Thermal Lens (TL) and spectroscopic characterizations were performed in CdSe/ZnS core-shell quantum dots (QDs)
embedded into two commercial dental resin composites. The thermal-optical studies were performed in CdSe/ZnS QDs
(core size Φ= 4.1 nm) and PMMA-encapsulated CdSe/ZnS (Φ= 3.7 nm) embedded in restorative dental resins at
concentration of 0.025 and 0.42 % in mass, respectively. The thermal diffusivity (D) results are characteristics of the
dental resin composites studied. Photoacoustic (PA) technique results for the dental resin composites support the TL
In the photoacoustic technique, the signal is proportional to the heat produced in a sample as a consequence of modulated light absorption. This technique allows the spectroscopic characterization of multilayer systems: as the thermal diffusion length varies with the light modulation frequency, one can obtain the depth profile of the sample by analyzing the frequency-dependence of the signal. As the photoacoustic signal depends on thermal and optical properties of the sample, structural changes in the system under analysis account for signal variations in time. In this work, photoacoustic spectroscopy was used to characterize samples of sunscreen and the system formed by sunscreen plus skin. We used photoacoustic spectroscopy to monitor the absorption kinetics of sunscreen applied to samples of human skin, characterizing alterations in the human skin after application of sunscreen. Measurements used 250W Xe arc lamp as light source, for wavelengths between 240nm and 400nm. This range corresponds to most of the UV radiation that reaches Earth. Skin samples were about 0,5cm diameter. The absorption spectra of sunscreen was obtained. Finally, photoacoustics was employed to monitor the absorption kinetics of the sunscreen applied to skin samples. This was done by applying sunscreen in a skin sample and recording the photoacoustic spectra in regular time intervals, up to 90 minutes after application. According to measurements, light absorption by the system sunscreen plus skin stabilizes between 25 and 45 minutes after sunscreen application. Results show that this technique can be utilized to monitor drug delivery and farmacokinetics in skin samples.
The photoacoustic technique is based on the absorption of modulated light by a sample and subsequent heat generation. This generates thermal waves that propagate in the surrounding media. According to the Rosencwaig-Gersho Model, such waves produce the pressure oscillation detected as the photoacoustic signal. This technique allows the spectroscopic characterization of multilayer systems: as the thermal diffusion length varies with the modulation frequency of the absorbed light, the depth profile of a sample can be studied by the analysis of the photoacoustic signal at different modulation frequencies. In this work, photoacoustic spectroscopy was used to characterize different human skin samples. Measurements were performed at 70Hz and 17Hz, using a 1000W Xe arc lamp as the light source, for wavelengths between 240nm and 700nm. Skin samples were about 0,5cm diameter. It was possible to obtain the photoacoustic absorption spectra of the stratum corneum and of a deeper layer of epidermis; when the lower modulation frequency is utilized, photoacoustic spectroscopy characterizes the absorption of the whole epidermis, because in this case the thermal diffusion length is thicker than that of the stratum corneum. Photoacoustic spectroscopy was also employed to monitor the drying kinetics of the skin. This was done by analyzing the time evolution of the photoacoustic spectra of skin samples. Pre-treatment of the samples included different periods in a drying chamber. Measurements show that the photoacoustic spectra changes according to the humidity of the skin. Future work includes detailed monitoring of skin hydration.
The aim of this work was to characterize the degree of photoactivation of the Z250 resin through photoacoustics. In this technique, the signal detected is proportional to the heat produced in a sample as a consequence of light absorption. This technique has been used for more than 20 years as a work tool in diverse fields of biological and biomedical sciences. Through photoacoustic measurements, it is possible to study optical and thermal properties of samples, and to obtain information on the characteristic times involved in photoinduced processes, as the photoactivation of composed resins. After application on the surface, the Z250 resin is photoactivated by incidence of continuous light (λ = 475 ± 15 nm) coming from a photodiode. This leads to the polymerization of the resin, modifying its thermal properties. The experimental method employed in this work was the following: a) the resin was applied on an aluminum sheet placed in contact with the photoacoustic cell (front incidence); b) modulated white light was applied in the lower surface of the aluminum sheet, black-painted to increase the light absorption; c) the photothermal signal was observed. Polymerization was evaluated through the alteration of the photoacoustic signal caused by the activation of the resin promoted by the incidence of the continuous light, for different activation times. The results show that the polymerization of the resin substantially modifies the photoacoustic signal, indicating that the degree of photoactivation can be evaluated through photoacoustic measurements.
In this work is presented the use of Photoacoustic as an alternative technique to monitor the curing process of odontological materials, emphasizing the resins chemically activated (RCA). Through photoacoustic measurements, it is possible to study optical and thermal properties of samples, and to obtain information on the characteristic times involved in the curing processes. For this study the samples were analyzed to evaluate the polymerization of the RCA for different temperature. The results obtained show the viability of applying the Photoacoustic Techinques to monitor the polyermization kinetic of odontological resins, allowing for a qualitative and quantitative interpretation.