Modifications of the optical and vibrational properties in polylactic acid films by the addition of gold nanoparticles produced by laser ablation in chloroform

Gold nanoparticles (AuNPs) have been produced by laser ablation in chloroform and then embedded in polylactic acid (PLA) thus realizing PLA/Au nanocomposite films. Two initial volumes of chloroform of about 5 and 4 mL have been used, thus obtaining two different PLA/Au nanocomposite films. The effects of the embedded AuNPs into PLA films have been studied using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and ultraviolet/visible (UV-Vis) absorption spectroscopy. In the ATR-FTIR spectra, as AuNPs are embedded in PLA and their concentration grows up, the PLA characteristic vibrational features maintain their positions in wavenumber, but their IR absorption increases. This result confirms the presence of AuNPs in PLA and suggests that no strong chemical interaction occurs between PLA and AuNPs and no new bonds are formed. Concerning the UV-Vis optical properties an increase in the PLA optical absorption in the visible region has been also observed when AuNPs are embedded. The AuNPs presence is attested by the appearance of localized surface plasmon resonance (LSPR) absorption peak between 500 and 600 nm that shifts at longer wavelengths and broadens as the AuNPs concentration increases. The PLA absorption edge has been determined and its position in wavelength increases with increasing AuNPs concentrations. This observed absorption edge red shift indicates a decrease in the PLA band gap probably due to the electronic levels introduced by the embedded gold nanoparticles.