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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. [ABSTRACT FROM AUTHOR]

Freeze- and spray-dried inclusion complexes (ICs) of chlorhexidine (CHX) in β-cyclodextrin were characterized by Fourier transform (FT)-Raman, 1H nuclear magnetic resonance (NMR), and photoacoustic spectroscopy. The active Raman modes of CHX were simulated using the density functional theory. By considering semiempirical calculations, it was observed that the guest penetrates on the wider rim of the host in a proportion of 1:2. We observe from the FT-Raman analysis that the drying method influences the CHX:β-cyclodextrin conformational adjustment by the rearrangement of hydrophilic biguanides of the guest. The photoacoustic spectroscopy results inferred that the freeze-drying method provided a better inclusion due to a lower interaction between phenyl groups and hexamethylene of CHX. The freeze-dried IC achieved a faster dissolution pattern. These ICs provided immediate drug dissolution profiles in an aqueous medium better than a pure drug. The release profiles of freeze- and spray-dried ICs were explained by Fickian diffusion. These data support further planning and development projects of novel immediate release systems based on CHX. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance is a challenging health problem that demands alternative treatments. Nanoplatforms with antimicrobial properties, associated with photodynamic and photothermal therapies, are potential candidates for this task due to characteristics such as non-invasive, antibiotic-free, dual selectivity, and low adverse effects in therapeutic procedures. Graphene quantum dots are a possible substitute for other nanoparticles, especially by presenting low toxicity and low cost. However, graphene quantum dot properties are highly dependent on the synthesis methods, which makes it difficult to compare and improve methods using different studies. In this work, we apply spectroscopic and photothermal methods to investigate a commercially available green fluorescent graphene quantum dot (GQD) as a potential antimicrobial agent and to determine its theranostics properties. The results showed that the photoactivation of the GQD in phosphate-buffered saline solution by light sources with wavelengths shorter than the emission band can generate singlet oxygen and a heat yield of 50 % under excitation at 532 nm, showing the potential of this GQD as a photodynamic and photothermal agent. [ABSTRACT FROM AUTHOR]

Thermal lens spectrometry has been utilized in various applications, and in some application areas, high sensitivity is required. In this work, a mode-mismatched thermal lens configuration probing thermal lens twice was developed for sensitivity enhancement. Experimental results exhibited that doubled sensitivity was achieved with this configuration compared with that attained with a conventional one, which was consistent with the prediction of the theoretical model for thermal lens spectrometry. As a result of the consistency, the linear absorption (attenuation) coefficient of de-ionized water at 532.3 nm was directly measured with this configuration and the conventional one and found to be (4.90 ± 0.05) × 10−2 m−1 and (4.7 ± 0.2) × 10−2 m−1, respectively. The results are in good agreement with accepted literature values. Theoretical analysis revealed that the sensitivity enhancement with this configuration is greater than that by simply doubling the sample thickness in a conventional configuration. [ABSTRACT FROM AUTHOR]

Alternative fuels hold considerable promise as substitutes for petroleum diesel fuel. As such, biodiesel is a promising renewable fuel that has been developed and tested by a number of research groups. Quality control of this transportation fuel is of great significance to its commercialization. Conventional chromatographic and spectroscopic analytical methods are most commonly used for biodiesel characterization, in some cases yielding information detail beyond that needed for the determination of biodiesel quality. By contrast, less common methods, such as photothermal techniques, are well suited to characterize a wide range of transportation fuels. The complexities of photothermal and chemical analytical techniques are roughly similar, as are the costs. Photothermal methods are based on spectroscopic and thermophysical properties of the sample, an advantage with respect to ordinary chromatography and spectroscopy techniques. Furthermore, some photothermal techniques can be adapted for remote signal detection, which can be used for in situ analysis in fuel production for inline biodiesel quality inspection and control. Therefore, an overview and outlook of the photothermal characterization is of considerable interest. In this paper, the applications of photothermal techniques in the characterization of biodiesel, petroleum diesel fuels, and their blends are reviewed. The review includes thermophysical properties and correlations for fuels, determination of blend levels, and biodiesel stability investigations. After the review, discussion and perspective are presented for future improvement of photothermal characterization and industrial applications. [ABSTRACT FROM AUTHOR]

Analytical and finite element analysis modeling methods of the pulsed-laser excited photothermal (PT) lens signal of solids samples surrounded by air are presented. The analytical and finite element analysis solutions for the temperatures induced in the sample and in the air were found to agree over the range of conditions in this report. Model results show that the air contribution to the total PT lens signal is significant in many cases. In fact, these solutions open up the possibility of applying the pulsed excited thermal lens method for accurate prediction of the heat transfer to the coupling fluid and subsequently to study the gas surrounding the samples by using a known material solid sample. [ABSTRACT FROM AUTHOR]

This paper presents an improved theoretical description of the mode-mismatched thermal lens effect using models that account for heat transport both within the sample and out to the surrounding coupling medium. Analytical and numerical finite element analysis (FEA) solutions are compared and subsequently used to model the thermal lens effect that would be observed using continuous laser excitation. FEA model results were found to be in excellent agreement with the analytical solutions. The model results show that heat transfer to the air coupling medium introduces only a minor effect when compared with the solution obtained without considering axial air-sample heat flux for practical examples. On the other hand, the thermal lens created in the air coupling fluid has a relatively more significant effect on the time-dependent photothermal lens signals. [ABSTRACT FROM AUTHOR]

In the present work, we use an open-photoacoustic-cell (OPC) operating at high frequency to measure thermal properties of two-layer system samples. Photothermal deflection technique is also employed to measure the samples. The effective thermal diffusivity measured using the OPC method is interpreted using the concept of effective thermal resistance for a series two-layer system. The results show the reliability of the photoacoustic method for a complete thermal characterization of the samples. In addition, by varying the sample effective thickness, the thermal diffusivity and conductivity of each layer are precisely determined. The effective thermal diffusivity, thermal conductivity, and specific heat of a porous catalyst layer (thickness varying from 13 to 53 μm) deposited on an aluminum foil (53 μm in thickness) were thus measured and found to be (3.7±0.3)×10-3 cm2/s, (7.5±0.7)×10-3 W/cm K, and (1.6±0.2) J/gK, respectively. [ABSTRACT FROM AUTHOR]

We applied the open photoacoustic cell method operating at high frequency as an efficient and highly precise tool for the measurement of thermal properties of rubberized two-layer systems. The heat-coupling between the two layers is treated using the analogy between thermal and electrical resistances widely used in heat transfer problems. The thermal resistance between the two layers is considered effective and the problem is decoupled for each layer. Measurements are performed in two-layer samples of aluminum foil coated with layers of rubberized paint with different thicknesses. Thermal diffusivity and thermal conductivity are determined for the paint. The results are retrieved from the thermal resistance model assuming the effective thermal diffusivity of the composite material. [ABSTRACT FROM AUTHOR]

Recent improvements in the modeling of photo-induced thermo-optical-mechanical effects have broadened the application of photothermal techniques to a large class of solids and fluids. During laser excitation, changes in optical reflectivity due to temperature variation may affect the photothermal signal. In this study, the influence of the reflectivity change due to heating is analyzed for two pump-probe photothermal techniques, thermal lens and thermal mirror. A linear equation for the temperature dependence of the reflectivity is derived, and the solution is tested using optical properties of semitransparent and opaque materials. For semi-transparent materials, the influence of the reflectivity change in photothermal signals is less than 0.01%, while for opaque materials it is lower than 3%. [ABSTRACT FROM AUTHOR]

Photodynamic Therapy (PDT) is a powerful technique for the treatment of cancer and non-cancerous diseases. The precise PDT treatment protocol definition must consider the performance difference between in vitroand in vivoapplications. This also occurs in other biological studies, and to partially overcome this difficulty, the simulated body fluids are generally applied as a prior understanding of the particularities of the different systems. However, in PDT these studies are scarce. In this work, we investigated the photoactivation of Erythrosine, a photosensitizer widely used in PDT, in different simulated body fluids. Differences in the photodegradation kinetics, triplet lifetime, and singlet oxygen generation were observed. The results can help to explain and to define PDT application protocols., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Laser-induced wavefront distortion is detectable by several techniques based on the photothermal effect. The effect is probed by monitoring the phase shift caused by the bulging of the heated area, the photoelastic effects, and the spatial distribution of the refractive index within the sample and in the fluid surrounding it. A simple analytical solution for the wavefront distortion was only possible for low absorbing materials, with the assumption that the stresses obey either the thin-disk or the long-rod type distributions. Recently, a unified theoretical description for the laser-induced optical path change was proposed to overcome part of this limitation for weakly absorbing materials, regardless of its thickness. In this work, we perform an experimental investigation taking the sample-fluid heat coupling effect into account using the thermal lens technique. The experimental investigation presented here validates the unified model. In addition, we show that the heat-coupling model provides an alternative method to obtain physical properties of non-absorbing fluid by using a reference solid sample.

We propose a combined thermal lens and thermal mirror method as concurrent photothermal techniques for the physical characterization of polymers. This combined method is used to investigate polymers as a function of temperature from room temperature up to 170 °C. The method permits a direct determination of thermal diffusivity and thermal conductivity. Additional measurements of specific heat, linear thermal expansion, and temperature-dependent optical path change are also performed. A complete set of thermal, optical, and mechanical properties of polycarbonate and poly (methyl methacrylate) samples are obtained. Methods presented here can be useful for in situ characterization of semitransparent materials, where fast and non-contacting measurements are required.