Driving and manipulating polymer degradation in nanocomposites via photothermal heating of the particle*

We are interested in thermally-driving chemical reactions in small volumes within a solid material, where diffusion of reactants and products are limited. Such experiments are achieved by photothermally heating metal nanoparticles incorporated within a polymer, which creates significant heat generation at the particle and an inhomogeneous steady state temperature distribution across the solid. Specifically, polymer far from any particle is cool while in contrast, local regions surrounding a particle experience temperatures up to few 100s deg. C. Utilizing polymer degradation as a test reaction creates a detectable product as a permanent record of the temperature profile and, if localized, forms defects which dramatically alter mechanical properties. In general, manipulating the connection between the fraction of chemical degradation and mechanical strength as an object deteriorates is important for plastic waste management where microfragmentation may either be harmful or beneficial depending on the remediation strategy. Polyethylcyanoacrylate (PECA) degrades by depolymerizing and in confinement the monomer will repolymerize to form oligomers. Photothermal heating of PECA exhibits heterogeneous degradation, including defect formation and synthesis of a carbonaceous by-product localized around each particle. Polyethylene (PE) degrades via thermo-oxidative processes that rely on the presence of oxygen and pre-existing defects in addition to heat; consequently, photothermal heating of PE demonstrates homogeneous degradation due to the distributed nature of the reaction pathway.