Síntese de nanopartículas de ouro e prata em matriz polimérica sobre substratos modificados por litografia de nanoimpressão

Abstract

This work presents the study of synthesis, organization, and characterization of silver nanoparticles (AgNPs) in modified substrates by microcontact-printing (μCP) using the copolymer polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP). The deposition of gold nanoparticles (AuNPs) over PS-b-P2VP films was also investigated. The SERRS activity of these systems were tested with two dye molecules, IR-820 and Blue of Nile. The nanocomposite thin films were characterized by electronic UV-VIS spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Prepatterned chemically heterogeneous glass substrates were prepared by μCP, to which octadecyltrichlorosilane (OTS) solution was selectively transferred using a PDMS stamp with periodic microscale stripes that were obtained from a CD, creating regions with different hydrophilicity. These OTS-patterned substrates have the purpose of directing the assembly of the domains of the PS-b-P2VP. AFM was used for the characterization of these substrates. PS-b-P2VP, with different compositional ratios of PS to P2VP, was used for the in situ synthesis of AgNPs on prepatterned substrates (which were prepared using μCP). The AFM images of the AgNP/PS-b-P2VP films reveal the importance of the modification of the substrate, the molecular weight of the copolymer, and heating, in the assembly, morphology and optical properties of the films. It was observed that multifaceted nanoparticles dispersed well in the films spin-coated onto the prepatterned substrates when compared with the films spin-coated in bare glass substrates. The UV-VIS absorption spectra show that the stop band is only detected in the films spin-coated onto the prepatterned substrates, because of the microphases organization of the PS-b-P2VP. AuNPs were synthetized and then deposited onto the PS-b-P2VP films with different treatments. The following treatments were applied: immersion of the film in ethanol or water for 10 min, and thermal treatment. To verify the importance of the treatment in the adsorption and optical properties of the AuNPs, synthetized films without any prior treatment were also used. When comparing the prepared films, it was noticed that the ethanol treatment induced a more homogeneous adsorption of the AuNPs onto the glass substrate and that the thermal treatment created a PS-b-P2VP film with gyroid morphology, where the AuNPs were deposited preferentially in the P2VP microdomains.