Have you ever wondered how museums and galleries clean the paper artworks without damaging them? In recent years, the use of hydrogels for this purpose has increased in popularity. Hydrogels are an alternative to traditional wet cleaning techniques that have much lower risk of irreversible damage to the artwork. A team from a larger project involving the Italian National Research Council - Institute for Complex Systems (CNR-ISC), Sapienza University and the University of Rome Tor Vergata visited LET to use QENS to analyse hydrogels and microgels for this purpose.
Since ~2000, hydrogels have been in use for safely cleaning paper artworks for the removal of dirt deposits and to slow down cellulose degradation. They are mostly water (~95%) but with a gel-like consistency that enables them to be applied to artwork and peeled off, taking with it, the dirt. Microgels have a similar local structure to hydrogels, but where hydrogels are an extended membrane, microgels have cross links that form a more condensed structure with smaller (micro) particles.
The project leader, Dr Emanuela Zaccarelli, had the idea to replace hydrogels with microgels as the microgel can penetrate deeper into the paperwork to provide more effective cleaning in a shorter amount of time. The team then wanted to see if the performance of the microgel can be improved further by changing the compositions of the gels. For instance, certain types of salts, such as calcium acetate, can be used to form gels with improved mechanical properties, stability, and cleaning efficiency.
At ISIS, the team were using QENS to observe the polymer dynamics of hydrogels derived from gellan gum, a high molecular weight linear extracellular polysaccharide, obtained from Pseudomonas elodea. They examined hydrogels as they are easier to analyse, because their microgel counterparts can diffuse in the solution, leading to an additional QENS signal. The changes observed in hydrogels are then expected to be present in the microgels prepared with the same composition. To observe the impact of calcium ions on the gel, the team measured hydrogels at the same polymer and water concentration in the absence and in the presence of calcium acetate. From a careful analysis of the QENS spectra measured on different timescales and through a comparison with the results of computer simulations, they expect to quantify the effect of the salt on the dynamics of water and of the gellan polymer in the gel.
The goal of experiments, such as this one, is to understand which changes in the local landscape have an impact on microscopic properties and performance of the gels and use this knowledge to optimise them.
This research was funded initially by Regione Lazio through L.R. 13/08 Progetto Gruppo di Ricerca MICROARTE n. prot. A0375-2020-36515 and currently by an ERC Proof of Concept grant (MICROTECH).