Thermal Annealing of Polymer Nanocomposites via Photothermal Heating: Effects on Crystallinity and Spherulite Morphology

Metal nanoparticles embedded within polymeric systems can act as localized heat sources, facilitating in situ polymer processing. When irradiated with light resonant with the nanoparticle's surface plasmon resonance (SPR), a nonequilibrium electron distribution is generated which rapidly transfers energy into the surrounding medium, resulting in a temperature increase in the immediate region around the particle. This work compares the utility of such photothermal heating versus traditional heating in gold nanoparticle/poly(ethylene oxide) nanocomposite films, crystallized from solution and the melt, which are annealed at average sample temperatures above the glass transition and below the melting point. For all temperatures, photothermally annealed samples reached maximum crystallinity and maximum spherulite size faster. Percentage crystallinity change under conventional annealing was analyzed using time-temperature superposition (TTS). Comparison of the TTS data with results from photothermal experiments enabled determination of an effective dynamic temperature achieved under photothermal heating which is significantly higher than the average sample temperature. Thus, the heterogeneous temperature distribution created when annealing with the plasmon-mediated photothermal effect represents a unique tool to achieve processing outcomes that are not accessible via traditional annealing.