Soft Report - Dipartimento di Fisica - Sapienza

Scientific Report – Self Assembly, Clustering, Structural arrestNon-invasive 1 H-NMR in porous materials of artistic interestNuclear Magnetic Resonance of 1 H-nuclei of waterconfined in porous media has become anirreplaceable tool for quantitative characterization ofthe structure of porous media. Proton relaxationexperiments allows evaluation of the equilibriumnuclear magnetization and extraction of distributionsfunctions of the relaxation times (T 1 and T 2), whichin fully water saturated condition may be interpretedin terms of porosity and “pore-size” distributions,respectively. The ability to use water molecules toexplore the pore space makes NMR methodsespecially appropriate for studying materials ofCultural Heritage interest. In fact, porous materials(i.e. concrete, mortar, stone, wood) can absorb orrelease water in response to thermo-hygrometricenvironmental modifications and their properties aregreatly affected by moisture content. Moreover,trapped water can dissolve the components ofporous media, altering their porosity andtransporting air pollutants inside the pore space,causing corrosion and micro-fractures. Therefore, theknowledge of capillary properties and porosity ofartworks materials is essential for the evaluation ofthe conservation state and suitable non-destructivediagnostic techniques are required. Recently, all theNMR capability of studying porous systems hasbecome available for Cultural Heritage applications,thanks to the development of portable surfaceprobes such as the mq-ProFiler. Various are thetopics concerning the field of science for CulturalHeritage explored by single-sided NMR, some ofwhich are reported in the following.Determination of moisture fraction in wood. Themobile NMR probe has been used as a non-invasivetool for water content analysis on wood samples. Theporosity index, expressed as the fraction of thesensitivity volume of the probe occupied by waterhas been proposed as an alternative to moisturecontent index, namely the amount of water masswith respect to the mass of dried sample. In principlethe method can be applied to any kind of porousmedia that has no detectable proton signal from therigid matrix as, for instance, in building materials. Inwood, where proton signal can be detected also fromcellulose or other macromolecular components, someconsiderations and artifices have been proposed foreliminating this contribution. This method hasallowed performing moisture volume fraction analysison wood samples characterized by different woodspecies, cutting and moisture content. The NMR datahave succesfully been compared with those obtainedby the gravimetric method.References[1] Casieri C., Senni L., Romagnoli M., SantamariaU., De Luca F., J. M. R., 171 (2004) 363-372.[2] Casieri C., Senni L., Romagnoli M., SantamariaU., De Luca F., in 8th Int. Conf. on “Non-destructiveTesting and Microanalysis for the Conservation of theCultural and Environmental Heritage”, 15-19 May2005, Lecce. ISBN 88-89758-00-7.AuthorsL. Senni (a,b), C. Casieri (a,c) and F. De Luca (a,b).NMR evaluation of hydrophobic treatments forstone conservation. The aim of this experimentwas to check the ability of NMR methods toquantitatively follow the absorption phenomenonunder different wettability conditions of the internalpore surfaces in “Lecce Stone”. A hydrophobicpolymer (PB72) has been applied through one face ofeach sample and relaxation data have been takenover the course of time without interrupting theabsorption process, simply by keeping the portabledevice on the surface opposite to the absorption. Themain experimental evidence was that for a sampletreated with a high amount of PB72 (478 mg in 3%(w/w) chloroform solution) when the absorption faceis the untreated one (Fig. 1a) initially the capillaryrise of water is reduced by the hydrophobic productand limited to smaller pores or to larger ones onlypartially filled with water. However, after the firsthours of absorption, the water molecules find a waythrough the polymeric barrier and invade all the porespace available at normal pressure conditions.Instead, when the absorption face is the treated one(Fig 1b), the signal density distributions are limitedto only the region of smaller T 2 for every absorptiontime, indicating that the larger pores throughoutmuch of the sample have become somewhat waterrepellent.The results have been confirmed byMagnetic Resonance Imaging analysis, showing thatthe single-sided technique is a powerful tool for insitu evaluation of water-repellent treatments usedfor consolidation and/or protection of stone artifacts.(a)(b)Fig. 1: Water uptake kinetics in 2D visualization forthe time evolution of the T 2 distribution through theuntreated face (a) and measurement from thetreated one (b) for the treated sample.References[1] Bortolotti V., Camaiti M., Casieri C., De Luca F.,Fantazzini P., Terenzi C., JMR, 181 (2006) 287-295.[2] Camaiti M., Casieri C., De Luca F., Fantazzini P.,Terenzi C., Studies in Conservation, (2007).[3] Casieri C., De Luca F., Fantazzini P., J. Appl.Phys. 97(4) 043901 (2005) 1-10.Authors:C. Terenzi (a,b), C. Casieri (a,c) and F. De Luca(a,b).(a) CRS SOFT-INFM-CNR, Roma, Italy(b) Dip. di Fisica, Univ. di Roma La Sapienza, Roma,I(c) Dip. di Fisica, Università di L’Aquila, L’Aquila, ISOFT Scientific Report 2004-0698