"Twin-Chain" Hydrogels with Tailored Porosity, Surface Roughness, and Cleaning Capabilities.

The remedial conservation of cultural heritage requires advanced functional materials that span from soft matter to nanostructured formulations, whose study is relevant to different fields, ranging from cosmetics and detergency to tissue engineering. In the vast landscape of innovative materials developed to counteract artwork degradation, gels have emerged as ideal candidates for cleaning delicate and complex surfaces. More specifically, twin-chain networks (TCNs), i.e., sponge-like hydrogels obtained through spontaneous polymer-polymer phase separation and sustainable freeze-thawing, showed unprecedented cleaning performances on modern/contemporary iconic paintings, such as works by Jackson Pollock and Pablo Picasso. The key to their efficacy lies in the complex cleaning mechanism at the gel-substrate interface. Recent findings suggest that the pore size and connectivity, affecting the nanoscale tortuosity, play a crucial role in determining the gels' uptake (cleaning) ability. Nonetheless, diffusion of soil through the gel networks is only part of the complex processes that control the removal of unwanted layers from painted surfaces. A deeper understanding of the cleaning mechanism requires studying the uptake of solid particulate matter: gel adhesion and surface roughness affect the cleaning performance of a gel. In this work, TCNs with modulated porosity, obtained by mixing poly(vinyl alcohol)s (PVAs) of different hydrolysis degrees and molecular weights, were characterized through different techniques (confocal laser scanning microscopy, scanning electron microscopy, differential scanning calorimetry, and rheology) to relate porosity and structural features to the surface roughness and diffusional properties of the gels. Finally, cleaning tests on model painted surfaces revealed a clear connection between the surface inhomogeneity and the cleaning performance of the gels.