In Situ Imaging of Barnacle (Balanus amphitrite) Cyprid Cement Using Confocal Raman Microscopy

Barnacles are a model for research on permanent underwater adhesion and the wider process of marine biofouling. A detailed understanding of the permanent adhesive secreted by the cypris larva for permanent settlement, the so-called cyprid cement, has potential to lead to novel antifouling solutions. There is a need for micro-analytical chemical in situ methods to gain more insight into the process of adhesion and the chemical composition of the cement. In this study, the applicability of confocal Raman microscopy for imaging the cyprid cement beneath permanently attached juvenile barnacles (Balanus amphitrite) was explored. Based on acquired area scans Raman images for characteristic chemical functional groups were obtained. In addition to showing the morphology of the attachment apparatus, the images provided information on chemical composition, in particular the hydration state of the cement, and demonstrated the potential of this method for in situ studies of adhesion at the micro-scale.     

Confocal Raman microscopy study of the melamine distribution in polyester–melamine coil coating

Hexamethoxymethylmelamine, a common crosslinker used in combination with polyester resins to prepare thermosetting coatings, can self-condense during curing and in theory build up regions with high crosslink density (melamine enrichment). This distribution may affect such properties as the “local” glass transition temperature and structural heterogeneity and thereby modify formability, stain resistance, and weatherability. The self-condensation regions have not previously been observed in detail so their distribution in the film is unclear. Confocal Raman microscopy (CRM) has been used to characterize the melamine distribution in three polyester–melamine paint systems: one clear and two pigmented coil coatings. Both the surface mapping and depth profiling features of CRM were used to perform a 3D analysis. The depth profiling of the clear coating was performed in a nondestructive way, but due to the opaque nature of the pigments, cross sections of the pigmented coatings were prepared in order to facilitate the analysis of the melamine distribution through the film thickness. Melamine-enriched zones were found on the surfaces of all three samples. They appeared to be approximately spherical with diameters of around 5 μm. It was also observed from the cross sections that the melamine-enriched zones appeared as “particles” distributed randomly through the coating. The Raman spectra collected at these regions show significantly higher triazine ring band intensity. All of these findings confirm the hypotheses constructed over the past 20–30 years. This paper was awarded Second Place in the 2008 FSCT Roon Awards competition held as part of the FutureCoat! conference sponsored by the Federation of Societies for Coatings Technology, in Chicago, IL, on October 14–16, 2008.     

Single Cell Confocal Raman Spectroscopy of Human Osteoarthritic Chondrocytes: A Preliminary Study

A great deal of effort has been focused on exploring the underlying molecular mechanism of osteoarthritis (OA) especially at the cellular level. We report a confocal Raman spectroscopic investigation on human osteoarthritic chondrocytes. The objective of this investigation is to identify molecular features and the stage of OA based on the spectral signatures corresponding to bio-molecular changes at the cellular level in chondrocytes. In this study, we isolated chondrocytes from human osteoarthritic cartilage and acquired Raman spectra from single cells. Major spectral differences between the cells obtained from different International Cartilage Repair Society (ICRS) grades of osteoarthritic cartilage were identified. During progression of OA, a decrease in protein content and an increase in cell death were observed from the vibrational spectra. Principal component analysis and subsequent cross-validation was able to associate osteoarthritic chondrocytes to ICRS Grade I, II and III with specificity 100.0%, 98.1%, and 90.7% respectively, while, sensitivity was 98.6%, 82.8%, and 97.5% respectively. The overall predictive efficiency was 92.2%. Our pilot study encourages further use of Raman spectroscopy as a noninvasive and label free technique for revealing molecular features associated with osteoarthritic chondrocytes.     

Estimation of the surface interaction mechanism of ZnO nanoparticles modified with organosilane groups by Raman Spectroscopy

We investigated the surface modification of zinc oxide nanoparticles (ZnO-NPs) with 3-aminopropyltriethoxysilane (APTES). The ZnO-NPs were synthesized by the physical method of continuous arc discharge in controlled atmosphere (DARC-AC). The surface modification was performed using a chemical method with constant stirring and reflux for 24 h at room temperature. This surface functionalization of the ZnO nanoparticles (funct-ZnO-NPs) was experimentally confirmed by infrared spectroscopy (FT-IR), Raman spectroscopy, TGA, UV–Visible and XRD, while its morphological characterization was performed by HRTEM. Using Raman spectroscopy, it was possible to study the functionalization process after the change, as well as the appearance of new bands of the molecular vibrations produced by the chemical interaction of the surface of the nanoparticles with the silane coupling agent. Comparing the Raman spectra of the ZnO-NPs, APTES and funct-ZnO-NPs, it was observed that the area between 2700 and 3200 cm⁻¹ related to the vibrations of the CH₂ and CH₃ bonds of the APTES molecule. The funct-ZnO-NPs showed a decrease in the peak intensity, which indicates a deactivation of the degrees of freedom of the APTES at the time of the surface functionalization with the ZnO-NPs, suggesting a redistribution of the APTES CH₂ groups, as they interact with the surface of the ZnO-NPs. The APTES molecule is anchored to the surface of the ZnO-NPs via one or two Si-O-Zn bonds and not by three, as is commonly reported. The above finding is attributable to steric impediment of the side groups of the APTES and the strain of the Si-O-Zn bonds that hinders the trivalent interaction with the surface of the nanostructured ZnO. Similarly, the results obtained by Raman were verified and complemented by means of FT-IR due to the presence of bands at specific wavelengths.     

In Situ Ultraviolet Raman Study on the Phase Transition of Hafnia up to 2085 K

We have recently demonstrated that the Raman scattering through ultraviolet (UV) excitation is eminently well suited for in situ investigation of materials at high temperatures up to 1773 K. Here we report successful Raman measurements of HfO₂ up to 2085 K, using only a 100 mW power of UV laser line. The monoclinic-to-tetragonal transformation finished around 2080 K on heating, while the monoclinic phase appeared at 2018 K on cooling.     

Measurement of Concentration Profiles in Thin Film Binary Polymer-Solvent Coatings Using Confocal Raman Spectroscopy: Free Volume Model Validation

Concentrations of solvent and polymer have been measured using confocal Raman spectroscopy in poly(styrene)-tetrahydrofuran, poly(methyl methacrylate)-tetrahydrofuran, and poly(styrene)-p-xylene systems. Free volume theory parameters have been regressed from the measured concentration data. Model-predicted concentration profiles are in very good agreement with the measured profiles in the case of a highly volatile solvent. For instance, free-volume-model-predicted profiles are in very good agreement in poly(styrene)–tetrahydrofuran system and poly(methyl methacrylate)–tetrahydrofuran system. However, the free volume model is not able to predict entire measured profiles in the case of less-volatile solvent in poly(styrene)–p-xylene system.     

Measurements of Concentration Profiles in Polymeric Solvent Coatings by Means of an Inverse Confocal Micro Raman Spectrometer—Initial Results

Concerning quality and drying time of a process the key issue is the progression of the concentration profiles within the film during drying. This contribution reports on the development of a new measuring technique, an Inverse-Confocal-Micro-Raman-Spectrometer, for online measurements of concentration profiles during drying in thin (5-200 µm) polymeric solvent coatings. The spatial and temporal resolution of the measurements is up to one micron and one second. A calibration method has been developed by taking Raman spectra of different, precisely concentrated samples in sealed quartz glass cells and by calculating the ratio of the intensities of the characteristic Raman peaks. The accuracy of this basic calibration method is very good over a wide concentration range. Initial investigations were carried out on the polymer solvent systems: polyvinyl acetate(PVAc)-toluene, PVAc-methanol, PVAc-benzene, and PVAc-methanol-toluene, PVAc-methanol-benzene.     

Effect of hydrogen on the UV Raman intensities of diamond-like carbon

UV Raman spectroscopy is a powerful technique for the investigation of diamond-like carbon (DLC) films because it can provide information on the density, mechanical and optical properties.Here we show a detailed analysis of the G and D peak Raman intensity of hydrogenated DLC (a-C:H) with hydrogen (H) content ranging from 25 to 50 at.%. We show that the G peak Raman intensity strongly increases with the H content. This has been attributed to a strong enhancement of the UV Raman cross-section with the H incorporation.     

Study of the porous structure of white chocolate by confocal Raman microscopy

Confocal Raman microscopy has been shown to be a useful technique for investigation of white chocolate surfaces. The appearance of protrusions and pores, and the distribution of fat, sucrose, and milk powder at and below the surface of white chocolate pralines were investigated using confocal Raman microscopy. Raman horizontal and depth scans showed that the protrusions and pores continue at least 10 µm into the chocolate shell and that some protrusions and channels mainly consist of fat, while some consisted of a fat layer, leaving a hollow space underneath. Further, the pores and their continuing channels consisted of nothing but air. These findings indicate that the protrusions might be connected to channels where we suggest a pressure driven convective flow of liquid fat from within the chocolate matrix that, depending on temperature, moves up to the surface or goes back into the matrix, leaving an empty pore with a shell of fat at the surface, which in some cases collapse and leaves a hollow pore and channel. Therefore, these findings support that the protrusions could be connected to oil migration in chocolate and, thus, further to fat bloom development. Practical applications: Confocal Raman microscopy can be used to investigate the local distribution of different components in white chocolate. This technique offers the possibility to acquire the local distribution of different components within the sample, with a resolution down to the optical diffraction limit. Further, the analysis can be performed at ambient conditions, without requiring any special sample preparation or marker molecules. The results obtained by using this technique suggest that specific surface imperfections on chocolate could be part of a network of pore structures at and beneath the chocolate surface, which could be related to oil migration and thus, to fat bloom formation.     

Depth profiling of clear coil coating by confocal Raman microscopy

Confocal Raman microscopy (CRM) has been demonstrated to be very effective in the analysis of the distribution of chemical moieties within polymeric coil coatings. To verify the compatibility of CRM with commercial coil coatings, a multi-layer coil coating system was prepared and depth profiled by CRM with both dry and immersion oil objectives (non-destructive method). The cross-section of the same sample was then scanned by CRM (destructive method). It was found that the CRM depth profiling resolution was affected by both the intrinsic and extrinsic factors of the objective lens. The use of an immersion oil objective improved depth resolution and minimised the refraction effect, however the oil contaminated the coating surface. The dry method yielded the lowest depth resolution but was completely non-destructive. The CRM lateral scanning of the sample cross-section yielded the most accurate depth profile information; however, the destructive nature of this method is a major disadvantage. It was also found that pigments incorporated in the coil coating formulation affected the CRM depth profiling accuracy due to the strong Raman scattering of these materials.     

Raman Study of the Interface between Hot-Pressed Silica Parts

We present a Raman spectroscopy study of silica glasses prepared by hot-pressing of gels. Our particular interest is the structure at the interfaces formed during hot-pressing of small parts to obtain large pieces, such as silica tubes for optical-fiber preforms. A specific feature of the interface that distinguishes this layer from the bulk is its fractal structure. The parameters of the fractal units, including their maximum dimensions in real space, are determined by the pre-hot-pressing mechanical processing. We attribute this structure to residual microcracks inherent in the surface layer of polished plates. There are no fractals at the interfaces sintered at temperatures higher than the glass transition temperature.     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.     

Wetchemical surface modification of plasticized PVC. Characterization by FTIR-ATR and Raman microscopy

The chemical modification of plasticized PVC films with amino thiophenol in mixtures of DMF/H₂0 has been studied. The degree of modification and the distribution of modified groups within the films were determined using Raman spectroscopy and FTIR-ATR. The amounts of plasticizer (bis-2-ethylhexyl phtalate, DOP) bleached out during the reaction and the amount of dimethylformamide (DMF) penetrated into the film were analysed in control reactions without the reactant using ¹H NMR spectroscopy and Raman spectroscopy.Reaction kinetics and surface selectivity of the modification reaction were compared with the corresponding reactions of PVC films without plasticizer.     

Determination of Deterrent Profiles in Nitrocellulose Propellant Grains Using Confocal Raman Microscopy

The diffusion profile of dinitrotoluene deterred nitrocellulose based small arms propellants is investigated with Confocal Raman microscopy. The diffusion profile in all samples was found to be non‐Fickian Case II diffusion – a steady concentration with a sharp drop. Diffusion depth from the outside surface was found to be much greater than the interior perforation surface. A strong correlation was found between the perforation size of samples and their inside edge diffusion depth, while the outside surface was found to be more dependent on total diameter and deterrent concentration. Samples were also artificially aged to investigate movement of the deterrent over time.     

Experimental and theoretical Raman study on the structure and microstructure of Li0.30La0.57TiO3 electrolyte prepared by the sol-gel method in acetic medium

In this report, we prepare LLTO ceramics by the sol-gel method in acetic medium. Raman spectroscopy showed the formation of lanthanum and titanium acetates precursors, which after calcination, lead to formation of the LLTO nanoparticles. Raman spectra were scanned directly over the LLTO pellets and the disappearance of impurities was observed during the microstructure evolution with increasing sintering temperature. X-ray diffraction characterization, including full pattern profile fitting refinements, showed no drastic changes in the unit cell parameters of the LLTO perovskite, but a large increase in the crystallite size domain was observed with increasing sintering temperature. Additionally, an interesting structural phase transition for the Li_0.30La_0.57TiO₃ perovskite structure was observed, from tetragonal P4/mmm to distorted-cubic Pm-3m spacegroup, for the highest sintering temperature (Ts=1300 °C). Experimental and theoretical simulations of Raman spectroscopy confirmed the formation of a distorted-cubic phase and confocal Raman spectroscopy showed the presence of traces of impurities at the grain boundary region. In spite of the low total lithium conductivity observed, the electrochemical impedance spectroscopy analysis showed a remarkable increase in the lithium bulk conductivity for Ts=1300 °C. This fact could be attributed to the structural phase transition from tetragonal to the cubic crystal system.     

In Situ Raman Spectroscopic Study of Yttria-Stabilized Zirconia Attack by Molten Sodium Vanadate

Raman spectroscopy has been used to study the molten salt attack of ceramics used as thermal barrier coatings. Zirconia stabilized with 8 wt% yttria was immersed in sodium metavanadate melts and in sodium metavanadate/sodium sulfate melts. In situ Raman measurements allowed simultaneous observation of the ceramic phases and salt chemistry during the attack process. The ceramic was seen to transform from the cubic/tetragonal to the monoclinic phase, concurrent with chemical changes in the molten salt layer in contact with the ceramic. These in situ measurements were complemented by conventional postexposure examination and by postexposure Raman measurements. The rate of attack was found to be quite sensitive to the mole fraction of vanadate in the molten salt solution.     

Non-destructive 3-dimensional mapping of microcapsules in polymeric coatings by confocal Raman spectroscopy

Nowadays, the properties of polymeric coatings are enhanced by various additives mixed into the resin. Recently, embedding of polymeric microcapsules into the coating matrix has been investigated to provide special on-demand features to the coating. The detection and characterization of such microcapsules in a polymeric coating are of major importance but difficult, because both are built up by similar molecules with similar densities. Current analysis methods require complex sample preparation to allow reliable measurements.In contrast, confocal Raman spectroscopy allows fast and non-destructive differentiation between characteristic molecular bonds at a spatial resolution below one micrometer. Hence, the objective of this research was to apply this technique on microcapsules embedded in a coating and provide answers to the following questions: Can one detect microcapsules embedded in a coating and clearly identify them? Can one differentiate between full and empty microcapsules and the coating matrix? Can one determine the exact location of the capsules and their distribution in the coating?Therefore, several two-dimensional confocal Raman spectroscopy mappings recorded at different depths allowed a three-dimensional reconstruction of the polymeric coating with the polymeric microcapsules in it. Thereby, the distribution of the capsules within the coating could be determined with micrometer resolution. As a result Raman tomography provides a more detailed insight into the distribution of microcapsules through the possibility of three-dimensional reconstruction.     

Erratum: Determination of Deterrent Profiles in Nitrocellulose Propellant Grains Using Confocal Raman Microscopy

Due to a technical error this article was published online with two DOI: (10.1002/prep.201000081 and 10.1002/prep.201100081). When citing or referring to this article, please use the following DOI: 10.1002/prep.201000081.     

The application of Raman spectrometry to investigate and characterize cement, Part I: A review

Raman spectrometry has received attention for the past 3 decades in its application to the characterisation of pure cement phases, white and grey cements. Various configurations of instrumentation and laser excitation sources have been used, as reported in a limited number of papers. The first demonstrated investigation in 1976 by Bensted, illustrated the characterisation of various pure mineral cement phases with the use of a visible excitation source and a standard dispersive configuration. This was soon followed by an investigation of pure phases, as well as white and grey cements in 1980 by Conjeaud and co-workers using a microprobe configuration and visible excitation. Considerable difficulties with excessive fluorescence phenomena, especially with grey cements, have however been reported from the initial to the most recent publication. This review aimed to report on Raman studies of pure synthesized cement phases, cement phases as found in white and grey cements, various forms of gypsum and related compounds as found in cement and concrete, hydration of pure cement phases, as well as those of white and grey cement and lastly carbonation effects. Results reported are discussed and tables of summarized observed Raman shifts are given.     

A comparison of different approaches for depth profiling of films and coatings by confocal Raman microscopy

We compare and analyze different approaches to perform depth profiling of polymer films and coatings by confocal Raman microscopy (CRM). Data were generated using three methodologies: conventional metallurgical objectives, oil-immersion optics and numerical post processing of the as-measured intensity profiles, via an optimized deconvolution technique adapted to CRM. A series of bi- and multi-layered polymeric films were used as test systems. Strengths and weaknesses of each methodology are evaluated in terms of delivered depth resolution, signal throughput and flexibility. It is shown that the application of regularized deconvolution on data obtained from dry objectives yielded intensity profiles with a quality comparable, in some cases superior, to those obtained with immersion objectives, with the advantage of being totally non-invasive.