Efeitos da adição de pontos quânticos de carbono sobre as propriedades termo-ópticas de polímeros

Abstract

Polymers are materials with specification ability, which has led to wide use in several areas. Due to the well-established understanding of obtaining polymers, the discovery of new applications now takes place through chemical and physical modification of existing polymers, rather than the development of new syntheses. One way is by doping polymer matrices with carbon quantum dots, which are carbon nanoparticles with unique lumi#nescent properties. The Z-scan technique is a method of measuring third order nonlinear optical phenomena of materials, from which it is possible to obtain thermo-optical pro#perties parameters about the material. In particular, when used with thermal lens model, information on the nonlinear refractive index and thermal diffusivity is obtained. In this work, we investigated the effects of the addition of methyl red carbon quantum dots (CDMR) in polyvinyl alcohol (PVA) polymeric films, to their thermo-optical properties, using the time-resolved Z-scan technique. The carbon dots synthesis was made using the methyl red azo dye as precursor in the hydrothermal method, in a microprocessed oven at 200◦C for a 10 hours period. The polymeric films were made from a 10% PVA solution doped with 1.0% and 2.5% of CDMR deposited on a smooth surface until it was dried (48h). The thickness of the films were in the range of 110−182 µm. Through the absorp#tion spectrum, we observed that the PVA film with the addition of carbon quantum dots derived from methyl red presents the typical bands for the carbon quantum dots corres#ponding to the transitions of the electronic levels of the nucleus and the surface. Using the Z-scan technique, for films with 1.0% we found that the induced phase shift θ has a value θ = 0.034 ± 0.001, and the thermal diffusivity has a value D = 1.20 × 10−3 cm2/s. For 2.5% films we got θ = 0.066 ± 0.002 and D = 1.35 × 10−3 cm2/s. Then, the increase in the concentration of the carbon dots in the polymer matrix resulted in an increase in the amplitude of the Z-scan curve, an increase in the parameter θ and in the thermal diffusivity of the films. Therefore, we obtained that the confinement of the nanoparticles synthesized from methyl red in the films does not change the spectroscopic properties of the nanoparticles significantly. As we have also seen, from the Z-scan technique, the increase in concentration in the films significantly modifies the thermo-optical properties of the polymeric films.