Open Photoacoustic Cell Technique Research Articles

Thermal and optical characterization of rhodamine 6G doped silica-glasses

In heat-exchange applications, glasses with excellent heat transfer characteristics are essential. In this study, different concentrations of Rhodamine 6G (Rh6G) doped silica glasses were synthesized using the sol–gel method, and their thermal effusivities were measured and compared. The samples are structurally identified using the X-ray diffraction (XRD) technique. Using a UV–Vis spectrophotometer, the optical absorption spectra (in the range of 300–900 nm) of the intrinsic as well as Rh 1 × 10−4 M and Rh 1 × 10−3 M doped silica samples were recorded, which showed a peak centred at 500 nm for both the rhodamine doped silica samples and Fourier transform infrared (FTIR) spectroscopic techniques, that indicates modification of lattice due to presence of Rh6G. An increase in absorption with a concentration of Rh6G was observed from the optical absorption spectrum. Open cell photoacoustic technique was used for the Photoacoustic (PA) studies. The thermal effusivity values obtained increase with the doping concentration of Rhodamine 6G (maximum value of 2.298 × 103 Ws1/2 K−1 m−2 corresponding to 1 × 10−3 M).

Fractional dual-phase-lag heat conduction with periodic heating and photo-thermal response

We apply an extension of dual-phase-lag in thermal systems to predict the photoacoustic signal for transmission configuration and characteristics of the open photoacoustic cell technique. For this, we consider a particular case from Jeffrey?s equation as an extension of the generalized Cattaneo equations. In this context, we obtain the temperature distribution under the effects of fractional differential operators, allowing the calculation of the Photoacoustic signal for the transmission set-up. The results show a rich class of behaviors related to the anomalous diffusion connected to these fractional operators.

Generalized thermoelastic effect in real metals and its application for describing photoacoustic experiments with Al membranes

A generalized theoretical model of the formation of a thermoelastic photoacoustic signal from real materials is proposed taking into account the presence of defects and impurities. An effective coefficient of thermal expansion was introduced that describes the dilatation effect of thermally activated lattice irregularities. Expressions for the thermoelastic photoacoustic signal obtained in the linear approximation were applied to describe aluminum membrane vibrations at the periodic laser excitation measured in other studies using a gas-microphone open-cell photoacoustic technique. The proposed theoretical model allows us to explain the experimental results in the 20 Hz–7 kHz modulation frequency range without invoking the assumption of the bulk absorption of pump laser radiation in aluminum membranes.

Photoacoustic Spectroscopy for Curing Time Determination of an Acrylic Nanocomposite

Photoacoustic spectroscopy (PAS) has been widely used as a nondestructive and sensitive analytical technique used to determine the thermal diffusivity, effusivity and heat capacity of different materials. In this work, the open cell photoacoustic technique (OPC) technique was used for the kinematic study of heat transfer processes as a function of time for curing nanoresin composites. An exponential growth of the signal during the process of curing was observed. The nanoresin was based on silver nanoparticles (AgNPs) that were synthesized using a green method from an aqueous extract of Capsicum annuum var annuum as an Ag reducer and an acrylic resin. It was cured using a violet laser beam with a wavelength of 405 nm with an average power of 120 mW. The characteristic curing time was measured as a function AgNPs concentration of 0.0, 5.16, 7.27, 11.85, 14.50, 16.86 and 20.96 × 10−4 vol%. The results showed an increase in the curing time of composite resin containing the AgNPs compared to the pure resin. This study has applications in printing parts using laser stereolithography.

Photoacoustic signal with two heating sources: theoretical predictions and experimental results for the open photoacoustic cell technique

A theoretical model for the photoacoustic signal with an analytical solution for the open photoacoustic cell technique is performed. The thermal diffusion (TD) and thermoelastic bending (TE) contributions from the sample and window of the open-cell are considered in the model. The analytical solution was submitted to simulations varying the thermal diffusivity, optical absorption coefficient, thickness and the amplitudes of the TD and TE contributions. The proposed theoretical model was applied to experimental data from different glasses, and quantitative analysis was achieved by calibrating the PA signal based on the TD and TE in an aluminum foil. The results demonstrate the reliability of the analytical solution for determining the thermal diffusivity of the samples.

Theoretical predictions for photoacoustic signal: Fractionary thermal diffusion with modulated light absorption source

We develop a theoretical framework, in the context of the anomalous thermal diffusion, for the photoacoustic signal. We obtain analytical predictions for the open photoacoustic cell technique by considering the thermal diffusion and thermoelastic bending effects. In these contexts, we consider different conditions for the thermal diffusivity, coefficient of optical absorption, the sample thickness and the amplitudes of thermal diffusion and thermoelastic bending contributions. Furthermore, opaque samples are also simulated as a special case of the optically transparent samples.

Experimental investigation on thermal properties of Ag nanowire nanofluids at low concentrations

New nanofluids containing Ag nanowires with different concentrations were prepared by chemical reduction method. The metallic nanowires were monodispersed and soluble in distilled water. Thermal properties of nanofluids containing Ag nanowires were obtained using photothermal techniques. The thermal-wave resonator cavity (TWRC) technique was used to obtain the samples’ thermal diffusivity. Open Photoacoustic Cell (OPC) technique was used to obtain the thermal effusivity of Ag nanowires. The thermal diffusivity and effusivity were obtained by fitting the theoretical expressions for each configuration as a function of the sample thickness and frequency to the experimental data. The thermal properties of the nanofluids seems to be strongly dependent of Ag nanowire concentration. It was observed an increase of thermal parameters when concentration of nanowires increased. Thermal conductivity behavior of the nanofluids is explained. UV–vis spectroscopy, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used to characterize the nanofluids.

Thermal study of calcium silicate material synthesized with solid wastes

This work focuses on the thermal characterization of a calcium silicate-based material synthesized with different solid wastes (chamotte and marble) for use as thermal insulation material. Thermal and structural changes occurring during heating were accompanied by differential thermal analysis, thermogravimetric analysis, dilatometric analysis, open photoacoustic cell technique, X-ray diffraction (XRD), and scanning electron microscopy. An endothermic event at 823.2 °C was interpreted as decomposition of carbonates. An exothermic event around 900 °C is associated with the crystallization of calcium silicate phases mainly wollastonite. The themophysical properties of the calcium silicate-based material (thermal diffusivity, thermal conductivity, specific thermal capacity, and thermal effusivity) are influenced by the synthesis temperature. The thermal analysis results agree well with the XRD. The calcium silicate pieces presented low thermal conductivity values (0.227−0.376 W m−1 K−1). These results suggest that the calcium silicate-based materials produced essentially with chamotte and marble wastes has high potential to be used as thermal insulation construction material.

Thermal characterization of a liquid resin for 3D printing using photothermal techniques

Thermal properties of a liquid resin were studied by thermal lens spectrometry (TLS) and open photoacoustic cell (OPC), respectively. In the case of the TLS technique, the two mismatched mode experimental configuration was used with a He–Ne laser, as a probe beam and an Argon laser was used as the excitation source. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression to the experimental data in order to obtain the thermal diffusivity (α) of the resin. On the other hand, the sample thermal effusivity (e) was obtained by using the OPC technique. In this technique, an Argon laser was used as the excitation source and was operated at 514 nm with an output power of 30 mW. From the obtained thermal diffusivity (α) and thermal effusivity (e) values, the thermal conductivity (k) and specific heat capacity per unit volume (ρc) of resin were calculated through the relationships k = e(α)1/2 and ρc = e/(α)1/2. The obtained thermal parameters were compared with the thermal parameters of the literature. To our knowledge, the thermal characterization of resin has not been reported until now. The present study has applications in laser stereo-lithography to manufacture 3D printing pieces.

Photothermal and morphological characterization of PLA/PCL polymer blends

Nowadays, some synthetic polymers have been replaced by biodegradable polymers in order to avoid environmental contamination. Among these biodegradables polymers, aliphatic polyesters such as polylactic acid (PLA) and polycaprolactone (PCL) have been widely used. In the present study, solvent-casting films of PLA, PCL and polymer blends with and without compatibilizer (PLA grafted with maleic anhydride) were prepared. The thermal diffusivity (α) of each sample was obtained by using the open photoacoustic cell technique. Morphology and thermal properties were determined by using scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry (DSC), respectively. The blends showed lower thermal diffusivity compared to pure polymers. However, when the compatibilizer was used, the highest value of thermal diffusivity was obtained. Also, cold crystallization with the highest value of enthalpy of fusion was observed for the compatibilized sample, which was revealed by DSC. To our knowledge, this is the first time that the thermal diffusivity of these biodegradable polymer blends is reported.

Annealing Effect on Photoacoustic Characterization of NiSe Metal Chalcogenide Semiconductor Using Phase Signal Analysis

Nickel selenide (NiSe) has been synthesized by solid state method and annealed at five different temperatures, ranging from 323 K to 823 K. The annealing effect on NiSe thermal and carrier transport properties were investigated by using open-cell photoacoustic technique. From analysis of its phase signal-frequency, thermal diffusivity, carrier diffusion coefficient, surface recombination velocity and recombination lifetime of the NiSe was determined. The results show that with increasing of the annealing temperature of NiSe sample, the thermal diffusivity and the carrier diffusion coefficient increased. The surface recombination velocity was decreasing as the annealing temperature of the sample increased. The increasing of annealing temperature of the sample also affected the trend of band-to-band recombination lifetime.

Detection of Hepatic Fibrosis in Ex Vivo Liver Samples Using an Open-Photoacoustic-Cell Method: Feasibility Study

Design of non-invasive and accurate novel methods for liver fibrosis diagnosis has gained growing interest. Different stages of liver fibrosis were induced in Wistar rats by intraperitoneally administering different doses of carbon tetrachloride. The liver fibrosis degree was conventionally determined by means of histological examination. An open-photoacoustic-cell (OPC) technique for the assessment of liver fibrosis was developed and is reported here. The OPC technique is based on the fact that the thermal diffusivity can be accurately measured by photoacoustics taking into consideration the photoacoustic signal amplitude versus the modulation frequency. This technique measures directly the heat generated in a sample, due to non-radiative de-excitation processes, following the absorption of light. The thermal diffusivity was measured with a home-made open-photoacoustic-cell system that was specially designed to perform the measurement from ex vivo liver samples. The human liver tissue showed a significant increase in the thermal diffusivity depending on the fibrosis stage. Specifically, liver samples from rats exhibiting hepatic fibrosis showed a significantly higher value of the thermal diffusivity than for control animals.

Effect of Silver Nanoparticles on the Thermal Properties of Sodium Acetate Trihydrate

Sodium acetate trihydrate (SAT) is used as a phase change material (PCM) because of its high latent heat of fusion. Mixtures were prepared with SAT, a blend of the polymer sodium carboxymethil cellulose (CMC) and silica gel, silver nanoparticles (AgNPs), and anhydrous sodium sulfate to form a composite-PCM (c-PCM) based on SAT; the relative proportions of CMC/silica gel in the blend and AgNP content were varied according to a central composite experimental design. The thermal properties were determined for raw SAT, CMC, \(\hbox {Na}_{2}\hbox {SO}_{4}\), and c-PCM samples. The thermal effusivity \((e_\mathrm{s})\) of samples was evaluated by the inverse photopyroelectric technique. The thermal diffusivity \((D_\mathrm{s})\) was obtained for samples by the open photoacoustic cell technique. The thermal conductivity \((k_\mathrm{s})\) was calculated from the obtained \(e_\mathrm{s}\) and \(D_\mathrm{s}\) values. To assess the thermal performance of the c-PCM compared to raw SAT, samples were studied through differential scanning calorimetry which served to determine the latent heat recovery (LHR). Properties \(e_\mathrm{s}, D_\mathrm{s}, k_\mathrm{s}\), and LHR were analyzed by response surface methodology and compared. The SAT-based c-PCM was found to be more thermally conductive than raw SAT. The best LHR with good thermal diffusivity and thermal conductivity was identified in the region of the central composite experimental design with medium–low AgNPs and higher proportions of CMC in the polymer blend.

Photoacoustic study of curing time by UV laser radiation of a photoresin with different thickness

This paper deals with the study of the cure of a resin in the presence of a UV laser radiation used as the excitation source, operated at λ=405nm, with an output power of 20mW. The open photoacoustic cell (OPC) technique was used to study the curing of the resins as a function of time. The curing characteristic time values were τ=10.43, 20.99, 30.18, 45.84, 67.59 and 89.55s for the resin thicknesses of 1000, 2000, 3000, 4000, 5000 and 6000μm, respectively. A parabolic behavior of the resin thickness, as a function of the curing characteristic time, was obtained. UV–vis spectroscopy and infrared Fourier transform spectroscopy (FTIR) techniques were employed to characterize the resin in order to study the optical absorption and the chemical bonds, respectively. Our work has applications in the manufacture of 3D printing parts for applications, among others, in medicine.

Measurement of Thermal Properties of Triticale Starch Films Using Photothermal Techniques

Nowadays, several commercially biodegradable materials have been developed with mechanical properties similar to those of conventional petrochemical-based polymers. These materials are made from renewable sources such as starch, cellulose, corn, and molasses, being very attractive for numerous applications in the plastics, food, and paper industries, among others. Starches from maize, rice, wheat, and potato are used in the food industry. However, other types of starches are not used due to their low protein content, such as triticale. In this study, starch films, processed using a single screw extruder with different compositions, were thermally and structurally characterized. The thermal diffusivity, thermal effusivity, and thermal conductivity of the biodegradable films were determined using photothermal techniques. The thermal diffusivity was measured using the open photoacoustic cell technique, and the thermal effusivity was obtained by the photopyroelectric technique in an inverse configuration. The results showed differences in thermal properties for the films. Also, the films microstructures were observed by scanning electron microscopy, transmission electron microscopy, and the crystalline structure determined by X-ray diffraction.

Effects of thermal oxidation on the effective thermal diffusivity of titanium alloys

Commercially pure titanium grades 1 (Ti), 2 (TiG2) and Ti–6Al–4V alloy grade 5 (TiG5) are used for many different types of biomaterials because of their excellent biocompatibility. Most of the biocompatibility of titanium is due to the formation of a passive thin oxide film (TiO2) in the presence of oxidant environments; it is basically found in two of its allotropic forms; rutile and anatase. The aim of this investigation was to evaluate the effect of thermal oxidation on effective thermal diffusivity measured by the open photoacoustic cell technique. Two sets of each material were prepared and submitted to heat treatment in air at 600 and 700 °C. The effective thermal diffusivity was correlated with the different oxide phases produced on the surfaces of the samples that were identified and quantified by Raman spectroscopy. It was observed that the predominant structure of TiO2, rutile or anatase, strongly influenced the effective thermal diffusivity of the samples.

Photoacoustic spectroscopy and thermal diffusivity measurement on hydrogenated amorphous carbon thin films deposited by plasma-enhanced chemical vapor deposition

In this work, the photoacoustic spectroscopy and the open photoacoustic cell method are employed in the thermo-optical characterization of hydrogenated amorphous carbon thin films. The samples were fabricated in a modified plasma-enhanced chemical vapor deposition system with varying deposition time from 2 to 30min. The optical absorption spectrum was determined for wavelengths of 300 to 2200nm. The optical transmission spectrum was also recorded from photoacoustic spectroscopy. The energy gap was determined from the optical absorption spectra. The thermal diffusivity was found using open photoacoustic cell technique. The thickness of the films was confirmed to be an important parameter for the optimization of the fabrication process and the improvement of thermo-optical performances of the thin films. Spectroscopic results showed lower absorption and UV transparency for the thinner film. In the infrared region the −OH band decreased with increasing film thickness. On the other hand, the thermal diffusivity measurement presented an increase of this variable with decreasing film thickness.

Open Photoacoustic Cell Configuration Applied to the Thermal Characterization of Liquid CdS Nanocomposites

CdS nanofluids were prepared by the gamma-radiation method at different radiation doses. The samples were characterized by UV–Vis spectroscopy and transmission electron microscopy. The open cell photoacoustic technique was used to measure the thermal effusivity of the CdS nanocomposites. In this technique a He–Ne laser was used as the excitation source and was operated at 632.8 nm with an output power of 70 mW. The precision and accuracy of this technique were initially established by measuring the thermal effusivity of distilled water and ethylene glycol. The thermal-effusivity values of these two samples were found to be close to the values reported in the literature. The thermal effusivity of CdS nanofluids decreased from (0.453 to 0.268) \(\mathrm {W}\cdot \mathrm {S}^{1/2}\cdot \mathrm {cm}^{-2}\cdot \mathrm {K}^{-1}\) with increased dosage of gamma radiation.

In vitro thermal diffusivity measurements as aging process study in human tooth hard tissues

In the present work, the Open Photoacoustic Cell Technique was used to find effective thermal diffusivity of human tooth hard tissues, a thermal variable of great interest in the biological science, and inorganic materials. The aging process of the tooth enamel and dentin was analyzed through its effective thermal diffusivity. The study in vitro of these samples showed an increase and posterior decrease with aging of the samples. The values found for the enamel and dentin samples, varied from (36−55)×10−4 cm2 s−1 and (20−32)×10−4 cm2 s−1, respectively.

The thermoelastic bending and thermal diffusion processes influence on photoacoustic signal generation using open photoacoustic cell technique

Thermal diffusion and thermoelastic bending are two consequences of heating generated on the sample surface. Both are employed in Open Photoacoustic Cell (OPC) technique to measure the thermal diffusivity of the sample. In this work, we explore the potential use of the OPC technique to study the effectiveness of thermoelastic bending process and thermal diffusion process on photoacoustic signal (S) generation in solids. More specifically, it is observed that if the thermoelastic bending process becomes more effective while the sample thickness is decreased, this information can be used to obtain a method to self-check the value of the thermal diffusivity parameter measured. The method is based on the measurement of the thermoelastic bending parameter as a function of the sample thickness (ls). The expected dependence of the thermoelastic bending parameter (C2) with the sample thickness, according to the theoretical model, is C2 ∝ ls−3. Our results for aluminum metallic samples give a C2 ∝ ls−2.8 dependence. Also, a thermal diffusivity value of αexp = (8.4 ± 0.3) × 10−5 m2/s was measured for metallic aluminum. This value is in good agreement when compared with the theoretical value αAl = 8.6 × 10−5 m2/s.