Interface-Driven Orientation and Confinement in Poly(3-hexylthiophene-2,5-diyl)/Polylactic Acid/Gold Nanoparticle Composite Films for Enhanced Charge Transport

Thin films made of functional nanophases based on the semiconducting polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) and the insulating hydrophilic polymer polylactic acid (PLA), combined with functionalized gold nanoparticles (AuNPs), were investigated. Exploiting phase separation phenomena between the polymers, nanostructured morphologies were obtained, where P3HT was either confined in isolated domains or formed continuous phases, depending on the experimental conditions. Following a bottom-up synthesis of thiol-functionalized AuNPs, interconnected network systems were obtained and spin-coated together with the polymeric materials to obtain thin films of AuNPs-embedded polymeric nanophases. Combining strategies from chemistry and materials science, i.e., bottom-up synthesis of hydrophobic AuNPs and P3HT/PLA nanophase confinement, it was possible to fine-tune the nanophase confinement, enhance transport properties, and modify the orientation of the P3HT chains through interfacially driven self-assembly. The structure–property relations of the nanomaterials were investigated, morphologically with AFM and morphostructurally with synchrotron radiation-induced GIWAXS studies, evidencing that the addition of AuNPs in the blend influences the backbone orientation of P3HT, switching it from a mixed orientation to a prevalently face-on one. Electrical measurements were correlated with morphological features to assess the impact of nanoconfinement and nanoparticle inclusion on transport properties, finding that AuNPs-induced reorientation leads to a 10-fold enhancement in the blend’s electrical conductivity.