CONICET | Buscador de Institutos y Recursos Humanos

Noble metal nanoparticles (NPs) can efficiently release heat under irradiation by conversion of electromagnetic energy into thermal energy. The electromagnetic field drives mobile carriers inside the NPs and the energy gained by these carriers is turned into heat. Heat generation becomes particularly strong in the regime of plasmon resonance. Methacrylate monomers cured at room-temperature contain unreacted monomer because the polymerization reaction is stopped by vitrification. The conversion of C=C is commonly increased by heating the polymer at ~ 20 °C above the glass transition temperature. Silver nanoparticles (AgNPs) can act as efficient sources of heat, so, the partially cured polymer can be postcured by means of irradiation with light of proper wavelength; i.e., in the absence of external heating. The plasmonic heating effect of AgNPs was studied by irradiating nanocomposites based on AgNPs-methacrylate monomer. AgNPs were in-situ synthesized in methacrylate monomers by chemical reduction of silver nitrate with hydroquinone methylether. The methacrylate monomer was 2,2-bis[4-(2-methacryloxy ethoxy) phenyl]propane (BisEMA, Esstech, Essington, PA). The resulting AgNPs/BisEMA suspensions containing 50, 100 and 150 ppm AgNPs were photopolymerized with a 365-nm LED. The conversion of C=C was measured by FTIR. UV-vis spectra (1601 PC, Shimadzu spectrometer) of AgNPs/BisEMA suspensions showed plasmon resonance absorption bands centred at 410 nm. The temperature of samples during irradiation with a LED with irradiance overlapping the plasmon resonance absorption band of the AgNPs was monitored with fine K-type thermocouples. The temperature of 1-mm thick specimens irradiated during 16 or 40 s increased 20 and 30 °C respectively. The increase in conversion was not large (~10%) probably due to the short irradiation time. Studies with a LED unit that enables longer irradiation times are being carried out.