Studies of wall painting fragments from Kaiping Diaolou by SEM/EDX, micro Raman and FT-IR spectroscopy

The multi-technique analytical approach has proved to be a very effective tool for the analysis of artwork, as demonstrated by various studies. In this work, four micro-analysis methods were used to analyze the wall painting fragments in Kaiping Diaolou, a world cultural heritage enlisted in 2007. Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray micro-analysis (EDX), combined with micro Raman and Fourier transform infrared (FT-IR) spectroscopy, provided a vast amount of information concerning the raw materials present in the pigments, organic binder, plasters and mortars of the wall painting. Four types of pigments (goethite, lazurite, chromium green and calcite) were identified on the surface layer of the wall paintings. The substrate under the pigment layer was found to be composed of cubic-like calcite (CaCO₃), micro-rod bundle-shaped syngenite (K₂Ca(SO₄)₂·H₂O), gypsum (CaSO₄·2H₂O) and silica (SiO₂). The organic binder can be attributed to animal glue (such as egg) and drying oil by micro FT-IR spectroscopy. These analysis results can provide important information for the conservation and restoration of the Kaiping Diaolou.     

Diffusion of poly(ethylene glycol) and ectoine in NIPAAm hydrogels with confocal Raman spectroscopy

The diffusion behavior of poly(ethylene glycol) (PEG) in N-isopropylacrylamide (NIPAAm) hydrogels was investigated using confocal Raman spectroscopy with regard to temperature (25°C, 30°C and 35°C), PEG concentration (10 and 40?wt.%), PEG molecular weight (2,000 and 12,000?g/mol) and addition of the compatible solute ectoine (0.1 and 2?wt.%). Swelling and shrinking of the gels was observed by means of confocal Raman spectroscopy. The swelling behavior of NIPAAm gels in aqueous solutions of PEG and ectoine was found to resemble the swelling behavior in pure water with regard to temperature, i.e., the gel shrinks with increasing temperature. However, the presence and concentration of PEG and ectoine influence the swelling behavior by lowering the volume phase-transition temperature of the gel and facilitating shrinking. In some cases, a re-swelling of the gel was observed after the initial shrinking at the onset of PEG diffusion, which can be explained by PEG changing the chemical potential in the gel phase as it diffuses into the sample allowing the water to re-enter. The expulsion of water from the gel during shrinking and the so-caused increase of PNIPAAm and PEG concentrations in some cases led to the PEG diffusion seemingly being faster in more shrunken gels despite of their higher diffusion resistance.     

Use of Raman spectroscopy as an in situ tool to obtain kinetic data for organic transformations

Raman spectroscopy has been used as an in situ tool to obtain kinetic data for an organic transformation. The model reaction studied was the synthesis of 3-acetylcoumarin from the condensation between salicylaldehyde and ethyl acetoacetate with piperidine as a catalyst. The study shows that precise kinetic data can be obtained quickly and reproducibly, allowing for the facile determination of both overall reaction order and reaction order with respect to each component of the reaction. Additionally, Arrhenius parameters such as activation energy for a reaction can be readily obtained. In conjunction with computational modeling, this data-rich analysis technique also allows for in-depth probing of mechanistic aspects of reactions. Microwave heating proves to be an ideal tool for aiding in kinetic studies. It offers reproducible noncontact heating as well as precise temperature monitoring and data recording.     

Differential scanning calorimetry (DSC) and Raman spectroscopy study of poly(dimethylsiloxane)

Poly(dimethylsiloxane) was studied by laser Raman spectroscopy and differential scanning calorimetry. The Si O Si skeletal mode at 489 cm⁻¹ and the C Si C deformation bands at 188 cm⁻¹ and 158 cm⁻¹ were studied as functions of temperature from ambient to −130°C, and effects of temperature interpreted in accordance with results from thermal analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2805–2810, 1998     

Characterization of pigments and ligands in a wall painting fragment from Liternum archaeological park (Italy)

Spectroscopic and MS techniques were used to characterize the pigments and the composition of polar and nonpolar binders of a stray wall painting fragment from Liternum (Italy) archaeological excavation. X‐ray fluorescence and diffraction analysis of the decorations indicated mainly the presence of calcite, quartz, hematite, cinnabar, and cuprorivaite. Infrared spectroscopy, GC coupled to flame‐ionization detector, and MS analysis of the polar and nonpolar components extracted from paint layers from three different color regions revealed the presence of free amino acids, sugars, and fatty acids. Interestingly, LC‐MS shotgun analysis of the red painting region showed the presence of αS1‐casein of buffalo origin. Compared to our previous results from Pompeii's wall paintings, even though the Liternum painting mixture contained also binders of animal origin, the data strongly suggest that in both cases a tempera painting technique was utilized.     

The use of laser Raman spectroscopy to study the degradation of poly(vinyl chloride)

The results of natural weathering tests carried out on plasticised poly(vinyl chloride) in three different locations representing cool/wet, hot/wet and hot/dry climates are detailed. The value of laser-Raman spectroscopy for determining dehydrochlorination levels of naturally weathered samples is demonstrated. The results indicate that plasticisers can play a significant role in this dehydrochlorination process. Results of studies on the effects of thermal stabilisers and amines, particularly those used as catalysts for polyurethane foam formation, on the stability on poly(vinyl chloride) are also reported.     

A Raman spectroscopy study of hydroxo and carbonato species of the uranyl (VI) ion

The Raman spectra of a number of uranyl species in carbonate and alkaline solutions have been obtained as well as those of solids obtained from carbonate media. The frequency of the UO₂−ν₁ symmetric stretching vibration of these species can be used to complement evidence derived by other means in their identification. Thus, the existence of uranyl hemicarbonate, (UO₂)₂CO₃(OH)₃⁻, has been demonstrated as well as that of anionic hydroxo species, such as UO₂(OH)₄²⁻. The conversion of UO₂(CO)₃²⁻ into UO₂(CO₃)₃⁴⁻ by addition of HCO₃⁻ was followed by Raman spectroscopy and ¹³C NMR. Solid solutions with compositions within that of UO₂CO₃ and sodium uranate have been detected. A correlation was observed between the ν₁ frequency and the number and nature of the ligands surrounding the uranyl ion.     

Development of new approach based on Raman spectroscopy to study the dispersion of expanded graphite in poly(lactide)

A new approach has been developed to study the dispersion/delamination of expanded graphite (EG) in poly(lactide) (PLA) by using Raman spectroscopy. This technique is more sensitive and therefore fully complementary to more standard dispersion characterization techniques like SEM, TEM and X-ray diffraction. The incorporation of EG into PLA was carried out by a twin-screw micro-extruder. The effects of the dispersion and delamination of EG on the thermal and thermo-mechanical properties of polylactide-EG nanocomposites were investigated. In contrast to the standard techniques, Raman spectroscopy was able to show a partial exfoliation, which could therefore explain the slight improvement of the PLA-EG thermal and thermo-mechanical properties.     

Application of band-target entropy minimization (BTEM) and residual spectral analysis to in situ reflection-absorption infrared spectroscopy (RAIRS) data from surface chemistry studies

The band-target entropy minimization (BTEM) curve resolution technique has been used to analyze in situ reflection-absorption infrared spectroscopy (RAIRS) data of CO chemisorption on Ni(1 1 1) single crystal surfaces. The bilinearity assumption for pRAIRS data, that is, negative logarithm to the base 10 of raw reflectance RAIRS data, was found to be sufficiently valid for the test data. A total of 11 real pure component pRAIRS spectra were elucidated via BTEM in tandem with an iterative residual spectral data analysis. Furthermore, 2 abstract pure component right singular vectors were found to account for all the pRAIRS non-linearities, baseline drifts and other spectral noise. In total, 100.2% of the pRAIRS signals were accounted for by these 13 spectral components. The 11 real pure component pRAIRS spectra and their corresponding relative concentration kinetic sequences correlate with 6 well-known adsorbed CO domain structures. Moreover, amongst the BTEM resolved spectra were five new bands that were not previously observed using conventional visual identification methods adopted by surface chemists. These new bands engendered new understanding to the mechanism of CO chemisorption on Ni(1 1 1). The combination of BTEM with residual spectral analysis was thus demonstrated to be efficacious for curve resolution of in situ RAIRS data obtained from surface chemistry studies.     

Thermophysical study of lead(II) n-alkanoates by DSC, optical microscopy, FTIR and Raman spectroscopy

Thirteen members of the lead(II) n-alkanoate series (from the n-hexanoate to the n-octadecanoate) have been synthesized, purified, and studied by differential scanning calorimetry, polarizing light microscopy, and FTIR and Raman spectroscopy. A solid-solid transition was found for all members of the series. A mesomorphic state, implying a fusion and a clearing point, was identified as smectic C, and was present only in the lower members of the series below the n-tridecanoate. The higher members form the isotropic liquid through a regular fusion. Temperatures and enthalpies for the phase transitions have been measured and the corresponding entropy changes calculated. Heat capacity measurements between 280 K and 400 K were also carried out. A study of these magnitudes versus number of carbons was made. The solid phase previous to the liquid crystal in the lower members and to the isotropic liquid in the higher members could be identified as a 'condis' crystal (conformationally disordered phase) by an FTIR versus temperature study.     

Pressure-dependent Raman spectroscopy of metal-oxo multiple bonds in rhenium(V) and osmium(VI) complexes

The pressure dependence of stretching vibrations involving metal-oxo multiple bonds is reported and discussed. Metal–ligand vibrational frequencies involving double and triple bonds increase with pressure according to the nature of the metal center and ancillary ligands. Pressure-dependent luminescence spectra, at room temperature, of a trans-dioxo rhenium(V) complex exhibit resolved vibronic structure with a progression in a high frequency metal-oxo stretching mode that shows a change of the intensity distribution with pressure. Raman and luminescence spectra are used to rationalize the unusual decrease of the metal-oxo stretching frequency observed for two complexes at pressures over 30 kbar.     

Resonance Raman spectroscopy and density functional theory calculation study of photodecay dynamics of tetra(4-carboxyphenyl) porphyrin

The 397.9 nm, 416.0 nm and 435.7 nm resonance Raman spectra were acquired for meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP) in tetrahydrofuran solution, and the Raman effect of relaxation dynamics was analyzed according to Herzberg-Teller (vibronic coupling) contributions. Density functional calculations were done to help the elucidation of the Soret (B(x) and B(y)-band) electronic transitions and the corresponding photo relaxation dynamics of TCPP. The spectra indicate that the Franck-Condon region photo relaxation dynamics upon S(0) → S(4) electronic transition are predominantly along the totally symmetric C(m)-ph stretch and Porphin ring breath stretch, and simultaneously along the asymmetric ν(C(m)-Phenyl) + δ(N-H) and ν(C(α)-C(m)-C(α))(as) + def (pyr) vibrational relaxation processes. The excited state structural dynamics of TCPP determined from the resonance Raman spectra show that the internal conversion between the B(y) and B(x) electronic states occurs in tens of femtoseconds, and the electronic relaxation dynamics were firstly interpreted taking into account the time-dependent wave packet theory and Herzberg-Teller (vibronic coupling) contributions.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

High pressure study of Ru3(CO)12 by X-ray diffraction, Raman, and infrared spectroscopy

The single-crystal X-ray structure of Ru(3)(CO)(12) is reported at 8 pressures ranging from 1 atm (0.0 GPa) to 8.14(5) GPa. Although intramolecular bonding parameters remain relatively constant, intramolecular and intermolecular nonbonding contact distances decrease by an average of 4% and 15%, respectively. At 8.14 GPa, O...O, C...O, and C...C intermolecular distances as short as 2.54(4), 2.64(6), and 3.07(4) A, respectively, are observed, and the unit cell compresses to 75% of the ambient pressure volume. Raman and infrared spectroscopic measurements show that carbonyl stretching frequencies shift to higher wavenumber values by as much as 80 cm(-)(1), even though Ru-C and C-O distances stay roughly constant throughout the entire pressure range studied. Compression of the sample to above 18 GPa with laser radiation results in an irreversible transformation due to either decomposition or a total collapse of D(3)(h) molecular geometry accompanied by color darkening.     

Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study

The adsorbate species present during partial oxidation of methanol on a Cu(110) surface have been investigated in the 10(-5) mbar range with in situ x-ray photoelectron spectroscopy and rate measurements. Two reaction intermediates were identified, methoxy with a C 1s binding energy (BE) of 285.4 eV and formate with a C 1s BE of 287.7 eV. The c(2x2) overlayer formed under reaction conditions is assigned to formate. Two states of adsorbed oxygen were found characterized by O 1s BE's of 529.6 and 528.9 eV, respectively. On the inactive surface present at low T around 300-350 K formate dominates while methoxy is almost absent. Ignition of the reaction correlates with a decreasing formate coverage. A large hysteresis of approximately 200 K occurs in T-cycling experiments whose correlation with adsorbate species was studied with varying oxygen and methanol partial pressures. The two branches of the hysteresis differ mainly in the amount of adsorbed oxygen, the methoxy species, and a carbonaceous species. Methoxy covers only a minor part of the catalytic surface reaching at most 20%. Above 650 K the surface is largely adsorbate-free.     

Combined use of FORS,XRF and Raman spectroscopy in the study of mural paintings in the Aosta Valley (Italy)

Mural paintings which decorate the external façade and the internal apsidal wall of a chapel dedicated to St. Maxime and located at Challand St. Victor in the Aosta Valley (Italy) have been analysed with a combined approach involving high-resolution fibre-optic reflectance spectroscopy (FORS), X-ray fluorescence (XRF) spectrometry and Raman spectroscopy. The paintings are attributed to Giacomino from Ivrea, a painter active around the mid-fifteenth century. In order to characterise the palette used by the painter and to yield information useful to restorers, the cited techniques were used either in situ with portable instruments and in laboratory, working on micro samples withdrawn from paintings. The global analytical approach, though not entirely non-invasive, can indeed be considered non-destructive as multiple analyses, including SEM-EDX, could be carried out on the micro samples, exploiting the features of each technique. On the basis of the information obtained, the palette was found to be composed of typical fresco pigments such as calcite, azurite, malachite, vermilion, red and yellow ochres. A particular situation was noted for black pigments since the presence of graphite, rather than wood or lamp carbon, was found, possibly related to the presence of graphite deposits in the Aosta Valley. Furthermore, the presence of smalt superimposed to azurite in areas showing evidence of repainting was detected, suggesting that paintings were subjected to retouching at a relatively early stage after the original execution. Finally, the presence of tin foils, used to decorate haloes of Evangelists, was ascertained.     

The application of Fourier transform Raman spectroscopy to the analysis of poly(anhydride) homo- and co-polymers

Fourier transform Raman spectroscopy was used to characterise a homologous series of aliphatic poly(anhydrides), poly[bis(p-carboxyphenoxy) alkane anhydrides] and a selection of co-polymers of sebacic/ [bis(p-carboxyphenoxy) propane anhydride] P(SA-CPP). The techniqe is compared to conventional infrared for characterisation work, highlighting the advantage of small sample requirement and minimal sample preparation necessary for acquisition of spectral information. It is possible to differentiate between aromatic and aliphatic anhydride bonding, and in conjunction with other diagnostic bands to monitor the change in individual monomer composition within a co-polymer mixture.     

Conformational study of (R)-(+)-limonene in the liquid phase using vibrational spectroscopy (IR,Raman, and VCD) and DFT calculations

A conformational study in the liquid phase of the terpene (R)-(+)-limonene has been carried out, revealing the presence of three conformers. For this task, experimental vibrational techniques, such as IR, Raman, and VCD spectroscopies, together with quantum chemical calculations, have been used. Our study reveals that a previous vibrational analysis is desirable to achieve a thorough analysis of the VCD spectrum as well as that these three experimental techniques are complementary to characterize flexible systems, which present several conformers.