Investigation of film forming, optical and electrical properties of AgNPs doped PS/AgNPs composites

In this study, film formation behavior of pyrene (P) labeled polystyrene (PS) based and silver nanoparticles (AgNPs) doped composite films were investigated by using two different film formation methods such as thermal annealing and exposuring to solvent vapor. In order to understand the effects of mass fraction of AgNPs on film formation, nine different powder films were prepared by using drop casting method and each film contains different amount of AgNPs in the range of 0-50 wt%. All powder films were prepared at the room temperature. In the first experiment, all of powder films were annealed at various temperatures between 100 °C and 250 °C with 10 °C temperature increment separately. After each annealing step, steady state fluorescence (SSF) technique, fast transient fluorescence (FTRF) technique and photon transmission (UVV) technique were used in order to monitor film formation process. The classical latex film formation is observed in the range of 0-30 wt% of AgNPs content. In this range, film transparencies are found between 40-85%. Above this range, instead of continous films, partially film formation is seen and transparency of films decreased drastically with increasing AgNPs content. Fluorescence enhancement and reduced lifetime were also observed with increasing AgNPs content in the range of 3-20 wt% due to the to interactions between the pyrenes and the electron plasma in nearby silver nanoparticles. Scanning electron microscobe (SEM) images were also taken to compare optical data with film morphology. The SEM results is shown as compatible with the optical observations. Electrical conductivity of the films were also measured by using two probe method which is used to measure surface resistivities (Rs) of the films. The surface resistivity was converted into surface conductivity () using the relation (S)=1/Rs (). It is seen that incereasing AgNPs content did not alter so much the conductivities of the films. All films were determined as dielectric materials. In the second experiment, seven different powder films including 0, 1, 5, 10, 20, 30, 50 wt% of AgNPs content were used in order to obtain continous films by using chemical vapor deposition method. The film formation process were monitored by using FTRF and UVV techniques. It is seen that solvent vapor acts as a fluorescence quencher and successfully induce the latex film formation process. In the range of 0-20 wt% of AgNPs content, films were found transparent (above 85% transparency). Above this range, translucent films were obtained. It is observed that lifetime of P also decreased with increasing vapor exposure time. Thus, the quenching effect of organic solvent is verified due to FTRF data. Also reptation frequencies from UVV and FTRF data were calculated by using de Gennes' reptation model. For both techniques, reptation frequencies first decrease up to 10 wt% of AgNPS, then starts to increase. In order to support our optical data, a comparison were made between these results and the SEM images of the films. It is shown that the solvent vapor not only affects the film formation of the films, but also controls the morphology of the films. Above 10 wt% of AgNPs content, aggregations are seen on the film morphology. So that, istead of continous film, partially film formation is observed above this ratio. This results were found consistent with the optical data according to behavior of reptation frequencies. Electrical conductivity of the films were also measured. Altough the conductivity of composites were showed an increase of 3 orders of magnitude with increasing AgNPs content, the obtained films were found still as dielectric materials. To sum up, the properties of composite films were compared according to their film formation methods. As it is clearly seen from experimental results, vapor exposured films were found more transparent then annealed films. Altough the electrical conductivity of vapor exposured films were higher, all films were found as dielectric materials. According to SEM images, classical latex formation process is occured for both experiments. The findings of first experiment potentially provide a new approach for studying the film formation process of metal doped polymer composites. In this respect, this work presents a simple and efficient method for modulating the emission intensities of luminescent plastics and for the next generation of smart fluorescent polymers. Second experiment also supported the effects of AgNPs on transparency, conductivity and morphology of the films. Both methods are cheap and easy to apply. It can be said that, these methods are also appropriate for industrial applications.