Water confined in nanopores: spontaneous formation of microcavities

Molecular Dynamics simulations of water confined in nanometer sized, hydrophobic channels show that water forms localized cavities for pore diameter ~ 2.0 nm. The cavities present non-spherical shape and lay preferentially adjacent to the confining wall inducing a peculiar form to the liquid exposed surface. The regime of localized cavitation appears to be correlated with the formation of a vapor layer, as predicted by the Lum-Chandler-Weeks theory, implying partial filling of the pore

Noninvasive monitoring of moisture uptake in Ca(NO3)2-polluted calcareous stones by1H-NMR relaxometry

NMR transverse relaxation time (T2) distribution of 1H nuclei of water has been used tomonitor the moisture condensation kinetics in Ca(NO3)2·4H2O-polluted Lecce stone, a calcareous stone with highly regular porous structure often utilized as basic material in Baroque buildings. Polluted samples have been exposed to water vapor adsorption at controlled relative humidity to mimic environmental conditions. In presence of pollutants, the T2 distributions of water in stone exhibit a range of relaxation time values and amplitudes not observed in the unpolluted case. These characteristics could be exploited for in situ noninvasive detection of salt pollution in Lecce stone or as damage precursors in architectural buildings of cultural heritage interest

Evidence of Temperature-Induced Subdiffusion of Water on the Micrometer Scale in a Nafion Membrane

To investigate the topological features of proton transport in perfluorosulfonic membranes, we performed time-dependent (t)H NMR pulsed gradient spin-echo experiments on four samples of Nafion-115 with lambda = 0.5, 3.2, 5.8, and 12.4 water molecules per sulfonic group at different temperatures ranging from 278 to 348 K. A subdiffusive behavior of water, = 2D(alpha)t(alpha) with 0.75 < alpha < 1, was observed above 320 K for each of the four samples. The onset of water subdiffusion with increasing temperature, basically independent of membrane hydration, supports the hypothesis of a drop in dimensionality for the diffusion space. Diffusion-diffraction effects on the NMR echo-signal attenuation confirm that proton displacement is restricted because of an interconnected pore structure With it coherence length of similar to 1 mu m, which depends on temperature and water content

High density water clusters observed at high concentrations of the macromolecular crowder PEG400

What happens to water in crowded environments? A detailed understanding of how water is affected by the presence of a crowding agent is still lacking. In the present work, we focus on macromolecular crowding. In particular, we study aqueous solutions of a macromolecular crowder with many industrial applications, namely, poly-(ethylene) glycol with a mass weight of 400 g/mol (PEG400), at compositions ranging from infinite dilution to polymer weight fractions of 0.95 by means of molecular dynamics simulations and 1H DOSY-NMR experiments. Our data show that water density is severely affected by the presence of macromolecular chains at all concentrations, and is, on average, always higher than the bulk water density as a result of the superimposition of the hydration shells of the polymer chains. Moreover, the combined computational-experimental approach concurs well with the following scenario: water still forms clusters even within the solutions at the highest concentration, rather than saturating all available hydrophilic sites of the polymeric chains, indicating a clear predilection for water-water interactions

Moisture content and strain relation in wood by Bragg grating sensor and unilateral NMR

The paper describes a low-invasive experimental apparatus designed for the accurate determination of mechanical deformation and moisture content (MC) relationship on macroscopic wood samples. The device is particularly indicated for monitoring wooden handwork whose mechanical deformation is especially critical in relation to its role such as, for example, works of art or architectural works. The MC of wood is measured with a portable single-sided NMR probe and mechanical deformation by a fiber Bragg grating optical sensor. The data obtained are of high accuracy, despite the dimensions of the sample. The methodology provides an effective tool for investigating the dynamic relation between environmental relative humidity, MC, and shrinking-swelling of wood. Adsorption results collected for longitudinal deformation in silver fir (Abies alba Mill.) are presented to show the sensitivity of the optical sensor. Interesting findings include the detection of two different mechanisms of elongation and the time evolution of water mobility versus hydration and strain

The Use of Portable Single-Sided Relaxometry and Laboratory Imaging NMR Devices in Stone Conservation

none5Two nuclear magnetic resonance (NMR) devices, a standard imaging apparatus and a portable single-sided relaxometer (with geometry that allows non-destructive in-situ relaxation measurements on samples of any dimensions), were used to assess the hydrophobic performance of an acrylic polymer (Paraloid B-72) applied as a trichloromethane (chloroform) solution on a biocalcarenite (Lecce stone). The NMR images and relaxation time distribution functions of samples characterized by different treatments were acquired for different water absorption and measurement sequences. Samples were analyzed both fully saturated and during the capillary water absorption. The relaxation results have been compared with NMR images of internal sections of the same samples in the same absorption conditions. In spite of the instrumental and physical differences of the two devices (the singlesided device was tuned to detect the signal from a sensitive volume that is only a small portion of the entire sample, located in the first 2 mm below the surface), the experimental results of relaxometry and imaging are in very good agreement. The comparison allows the assertion to be made that the single-sided NMR technique is a powerful tool for in-situ evaluation of water-repellent treatments used for consolidation and/or protection of stone artifacts.mixedM. Camaiti; C. Casieri; F. De Luca; P. Fantazzini; C. TerenziM. Camaiti; C. Casieri; F. De Luca; P. Fantazzini; C. Terenz

The use of portable single-sided relaxometry and laboratory imaging NMR devices in stone conservation

Two nuclear magnetic resonance (NMR) devices, a standard imaging apparatus and a portable single-sided relaxometer (with geometry that allows non-destructive in-situ relaxation measurements on samples of any dimensions), were used to assess the hydrophobic performance of an acrylic polymer (Faraloid B- 72) applied as a trichloromethane (chloroform) solution on a biocalcarenite (Lecce stone). The NMR images and relaxation time distribution functions of samples characterized by different treatments were acquired for different water absorption and measurement sequences. Samples were analyzed both fully saturated and during the capillary water absorption. The relaxation results have been compared with NMR images of internal sections of the same samples in the same absorption conditions. In spite of the instrumental and physical differences of the two devices (the single-sided device was tuned to detect the signal from a sensitive volume that is only a small portion of the entire sample, located in the first 2 mm below the surface), the experimental results of relaxometry and imaging are in very good agreement. The comparison allows the assertion to be made that the single-sided NMR technique is a powerful tool for in-situ evaluation of water-repellent treatments used for consolidation and/or protection of stone artifacts

Detection of magnetic environments in porous media by low-field 2D NMR relaxometry

The 2D (1)H NMR correlation maps of longitudinal (T(1)) and transverse (T(2)) relaxation times prove sensitive in monitoring the distribution of magnetic pore environments in porous systems. The comparison with MOssbauer data establishes a direct correspondence between the susceptibility-induced effects observed in the T(1)-T(2) maps for pore-filling water and the Fe(III)-bearing magnetic compounds. (C) 2010 Elsevier B.V. All rights reserved

Application and Monitoring of Oxidative Alginate&ndash;Biocide Hydrogels for Two Case Studies in &ldquo;The Sassi and the Park of the Rupestrian Churches of Matera&rdquo;

The removal of biological colonization on building materials of cultural heritage is a difficult challenge, as the treatment must completely eliminate the biological patina without altering the treated substrate and possibly delaying new colonization. With the aim of searching for systems to minimize the biocide impact on the substrate, the environment and the operators, different alginate&ndash;oxidizing biocide hydrogels were previously tested and optimized in the laboratory and here selected for application in situ. The churches &ldquo;San Pietro Barisano&rdquo; and &ldquo;Madonna dei Derelitti&rdquo;, located in the Sassi of Matera (UNESCO World Heritage Site in Basilicata region, Italy), were chosen as case studies. They differ in terms of both the environmental conditions and the microorganisms responsible for colonization. Colorimetric measurements and microscopic investigation proved the efficacy of biocide hydrogels in removing biopatinas and in restoring the original chromaticity of the selected treated surfaces of both sites. After the biocidal treatments, new protective acrylic coatings were applied to prevent recolonization and minimize the loss of material grains. Samples collected, immediately after and two years later, established the absence of biological colonization, demonstrating the long-term efficacy of the proposed restoration protocol