A study on film formation and fluorescence enhancement of PS latex/AgNPs composites depending on AgNPs content and annealing

In the work reported here, we investigated the characteristic change in film formation, optical, morphological and electrical properties of pyrene (P) labeled polystyrene (PS) latex/silver nanoparticles (AgNPs) (PS/AgNPs) composites by using steady state (SSF) and fast transient (FTRF) fluorescence techniques in conjunction with UV–VIS (UVV) technique. Nine different mixtures were prepared by mixing of PS latex dispersion with different amount of AgNPs in the range of 0–50 wt%. PS/AgNPs films were then prepared on glass substrates using drop casting method and drying at room temperature. After drying, film samples were separately annealed above the glass transition temperature (Tg) of PS ranging from 100 to 280 °C. Fluorescence emission spectrum, fluorescence decay curve and transmittance of these composites were measured after each annealing step as a function of AgNPs content. The emission spectrum became narrower with increasing AgNPs content due to interactions between the pyrenes and the electron plasma in nearby silver nanoparticles. Fluorescence enhancement and reduced lifetime were also observed with increasing AgNPs content in the range of 3–20 wt%. Almost a 4 fold increase in emission intensity of pyrene were observed for 10 wt% of AgNPs content film. In order to monitor the film formation process, fluorescence intensities (IP) from P and transmitted light intensity (Itr) through the films were measured after each annealing step. Below 40 wt% of AgNPs, two distinct film formation stages, which are named as void closure and interdiffusion processes, were seen in fluorescence data. However, above 40 wt%, no change was observed in IP upon annealing, whereas transparency decreased overall with increasing AgNPs content. The electrical conductivity of these composites showed very little increase with increasing AgNPs. Film morphologies were also found as consistent with optical data.