Open Photoacoustic Cell Research Articles

Photoacoustic evaluation of molecular weight and crosslinking effects on thermal diffusivity in Poly(N-vinyl-2-pirrolidone)

The thermal diffusivity of Poly(N-vinyl-2-pirrolidone) (PVP) samples was investigated using open photoacoustic cell technique (OPC) as function of molecular weight and crosslinking. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X ray diffraction (XRD) techniques were also used to the PVP characterization.

Open Photoacoustic Cell study of thermal diffusivity of Nafion® as a function of water content

The Dupont Nafion® (acid polymer perfluorsulfonic/PTFE copolymer in an acid form H + ) is derived from Teflon® (PTFE) and both present great similarities. In order to study thermal properties of the Nafion®, we used theopen photoacoustic cell (OPC) to measure the longitudinal α⊥ and the thermal lens technique (TLS) for the planar direction, α H . From OPC experiment it was found an averaged (Nafion® in nature) value α⊥ = (6.5 ′ 0.4) x 10 - 4 cm 2 /s whilst TLS gave α H = (7.0 ′ 0.2) x 10 - 4 cm 2 /s. The value found, α⊥ ∼ α H , means that there is no significant anisotropy in the Nafion® foil. Water content dependence of thermal diffusivity for ten samples dipped in water showed a minimum near 4 h (∼ 4.5 x 10 - 4 cm 2 /s) and goes to a saturating value after 28 h (∼ 5.5 x 10 - 4 ). On the other hand, in experiment where the sample is left to dry in the ambient air, α⊥ present a transitional behavior near 5 h off water (∼ 6.0 x 10 - 4 ) and diminish monotonically after 28 h. It is believed that thermal diffusivity can be related with water content and it may be helpful in the understanding of permeation in the Nafion® membrane.

Photothermal methods and atomic force microscopy images applied to the study of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) dense membranes

AbstractThermal and transport properties of some polyhydroxyalkanoates (PHAs), poly‐3‐hydroxybutyrate and poly‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate copolymers at different concentrations (8, 14, and 22%), were studied by using photoacoustic and photothermal techniques. Mass diffusion coefficients were obtained for carbon dioxide and oxygen by using a gas analyzer. Specific heat capacity measurements were performed by monitoring temperature of the samples under white light illumination against time. Thermal diffusivities were determined by using the open photoacoustic cell configuration. The results were discussed considering the incorporation of hydroxyvalerate units in the poly(3‐hydroxybutyrate) unit cell and were correlated with atomic force microscopy images of the upper surface of membranes. New information on transport properties of PHAs is provided. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1491–1497, 2005

On the thermal characterization of a HPHT sintered WC–15% wt Co hardmetal alloy

Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders, compacting, and liquid phase sintering. A new method to process hardmetal parts is hereby described. Parts of WC–15% wt Co were processed by using high pressure high temperature sintering (HPHT). The pressure of 5 GPa, temperature of 1350 °C, and time of 2 min of sintering was used. Results are shown as a function of micro-structure, densification, and hardness measurements. The open photoacoustic cell technique (OPC) was carried out in order to measure the thermal diffusivity of the hardmetal. In addition, heat capacity was considered and the thermal conductivity calculated. Results matched with the values of the literature where other photoacoustic techniques have been employed.

Open Photoacoustic Cell Technique as a Tool for Thermal and Thermo-Mechanical Characterization of Teeth and Their Restorative Materials

The thermal diffusivity and thermal expansion coefficient of teeth and three of their most common restorative materials (Amalgam Phase Alloy, Ionomer Fuji II LC, and Resin 3MFPITEK Lutine TMZ250) were studied by means of the open photoacoustic technique. These results were then used as a basis for the theoretical simulation of the photothermal process taking place as a consequence of modulated illumination of a two-layer system formed by the tooth and the restorative material. The model accounts for the coupling of thermal waves and thermoelastic vibration in the two-layer system.

Thermal characterization and determination of recombination parameters in CdTe films on glass substrates by using open photoacoustic cell technique

CdTe is a semiconductor with a wide variety of applications and perspectives for electronic industry (high-efficiency photoelectric cells, infrared radiation detectors, etc.). In the present work, we used photoacoustic (PA) technique to study the thermal properties and the surface recombination velocity in CdTe/glass samples. Experimental PA phase signal as a function of modulation frequency in a heat transmission configuration was fitted to the theoretical expression for PA signal, which takes into account the heat sources resulting from the absorption of light in semiconductors and the nonradiative processes involved, which depend on their thermal, optical and electronic transport properties. By this procedure, it was possible to determine the thermal diffusivity and the surface recombination velocity in these samples. The studied samples were thin polycrystalline CdTe film deposited on glass slides. CdTe layers were deposited by a hot-wall closed-spaced vapor transport method, known as gradient recrystallization and growth. The values for the deposition parameters used in this study were the following: 700°C for the source temperature and 450 and 550°C for the substrate temperatures with three different deposition times from 5 to 20 min (then three different film thicknesses were obtained). A clear increment in the surface velocity and surface roughness is observed as the film thickness is increased.

Heat diffusion and thermolastic vibration influence on the signal of an open photoacoustic cell for two layer systems

Thermal diffusion and thermoelastic vibration in two layer systems is studied using photoacoustic spectroscopy. Three different two layer systems, copper/lead–tin (Cu/Pb–Sn), aluminum/paint (Al/paint) and aluminum/polyvinyl-chloride (Al/PVC) are studied. A model is developed considering that both layers present thermoelastic vibration and heat diffusion. It is shown that our equations can be used to obtain the theoretical photoacoustic signal independent of the mechanical properties when the thermal and thermomechanical properties of the composing layers are similar. It is shown that this approximation is much better suited for the study of metal/metal systems where the coupling of the thermoelastic bending is smooth. The restrictions of this approach and the possible extensions to study systems with different thermal expansion and mechanical behavior are discussed.

Photoacoustic investigations on thermal diffusivity of CuGa1–xFexO2

The thermal diffusivity of CuGa1–xFexO2 solid solutions with x = 0, 0.1, 0.2 and 1 has been investigated using an open photoacoustic cell (OPC). The thermal diffusivity of the samples is evaluated from the phase data associated with the photoacoustic signal as a function of modulation frequency in transmission detection configuration (TDC). Analysis is based on the theory developed by Rosencwaig and Gersho. The effect of thermoelastic bending on thick samples is studied. The results are confirmed by performing measurements on samples of different thicknesses.

Determination of thermal effusivity of liquids by use of open photoacoustic cell and front excitation configuration

The applied procedure of thermal effusivity determination for liquid samples taking advantage of photoacoustic signal amplitude measurement with microphone registration is presented. The experimental results obtained for distilled water and ethyl alcohol are shown to illustrate the sensitivity of the applied procedure. The results are in reasonable agreement with the data obtained from the literature.

Thermal characterization of intrinsic and extrinsic InP using photoacoustic technique

An open photoacoustic cell operating in the low range of chopping frequency has been employed to evaluate the thermal diffusivity values of intrinsic InP and InP doped with S, Sn and Fe. The experimental set-up is calibrated by the evaluation of thermal diffusivity value of pure Si and GaAs. The present investigation shows that doped samples show a reduced value for thermal diffusivity compared to intrinsic sample. From the analysis of data it is also seen that nature of dopant clearly influences the thermal diffusivity value of semiconductors. The results are explained in terms of phonon assisted heat transfer mechanism in semiconductors.

Photoacoustic determination of iron in corn meal.

We report here on the use of the photoacoustic technique for the determination of low concentrations of total iron in corn meal samples. The determination of this element in food is of considerable interest because several foods are currently enriched with it at proper levels in order to increase the resistance of people, after consumation, to several diseases, such as anemia. The proposed technique is based on an open photoacoustic cell configuration in conjunction with a suitable colorimetric method. We applied it to a measurement of the total iron concentration in corn meal samples. The results agree very well with those obtained using a conventional spectrophotometric method, showing the possibilities of new experimental methodologies based on photothermal methods to perform this kind of study, with the advantage of a higher sensitivity and increment of the range of appreciable absorbance.

Photoacoustic measurements of thermal diffusivity of amylose, amylopectin and starch

The thermal diffusivity and thermal conductivity of amylose, amylopectin and starch were measured at room temperature and low moisture content using the open photoacoustic cell detection technique. These thermal parameters are an important heat transport property of foods, which are useful in computations, simulations and control of several unsteady-state foods processing operations. The thermal conductivity of these polymers is predicted from the heat diffusion theory and the ratio of the photoacoustic amplitude of the sample and other material of known thermal parameters. The thermal parameters of those granular foods obtained using the photoacoustic spectroscopy are compared with those reported in previous works.

Photorespiration and temperature dependence of oxygen evolution in tomato plants monitored by open photoacoustic cell technique

The open photoacoustic cell was used to monitor the evolution rate of oxygen from tomato leaves. Estimates of the relative amount of released oxygen in vivo and in situ conditions as influenced by ambient temperature are being presented. Photorespiration phenomenon is shown to dominate above a critical temperature. The evolution of this critical point is analyzed as a function of the environmental temperature.

Microstructure effects on the thermal properties of vacuum sintered AISI 316L stainless steel

The photothermal technique open photoacoustic cell and the non-Adiabatic thermal relaxation calorimetric are applied to measure thermal properties of the sintered stainless steel AISI 316L as a function of the porosity. The results showed that thermal diffusivity and thermal conductivity values as a function of the applied uniaxial pressure presented a strong correlation with the surface area of contact of the particles, which constitute the porous medium. Besides, the study of the relationship between physical properties, such as mass density, porosity, and permeability and the microstructure shows that the greater the particle interaction the better the thermal properties correlation.

Thermaldiffusivity of liquid crystalline polymers measured using opencell photoacoustic technique

Thermal diffusivity of two side-chain liquidcrystalline polymers is reported in this paper. An openphotoacoustic cell in the heat transmission configuration isemployed for the measurements. The investigation shows that thethermal transport properties of these materials are mainlydetermined by their molecular structure.

On the application of the photoacoustic methods for the determination of thermo-optical properties of polymers

In this paper, the application of photoacoustic methods to study thermo-optical and spectroscopic properties of polymers is described. The Photoacoustic Spectroscopy, the Two-Beam Phase-Lag and also the so-called Open Photoacoustic Cell methods will be presented. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations of the methods as compared with conventional measurements. Applications for spectroscopic and depth profile analysis and also for thermal properties measurements in several polymers samples are discussed.

Determination of total polyphenolic content in red wines by means of the combined He-Ne laser optothermal window and Folin-Ciocalteu colorimetry assay.

The He-Ne laser (632.8 nm) and the concept of optothermal window (OW), a variant of the open photoacoustic cell, were combined with the Folin-Ciocalteu colorimetry assay to quantitate phenolics in four red wines. The total polyphenolic content in selected red wines varied between 786 and 1630 mg/L gallic acid equivalent (GAE) as determined by OW-Folin-Ciocalteu colorimetry, which compares well to 778 and 1614 mg/L GAE obtained for the same wines by means of classical spectrophotometry. The originality and merit of OW colorimetry used here is that, unlike what is encountered in conventional spectrometry, no intermediate dilution step is required when total polyhenolics are determined in red wine. The precision, defined as the closeness to each other of 256 replicate readings of the OW signal, is generally better than 2%.

Thermal diffusivity measurement of Zn, Ba, V, Y and Sn doped Bi-Pb-Sr-Ca-Cu-O ceramics superconductors by photoacoustic technique

The simple open photoacoustic cell technique is demonstrated for measuring the thermal diffusivity of the Zn, Ba, V, Y and Sn doped Bi-Pb-Sr-Ca-Cu-O superconducting ceramic samples. It is based upon the measurement of the photoacoustic signal as a function of the modulation frequency in the region where the sample thickness, ls, equal to the thermal diffusion length of the sample, μs. The obtained thermal diffusivity values of Ba, V, Y and Sn doped in Bi-Pb-Sr-Ca-Cu-O system increase with the increasing dopant concentration at Ca side. However, the thermal diffusivity values of Zn doped sample decrease with the increasing of dopant concentration in the system. The measured thermal diffusivity value was found to be very dependent on the dopant atom and dopant concentration.

Self-normalized photoacoustic thermal diffusivity measurements of dental resins

A new self-normalized photoacoustic technique, using the Open Photoacoustic Cell configuration, to carry out measurements of thermal diffusivity of materials is presented. This new methodology involves a linear fitting procedure of the photoacoustic amplitude signal. To carry out the analysis one requires the ratio of signal amplitudes from two samples of the same material and of different thicknesses. This rationing procedure leads to the elimination of the usual requirement for instrumental transfer-function normalization. The thermal diffusivity for three dental resins is measured with this simple methodology and very good agreement is found with values for similar materials reported by means of more complicated techniques.

Photoacoustic studies on <bold>n</bold>-type InP

We discuss an open photoacoustic cell study on sulfer-doped n-type InP wafer. The thermal diffusivity of the sample is evaluated from the phase data associated with the photoacoustic signal as a function of the modulation frequency under heat transmission configuration. Analy- sis is made on the basis of the Rosencwaig-Gersho theory and the re- sults are compared with those from earlier reported photoacoustic stud- ies of semiconductors. Our investigation clearly indicates that the instantaneous thermalization process is the major heat diffusion mecha- nism responsible for the photoacoustic signal generation in an InP sample. © 2002 Society of Photo-Optical Instrumentation Engineers.