A study of water mobility in hydrogels suitable for biocleaning mural paintings: a unilateral NMR study

Unilateral NMR is a powerful tool to evaluate water mobility and diffusion in gels used in a fully non-invasive and nondestructive way. Different types of gel formulations to be used as cleaning systems for wall painting were investigated. Transverse relaxation times measured in gel formulations indicate the presence of water in two environments. The water molecules with a short relaxation time may be involved in hydrogen bonding interactions and/or proton exchange with gel macromolecules, while the molecules with a longer relaxation time are free to move through the network, although self-diffusion measurements demonstrate that their translational motion is increasingly hindered as the average probability of collisions with the gel network increases. The release and diffusion of water at the gel-wall painting interface were investigated. Gellan concentration and application time of the gel may be tuned to modulate the amount and the depth of penetration of the liquid phase through the porous network. Water absorption, distribution and penetration in the support depend not only on the physical-chemical and rheological properties of the gel but also on the properties of the support to which the gel is applied. This study is part of a more extensive research effort aimed at obtaining an analytical protocol for establishing in situ the performance of cleaning systems.