Langmuir and Langmuir–Schaefer Films of Poly(3-hexylthiophene) with Gold Nanoparticles and Gold Nanoparticles Capped with 1-Octadecanethiol

Abstract

This paper reports on the production of Langmuir films of regioregular poly(3-hexylthiophene) (P3HT) and their characterization by surface pressure isotherms and UV–vis in situ spectroscopy aiming at the best spreading conditions. Hybrid films containing the polymer and gold nanoparticles were obtained through the use of the optimized parameters for neat P3HT. Two types of hybrid films with P3HT and gold nanoparticles were studied. In the first type, gold nanoparticles in an aqueous solution were used in a subphase of a Langmuir trough and the polymer spread on the air/water interface. In the second type, 1-octadecanethiol capped gold nanoparticles (AuNpOctathiol) were used in a mixture with P3HT in chloroform and spread on the air–water interface. The Langmuir films were transferred to several solid substrates by the Langmuir–Schaefer (LS) method. The surface morphology was characterized by Scanning Electron Microscopy with Field Emission Guns (SEM-FEG), and the presence of gold nanoparticles in the films was confirmed. The growth of the layers in the films was monitored by transmission UV–vis spectroscopy, and the existence of optical anisotropy was investigated by polarized UV–vis spectroscopy. The results imply that the polymer backbone adopts a preferential orientation during the compression, which has a strong component parallel to the trough barrier, and is influenced by the presence of the nanoparticles in the films. The photostability of the films was studied by their exposition to a white light, and the hybrid films formed with P3HT and AuNpOctathiol showed an increase in the photostability, in comparison to the neat P3HT. Such an increase indicates that somehow the AuNpOctathiol molecules provide some protection against the photodegradation of P3HT.