Although the topography of van de Waals (vdW) layers and heterostructures can be imaged by scanning probe microscopy, high-frequency interface elastic properties are more difficult to assess. These ...can influence the stability, reliability, and performance of electronic devices that require uniform layers and interfaces. Here, we use picosecond ultrasonics to image these properties in vdW layers and heterostructures based on well-known exfoliable materials, i.e., InSe, hBN, and graphene. We reveal a strong, uniform elastic coupling between vdW layers over a wide range of frequencies of up to tens of gigahertz (GHz) and in-plane areas of 100 μm2. In contrast, the vdW layers can be weakly coupled to their supporting substrate, behaving effectively as free-standing membranes. Our data and analysis demonstrate that picosecond ultrasonics offers opportunities to probe the high-frequency elastic coupling of vdW nanolayers and image both “perfect” and “broken” interfaces between different materials over a wide frequency range, as required for future scientific and technological developments.
Non-invasive fast imaging of grain microstructure of polycrystalline ceria with sub-micrometric spatial resolution is performed via time-domain Brillouin scattering. The propagation of a nanoacoustic ...pulse is monitored down to 8 μm deep in a 30 × 30 μm2 area. Grains boundaries are reconstructed in three-dimensions via a two-step processing method, relying on the wavelet synchro-squeezed transform and the alphashape algorithm. Imaging contrast is improved by taking advantage of stronger sensitivity to anisotropy of transverse acoustic waves, compared with longitudinal waves. Utilization of transverse waves in the image processing reveals additional boundaries, confirmed by an electron backscattering diffraction pattern but not discerned using longitudinal waves. A buried inclined interface between differently oriented grains is identified by monitoring changes in amplitude (phase) of the portion of the signal associated with transverse (longitudinal) waves. Estimates of the inclination angle of this interface prove the sensitivity of our laser ultrasonic method to image inclined boundaries.
This work aimed to investigate and compare the composition and the physicochemical properties of 18 different sources of edible vegetable oils. A systematic study on the correlation between ...composition and physical properties was performed using Fourier Transform Infrared (FTIR) Spectroscopy and fatty acid chromatographic analysis. Principal component analysis of FTIR spectra is performed to classify edible oils concerning their physical properties. The results demonstrate the potentiality of the method associated with multivariate statistics analysis as powerful, fast, and non-destructive tools for characterization and quality control of edible vegetable oils.
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•The correlation of composition and physicochemical properties of edible vegetable oils•Chromatographic and spectroscopic techniques associated with multivariate statistics analysis•Unsaturated fatty acids are related to mass density, dynamic viscosity, oxidative stability index and refractive index.•These techniques allow predicting oil properties, helping in the characterization and quality control of vegetable oils.•Direct correlation of the PCA components with the set of information about composition and physical properties of the oils
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•Thermal stability discrimination of biodiesel by thermal lens spectroscopy.•Induction of photochemical reaction and thermal diffusion on biodiesel.•Induction processes are carefully ...accounted for theoretically and experimentally.•Effects of photoreaction time and mass diffusion on biodiesel are studied.•Photobleaching cross-section and thermal yield are determined.
Recent studies on laser induced thermal lens effect has made it possible to use this tool to investigate thermo-physical and chemical properties of biofuels. During laser illumination, a number of light induced effects may take place in the excited volume of the sample. However, the complexity of information included in the thermal lens transients could lead to misinterpretation of the results. This work examines the theoretical and experimental aspects that must be considered when performing biodiesel analysis using thermal lens spectrometry. The induction of photochemical reaction and thermal diffusion processes is carefully accounted for by describing the localized optical path change due to the concentration gradient created within the sample. We characterize mechanical, chemical and photochemical properties of thermal degraded biodiesels, enabling quantitative access of mass diffusion coefficient, photobleaching cross-section, and thermal yield. Dynamic viscosity analysis corroborates the results obtained by thermal lens, describing the method as very sensitive to thermal stability discrimination of biodiesel.
Biodiesel susceptibility to oxidation is one of the major problems concerning its use as an alternative to diesel fuel. Although well-characterized, the oxidation process cannot be completely ...prevented since it can be affected by a large number of factors, such as fuel composition, storage conditions, contaminants, temperature, and the presence of air and light. In this work, we propose Fourier transform infrared spectroscopy (FTIR) in association with principal components analysis (PCA) and hierarchical cluster analysis (HCA) as a method for monitoring the extent of oxidation degree of biodiesel in the low rate phase, before the end of the induction period, in which the changes in the physical properties such as viscosity, mass density, and chain composition of the sample remain almost undetectable. A detailed investigation of thermo-oxidation of biodiesel is reported for a mixture of 50/50 (%) of soybean oil and animal fat biodiesels. The biodiesel degradation was accelerated when maintaining the temperature of the sample at 110 °C under constant air flux for different times. Oil stability index, mass density, viscosity, gross caloric value, esters composition, UV–vis, and FTIR spectra were measured in order to analyze the degree of degradation of each sample. The multivariate analysis in the FTIR spectra clearly shows the discrimination of the samples in the first stage of the degradation process. These results could be useful as a method for monitoring the fuel quality during storage, helping fuel producers, suppliers, and users.
The international public health emergency related to COVID‐19 caused by the SARS‐CoV‐2 virus has altered several production and registration criteria for sanitary products, including alcohol‐based ...hand sanitizers. In this work, we investigate the concentration of alcohol in sanitizers presented in gel form applying the principal component regression method on measurements using Infrared and Raman spectroscopic methods. The chemometric calibration is performed using isopropanol or ethanol as active agents, and the method is used to characterize several commercial samples. Furthermore, the results of the prediction of alcohol concentration, obtained by applying the principal component regression and partial least squares methods, in the spectroscopic techniques, were compared with each other and with the results provided by nuclear magnetic resonance. Our results show that spectroscopic techniques coupled with principal component regression are fast, low‐cost, and safe tools for the determination of alcohol concentration, regardless the gelling agent used.
The association between chemometrics and spectroscopy in the determination of alcohol in sanitizing products in the form of a gel allows for a quick, low‐cost measurement without subjective treatment of the spectroscopic analysis results.
Abstract Edible vegetable oils are sources of polyunsaturated fatty acids, necessary for a balanced diet capable of providing elements that act on the energetic, structural, and hormonal composition ...of humans. The growing consumption of these foods has encouraged the search for techniques capable of characterizing their compositions and transformations when subjected to industrial processes or during domestic use. We propose to analyze the transformations undergone by edible vegetable oils originating from different plants due to thermal oxidation. For this, dynamic viscosity, oxidative stability index, fatty acid profile, and infrared spectra determined before and after being subjected to thermal oxidation. The results from infrared spectroscopy were improved through Principal Component Analysis (PCA). Among other results, it was possible to establish correlations between the FTIR spectra, dynamic viscosity, and the profile of fatty acids, allowing the prediction of the concentration of polyunsaturated fatty acids (PUFA) after thermal oxidation by measuring the spectrum of samples before the thermal oxidation process. Furthermore, it is observed that the dynamic viscosity is strongly altered by thermal oxidation, which is directly related to the decrease in PUFA content. The results obtained can be used to predict quality factors of edible vegetable oils, helping to choose the right type of oil for each industrial or domestic process. Practical Applications : This research holds significant practical implications, particularly in detecting adulteration and fraud of edible vegetable oils. The developed method uses physicochemical properties and infrared spectroscopy with principal component analysis to characterize oils and to determine the oil stability index.
Picosecond laser ultrasonics is an experimental technique for the generation and detection of ultrashort acoustic pulses using ultrafast lasers. In transparent media, it is often referred to as ...time-domain Brillouin scattering (TDBS). It provides the opportunity to monitor the propagation of nanometers-length acoustic pulses and to determine acoustical, optical, and acousto-optical parameters of the materials. We report on the application of TDBS for evaluating the effect of Praseodymium (Pr) substitution on the elasticity of multiferroic (Bi1−xPrx)(Fe0.95Mn0.05)O3 (BPFMO) thin films. The films were deposited on Si and LaAlO3 (LAO) substrates by a sol-gel method. X-ray diffraction and Raman spectra revealed earlier that a phase transition from rhombohedral to tetragonal structure occurs at about 15% Pr substitution and is accompanied by the maxima of remnant magnetization and polarization. Combining TDBS with optical spectral reflectometry, scanning electron microscopy, and topographic measurements by atomic force microscopy, we found that the structural transition is also characterized by the maximum optical dielectric constant and the minimum longitudinal sound velocity. Our results, together with earlier ones, suggest that BiFeO3-based films and ceramics with compositions near phase boundaries might be promising materials for multifunctional applications.
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