Caracterização óptica e morfológica de filmes automontados de POMA/PPV

Abstract

This work presents the optical and morphological characterization of layer-by-layer (LBL) ultra-thin films from poly(p-phenylene vinylene) (PPV) and poly(o-methoxyaniline) (POMA). The PPV films were processed using the precursor polymer poly(xylylidene tetrahydrothiophenium chloride) (PTHT) and the sodium dodecylbenzenesulfonate (DBS). The films were deposited on glass substrate (BK7) with 2, 5, and 10 layers of POMA in esmeraldine salt form and 5, 10, 25 and 50 layers of PTHT+DBS. The PPV+DBS films on POMA layer were obtained from the thermal conversion process at 110oC and 230 oC under vacuum (10-2 atm) environment during 2 h. The optical characterizations were performed with absorbance, photoluminescence as function of the sample temperature, selective excitation, polarized absorbance and photoluminescence. The Raman spectroscopy and Atomic Force Microscopy (AFM) characterization were performed to study the structural and surface morphological properties, respectively, of LbL POMA/PPV films. The absorption experiment shows that the PPV+DBS layers are adsorbed in same ratio, independently, on the number of POMA layers and the thermal conversion temperature. The line shape of the photoluminescence (PL) is not affected with the PPV conversion reaction for all samples on POMA layer. High thermal stability of PPV was observed; witch the integrated PL decreasing only 10% when the temperature was increased from 10 to 300K. On the other hand, the PL spectra for LbL with 25 layers of PPV+DBS deposited on glass substrate decrease 80% in the same sample temperature range. The line shape of selective excitation spectra is similar of the absorbance one for LBL POMA/PPV films. The molecular order analyses through of the polarized absorbance and PL show that the POMA and PPV molecules are, preferential, oriented in the dip direction. This result was confirmed via AFM analysis. From Raman data, it was possible to identify the polymer/polymer interface region and the molecular group s interaction between POMA and PPV. Finally, a physical model was proposal based on experimental data to explain the optical properties of PPV on POMA layer.