Unveiling Localized Plasmonic Activation comparing Photochemically and Thermally Initiated Polymerization

In this paper, we introduce a chemical approach to spatially investigate the energy transfer around nanoparticles excited by fs-pulsed illumination in near-infrared. Free radical acrylate polymers that can crosslinked either by photochemical or thermal pathway are used under the same illumination conditions on gold nanotriangles. The objective is to disentangle between photoinduced and thermal polymerization using the same acrylate chemistry. In photochemical regime, local photopolymerization is observed at the apex of the nanotriangles with spatial control depending on the excitation polarization. For the thermal polymer, at moderate power, nanometer-sized polymer lobes are observed on the apexes of the triangle, their position depending also on the direction of polarization. At higher power, anisotropic melting of the gold within the gold nanotriangles was observed, also depending on incident light polarization. These results are compared with theoretical calculations using modified three-temperature model, to study the nanotriangle particles time and space heat distribution. This new methodology reveals that ultrafast (< 300 fs) energy exchange can occur between the nanoparticle and the surrounding medium before temperature homogenization within the nanoparticle. Our results demonstrate the possibility to generate extremely localized nanoscale energy sources able to trigger thermal chemical reactions. We discuss the possible mechanisms beyond this energy transfer. This fundamental breakthrough opens up many new perspectives in nanofabrication based on thermally polymerizable formulations.