Unilateral NMR to study water diffusion and absorption in stone-hydrogel systems

Highly performing cleaning systems based on hydrogels for buildings and artefacts were studied by unilateral NMR. Specifically, the release and diffusion of water from gellan gum formulations at the gel stone interface were investigated. The study was carried out by applying gel formulations to stone specimens with different porosimetric properties, namely Yellow Tuff of Via Tiberina and Lecce stone. NMR measurements and a suitable processing of data allowed the obtainment of the total open porosity, the average pore size, and the tortuosity of the stones. Properly calibrated H-1 NMR depth profiles with micrometric resolution were used to evaluate the effective volume of absorbed water, the distribution of water in porous stone specimens, and the degree of saturation. The deformation coefficient of the gel after water release was also determined. The obtained results indicated that the performance of the gel depends not only on its physical-chemical properties but also on the porosimetric properties of the stone to which the gel is applied. Therefore, the knowledge of the porosimetric properties of the material is important for selecting a suitable and highly performing gel cleaning system. (C) 2017 Elsevier Inc. All rights reserved.