform infrared (FTIR) approach to capture the in situ evidence for the on-pathway oligomeric intermediate and the oligomer-to-fibril transition during HEWL fibrillation. Key features of this approach include using lower temperature to generate the on-pathway oligomeric intermediate, using elevated temperature to eliminate the interference from the off-pathway oligomer and to facilitate the oligomer-to-fibril transition, and using FTIR difference spectroscopy and atomic force microscopy to tackle structure and morphology. Using such an approach, we reveal that the on-pathway oligomeric intermediate is in parallel β-sheet configuration featuring a frequency at 1622 cm(-1) and the oligomer-to-fibril transition is accompanied by a spectral transition from 1622 to 1618 cm(-1). We also discover the beneficial role of the off-pathway oligomer in the capturing of the transient on-pathway oligomeric intermediate by serving as a monomer-releasing reservoir. This approach should also be useful in other amyloidogenic systems.

The role of Nx–Si–Oy bonding configuration in acquiring strong blue to red photoluminescence from amorphous SiNxOy film

We report the acquisition of strong blue to red photoluminescence (PL) from a-SiNxOy thin film that was prepared by plasma enhanced chemical vapor deposition at room temperature. By increasing the flow rate ratio (R) of silane (SiH4) to ammonia (NH3), the luminescent peak position can be tunable in the visible range from 440 to 590 nm, and shown to be independent of temperature as revealed by temperature-dependent PL investigation. The Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) were employed to clarify the relationship between the bonding configuration and PL characteristics. Based on the existence of N–Si–O bond arrangement evidenced in FTIR spectra, the deconvolution of the Si 2p peak was carried out to yield five component peaks corresponding to Si–N4, N3–Si–O, N2–Si–O2, N–Si–O3, and Si–O4. The increase of PL intensity is suggested to be closely related to increased concentration of Nx–Si–Oy bonds. All the results obtained from temperature-dependent PL spectra, FTIR spectra, and XPS spectra disclosed that the light emission from a-SiNxOy film can be originated from recombination via luminescent centers associated with Nx–Si–Oy bonding configuration, and the redshift of PL peak with the increase of R may arise from integral effect of Nx–Si–Oy bonding configuration transformation and valence band maximum upward shift.

Temperature-dependent framework–template interaction of |Na6(H2O)8|[ZnPO4]6 sodalite

The partial dehydration followed by the decomposition of sodium-zincophosphate-hydrosodalite caused by the total water loss was examined by temperature-dependent X-ray powder diffraction, Fourier transform infrared (FTIR) and Raman spectroscopy as well as thermogravimetry combined with difference thermoanalysis. The dehydration causing the decomposition of this sodalite could be described in a two step-process. Initially two water molecules per unit-cell were lost, changing the interaction between the zincophosphate framework and the remaining water molecules as well as sodium cations as non-framework constituents. In this stage a 3+3 coordination of water molecules and sodium cations in the sodalite cage is observed. Using the autocorrelation function (AC) for the evaluation of the temperature-dependent FTIR spectra of sodalites is reported here for the first time. Calculating the changes in the AC broadness, structural features could well be analyzed due to its correlation with respective structural parameters. Temperature dependent Raman data was used to give a band assignment of bands at Raman shifts below 300 cm{sup −1}. - Graphical abstract: The thermal decomposition of |Na{sub 6}(H{sub 2}O){sub 8}|[ZnPO{sub 4}]{sub 6} sodalite is a two-step process with an initial loss of two water molecules at 400 K, intermediately stabilizing the highly stressed framework. Further heating leads to more » a subsequent loss of the remaining six water molecules and a breakup of the sodalite framework. A beryllonite-type NaZnPO{sub 4} is the final product of this process. Display Omitted - Highlights: • The decomposition of |Na{sub 6}(H{sub 2}O){sub 8}|[ZnPO{sub 4}]{sub 6} sodalite is a two-step process. • Initial loss of two water molecule at 400 K stabilizes the sodalite (step 1). • Further heating leads to complete loss of water and structural breakdown. • Autocorrelation of temperature dependent FTIR-spectra gives structural information. « less

Parallel β-Sheet Fibril and Antiparallel β-Sheet Oligomer: New Insights into Amyloid Formation of Hen Egg White Lysozyme under Heat and Acidic Condition from FTIR Spectroscopy

Hen egg white lysozyme (HEWL) is widely used as a model protein for amyloid research. In this study, we aim to use Fourier transform infrared (FTIR) spectroscopy to gain new structural insights into amyloid formation of HEWL under heat and acidic condition. We reveal that the fibril-forming solution of HEWL has the capability to form fibril and oligomer with distinct β-sheet configurations under different temperatures. Amyloid fibril with parallel β-sheet configuration is formed at elevated temperature, while oligomer with antiparallel β-sheet configuration is formed at room temperature. The interplay between fibrillation and oligomerization suggests that the two β-sheet aggregates consume the same amyloidogenic materials such as peptide fragments and nicked HEWL due to lysozyme hydrolysis under heat and acidic condition. Temperature-dependent FTIR reveals that the oligomer is unstable at elevated temperature, demonstrating its off-pathway nature. The temperature-dependent formation of parallel and antiparallel β-sheet configurations discovered in lysozyme system is compared with that of amyloid-β and α-synuclein systems and the implication is discussed.

Synthesis, crystal structure and temperature-dependent behavior of gallogermanate tetrahydroborate sodalite |Na8(BH4)2|[GaGeO4

Tetrahydroborate enclathrated gallogermanate sodalite was successfully synthesized under mild hydrothermal conditions and characterized by X-ray powder diffraction and Fourier transform infrared (FTIR) spectroscopy. The crystal structure was refined in space group P4¯3n using the Rietveld method: a=912.581(1)pm, V=760.0(1)·10−6pm3, RB=0.019. Within the sodalite cage formed by corner-sharing oxygen coordinated gallium and germanium tetrahedra, the hydrogen atoms of the enclathrated BH4− anions were refined on 8e (x, x, x) crystallographic position. The boron–hydrogen distances were restrained to 124.7pm as calculated from the respective bond valence sums. High temperature behavior was investigated using temperature-dependent X-ray diffraction, FTIR and Raman spectroscopy and TG-DTA methods. A two-step sodalite decomposition reaction to the beryllonite analogous phase NaGaGeO4 was observed. The temperature-dependent development of the sodalite structural parameters evaluated by Rietveld analysis of the XRD data indicate a beginning transformation of the enclathrated NaBH4 at about 528K followed by a decomposition of the sodalite framework starting at about 648K. These findings are confirmed by the results obtained from temperature-dependent Raman and FTIR data evaluation.

Molecular motions contributions to optical nonlinearity of N-benzyl-2-methyl-4-nitroaniline studied by temperature-dependent FT-IR, 1H NMR spectroscopy and DFT calculations

The fourier transform infrared (FT-IR) spectra of polycrystalline orthorhombic N-benzyl-2-methyl-4-nitroaniline (BNA) were recorded in the 380–4000cm−1 region within the 11–297K temperature range while the 1H NMR spin–lattice relaxation time and the second moment of 1H NMR resonance line were measured in the 145–373K and 80–400K temperature range, respectively. Above 80K the methyl group rotation is found to be dominant among other motions and leading to a significant reduction of the proton second moment which agrees with proposed models for the rigid structure and for the internal rotations in the BNA crystal such as methyl group C3 rotation, phenyl ring rotation and trans-gauche motion of methylene group. Activation energies for the nitro and methyl group rotations were experimentally estimated by FT-IR and 1H NMR, appropriately. For comparison the potential barriers for these two group motions in BNA molecule were calculated by DFT quantum chemical methods. The role of molecular motions in the BNA crystal in the large temperature range is discussed from the point of view of its nonlinear optical properties.

Hierarchical self-assembly structures of POSS-containing polypeptide block copolymers synthesized using a combination of ATRP, ROP and click chemistry

In this study, we used a combination of atom transfer radical polymerization, ring opening polymerization, and click chemistry to synthesize new organic/inorganic macromolecular self-assembling building blocks of polystyrene-b-poly(γ-propargyl-L-glutamate-g-polyhedral oligomeric silsesquioxane) [PS-b-(PPLG-g-POSS)]. The incorporation of the PS and POSS units enhanced the α-helical conformation in the solid state, as determined using Fourier transform infrared (FTIR) spectroscopy and wide-angle X-ray diffraction (WAXD). Hierarchical self-assembly of the PS-b-(PPLG-g-POSS) diblock copolymers, which we characterized using WAXD, small-angle X-ray scattering, and transmission electron microscopy, led to the formation of cylindrical structures as a result of microphase separation of the diblock copolymer; the hexagonal cylinder packing nanostructure featured α-helical conformations of polypeptide segments, which were oriented perpendicular to the direction of the cylinder column from diblock copolymers; aggregation of the POSS moieties induced the packing into hexagonal lattice structures. The attachment of POSS units onto the side chains of PPLG stabilized the α-helical secondary structures at elevated temperature, relative to those of pure PPLG and PS-b-PPLG, as determined through temperature-dependent FTIR spectroscopic analyses.

Thermotropic Organization of Hydrogen-Bond-Bridged Bolaform Amphiphiles

A series of quaternary ammonium amphiphiles (A-n) bearing carboxylic acid groups were designed and synthesized. The branched bolaform structures can be constructed by dimerizations of carboxylic acid groups through intermolecular hydrogen bonding, as demonstrated by the Fourier transform infrared (FT-IR) spectra and the temperature-dependent FT-IR spectra. The thermotropic organizations of branched bolaform ammonium dimer complexes were characterized by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. We investigated the influence of the spacer between the cationic group and the benzene ring on the thermotropic organization. A-6 with short lateral alkyl chains formed a simple layered structure at room temperature and exhibited smectic A mesophase above 145 °C, whereas A-8 with intermediate lateral chain length organized into smectic A phase over a wide temperature range. A further increase of the length (n = 10, 12) of the lateral chains resulted in the formation of lamellar structure with in-plane layered periodicity, which is rare in the organization of ionic compounds. A packing model of the quasi-2D lamellar was proposed on the basis of the experimental data of X-ray diffraction results. Notably, the quasi-2D lamellar structure could evolve into a simple layer with the increase of temperature. The present results showed a direct relationship in which the branched architecture can be applied to tune the self-assembly behavior of ionic amphiphiles and is allowed to construct new layered superstructure.

Conformational and microstructural characteristics of poly(L-lactide) during glass transition and physical aging

The glass transition and physical aging processes of poly(L-lactide) (PLLA) were studied by variable-temperature Fourier transform infrared (FTIR) spectroscopy and (13)C solid-state NMR spectroscopy. The glass transition temperature (T(g)) of PLLA can be well determined from the temperature-dependent FTIR intensity. Nearby T(g), a distinct change in the slope of spectral intensity versus temperature plot is detected. FTIR results suggest that the energy-favorable gauche-trans (gt) conformers rearrange into the less energy-favorable gauche-gauche (gg) counterparts with heating over the glass transition region, which becomes more distinct at temperature above T(g). Besides, the 1267 cm(-1) band, which shows different trends of variation from the other bands upon heating, was assigned to be more sensitive to the nu(as)(C-O-C)+delta(CH) vibration mode of the less energy-favorable gg conformers in PLLA. By comparing the FTIR spectra of the aged and deaged PLLA, it was demonstrated that the rearrangement from the high- to low-energy conformers, i.e., gg to gt, occurs with physical aging. (13)C spin-lattice relaxation measurements indicate that the relaxation rate distribution broadens with aging, which agrees with the previous suggestion that the locally ordered domains are formed during physical aging. Because of the larger variation in the conformational state and microstructure, the FTIR intensities vary much more abruptly for the aged sample with heating to nearby T(g).

Rapid discrimination of extracts of Chinese propolis and poplar buds by FT-IR and 2D IR correlation spectroscopy

The extract of Chinese propolis (ECP) has recently been adulterated with that of poplar buds (EPB), because most of ECP is derived from the poplar plant, and ECP and EPB have almost identical chemical compositions. It is very difficult to differentiate them by using the chromatographic methods such as high performance liquid chromatography (HPLC) and gas chromatography (GC). Therefore, how to effectively discriminate these two mixtures is a problem to be solved urgently. In this paper, a rapid method for discriminating ECP and EPB was established by the Fourier transform infrared (FT-IR) spectra combined with the two-dimensional infrared correlation (2D IR) analysis. Forty-three ECP and five EPB samples collected from different areas of China were analyzed by the FT-IR spectroscopy. All the ECP and EPB samples tested show similar IR spectral profiles. The significant differences between ECP and EPB appear in the region of 3000–2800 cm −1 of the spectra. Based on such differences, the two species were successfully classified with the soft independent modeling of class analogy (SIMCA) pattern recognition technique. Furthermore, these differences were well validated by a series of temperature-dependent dynamic FT-IR spectra and the corresponding 2D IR plots. The results indicate that the differences in these two natural products are caused by the amounts of long-chain alkyl compounds (including long-chain alkanes, long-chain alkyl esters and long chain alkyl alcohols) in them, rather than the flavonoid compounds, generally recognized as the bioactive substances of propolis. There are much more long-chain alkyl compounds in ECP than those in EPB, and the carbon atoms of the compounds in ECP remain in an order Z-shaped array, but those in EPB are disorder. It suggests that FT-IR and 2D IR spectroscopy can provide a valuable method for the rapid differentiation of similar natural products, ECP and EPB. The IR spectra could directly reflect the integrated chemical compositions of complicated mixtures, and it may be available for use in further chromatographic analysis.

Temperature-dependent FTIR spectroscopic and thermoanalytic studies of hydrogen bonding of hydroxyl (phenolic group) terminated hyperbranched aromatic polyesters

The formation and modification of inter- and intramolecular hydrogen bonds of hydroxyl (phenolic group) terminated hyperbranched aromatic polyesters (HBP-OH) have been studied by temperature-dependent Fourier transform infrared (FTIR) spectroscopy. Three ‘heating–annealing–cooling’ (HAC) cycles starting from room temperature to 235 °C were measured. The IR spectroscopic results indicate different types of hydrogen bond association. The weakening and breaking of hydrogen bonds with increasing temperature was observed. Additionally, a curve fitting procedure of the hydroxyl and carbonyl vibration regions has been done to gather additional information of the hydrogen bond association. On the basis of the band shifts and the changes of the normalised integral band intensity (NIBI) and halfwidth of a band (HWB), the formation of a network of hydrogen bonds was proposed. Four different interactions regarding hydroxyl (phenolic) groups association were detected. Several types of associated carbonyl groups existing within HBP-OH were revealed. The spectra and curve fitting results indicate the relative stability of formed bond structures with participation of the ester groups of the HBP rigid segments in the studied temperature region. Differential scanning calorimetry (DSC) was applied to reveal changes in thermal behaviour after the first, the second and the third HAC cycle. As expected, the aromatic ester backbone structure strongly influences the glass transition. Therefore, the performed measurements did not show any changes in glass transition related to the rearrangements in the hydrogen bonded network.

Molecular Aggregation State and Molecular Motion of Organosilane Monolayers Prepared at the Air/Water Interface

Relationships between the molecular aggregation state and the molecular motion of organosilane monolayers with various chain lengths prepared by the Langmuir−Blodgett (LB) method were investigated by lateral force microscopic, Fourier transform-infrared (FT-IR) spectroscopic, and electron diffraction (ED) measurements. The lateral force of the organosilane monolayers increased with increasing their chain length. This is mainly because the intermolecular cohesive energy is proportional to the number of carbons in a chain. The lateral force of the alkylsilane monolayer was compared with that of the fluoroalkylsilane monolayer for the corresponding alkyl chain length. Consequently, the fluoroalkylsilane monolayer showed higher lateral force than the alkylsilane one. Temperature-dependent ED and FT-IR measurements revealed that the molecular aggregation state of the n-octadecyltrichlorosilane (OTS) monolayer changed from the rectangular lattice to the amorphous state via the hexagonal lattice with increasing ...

Well-Ordered Structure and Phase Transition Behaviors of a Reversed Duckweed Polymeric Langmuir−Blodgett Film Studied by Fourier Transform Infrared Spectroscopy and Small-Angle X-ray Diffraction

A Reversed Duckweed polymeric Langmuir−Blodgett (LB) film was characterized by Fourier transform infrared (FTIR) spectroscopy. It has a well-ordered structure which is similar to that of the monomeroctadecylacrylamideLB film, which provides proof that the flexible hydrophilic network does not interfere the side-chain alignment. The phase transition behavior was studied by using temperature dependent FTIR and small-angle X-ray diffraction. The LB film shows a unique thermal transition behavior, which undergoes a three-phase transition processes: from a highly ordered structure transition into a melted disordered state through two Langmuir−Blodgett “liquid crystal” states.

Vibrational spectra, molecular structure and rotational isomerism in “staircase” carbonyl complexes of transition metals

Abstract Fourier transform infrared (FT-IR) spectra have been studied of “staircase” cyclopentadienyl complexes containing two or three metal carbonyl fragments bound by the metal-carbon bond Cp(CO) 2 Fe-CpmMn(CO) 3 ( I ), Cp(CO) 2 Fe-CpmFe(CO) 2 CH 2 Ph ( II ), Cp(CO) 2 Fe-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( III ), Cp(CO) 2 Mo-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( IV ), Cp(CO) 3 W-Cpm(CO) 2 Fe-CpmMn(CO) 3 ( V ), Cp(CO) 2 Fe-Cpm(CO) 2 Fe-BmCr(CO) 3 ( VI ), Cr(CO) 3 Bm-CpmFe(CO) 2 CH 2 Ph ( VII ), where Cp = η 5 : η 5 -C 5 H 4 , Bm = η 1 : η 6 -C 6 H 5 , as well as model mononuclear complexes Cp(CO) 2 FeCH 2 Ph (VIII), CpMn(CO) 3 ( IX ), and ( η 6 -C 6 H 6 )Cr(CO) 3 ( X ). The spectra were interpreted on the basis of the local symmetry of each metal carbonyl center. The v CC positions are determined by the mutual electronic effects of each center. CpmM(CO) n groups are strong electron acceptors and cause an increase in the v CO of adjacent M(CO) n groups. Cp(CO) n M groups, being electron donors, lead to a decrease in the frequencies of neighbouring groups. Temperature dependent FT-IR spectra in pentane solutions and solid matrices were measured. Rotational isomers, formed due to rotation about the metal-carbon bond, were found in solutions and solid matrices. A molecular mechanics calculation for I proved the possibility of such rotation.