Novel large-scale PDA/rGO free-standing nanofilms—perspectives in photoelectronics

Polydopamine free-standing films form at the air–water interface through the self-assembly of dopamine oxidation products, creating large-scale, nanometer-thin films with remarkable mechanical properties and a two-dimensional structure. This experiment aimed to develop a PDA/rGO nanocomposite transferable onto almost any surface, offering potential for targeted functionalization. Our research revealed unexpected electronic and photonic effects arising from the distinctive structure and properties of the PDA films.

This approach utilized a novel one-pot synthesis method with boric acid as an antioxidant. The process led to the formation of 2D-like nanocomposite films of PDA and rGO. Their morphology was characterized using SEM and AFM, while their chemical composition was analyzed with UV-vis, Infrared, Raman Spectroscopy, and XPS. Boric acid enhances the mechanical properties of PDA and is crucial in reducing GO. This synthesis method harnessed the synergy of these processes, enabling the nanocomposite to be transferred onto various surfaces, creating possibilities for advanced photoelectronic applications.

The conductivity and light-interaction tests were noteworthy. Sensitive 4-Point Probe measurements revealed a decrease in the conductivity of PDA/rGO films under mild irradiation (white LED, UV light). Notably, these changes are reversible and quantifiable, attributed to structural and morphological alterations under light activation. Time-resolved reflectivity was employed to study the contraction and relaxation of the film during light on/off cycles. Unlike pure PDA, PDA/rGO films respond primarily to thermal expansion rather than moisture adsorption/desorption. This results in a significantly faster response compared to PDA, enabling the creation of expansive and contractive films through a simple synthesis process. Conductive AFM measurements revealed a complex electronic phase nanostructure, consisting of higher-conductivity domains surrounded by a nanocomposite polymer matrix with lower but notable conductivity.

These findings, although preliminary, open pathways for photoelectronic applications and offer insights into controlling the intermolecular interactions of PDA within composite materials.