Producing Crack-Free Colloid−Polymer Hybrid Gels by Tailoring Porosity

Abstract

Several mixtures obtained by ultrasonic agitation of colloidal silica with a sol solution containing tetraethoxysilane (TEOS) were used to form crack-free monoliths. The dry gels that were submitted to mercury porosimetry showed differences in behavior according to the proportion of silica colloid in the gel. For low proportions, the mercury isostatic pressure exclusively induced an irreversible compaction of material, but intrusion occurred in gels with a high proportion of colloid. This permitted the evaluation of the textural properties of intruded gels, whereas the pressurization-depressurization paths, where intrusion was prevented, provided information about their compression behavior. Specimens exhibited elastic strain, followed by yield and plastic hardening. Bulk modulus was significantly reduced as the content of silica particles in the gel was increased. This was related to the increase in free volume of the network. The yield point, which characterizes the limit of the elastic region, was taken as a reference for estimating the maximum capillary pressure of drying; the inclusion of colloidal silica progressively reduced the maximum capillary pressure occurring during the drying for all samples except those containing the highest proportion of colloid (82%). This anomalous behavior was associated with low TEOS content, which complicates the formation of siloxane bonds. Textural properties determined by nitrogen adsorption confirmed the results obtained by porosimetry. Both porous volume and pore size were gradually increased in line with the colloid content. Therefore, we offer an effective means of tailoring the derived sol-gel porosity by increasing the proportion of colloidal silica, starting from a dense microporous material to achieve a mesoporous gel with a high pore volume and reduced capillary pressure.

Behaviour of sonogels under isotropic pressure

“…These properties feature the behaviour of sonogels and sonogel based composites under mechanical stresses. A previous study on nanostructured sono-xerogels hosting silica colloidal particles in different proportions [8] showed that the curves of pressure versus sample volume did not correspond exactly to those reported for classic xerogels. One of the main structural characteristics of sonogels is that the pore size distribution is typically below the 2 nm radius that confers an elastic behaviour along a wide pressure range.…”

“…Pirard et al [6] and Alié et al [7] observed Hg intrusion in xerogels and, more recently, Mosquera et al [8] also observed this. In those cases where no intrusion is observed, the experiment results in an isotropic compression of the gel.…”

“…K and K' values were obtained from P(v) outputs of standard runs of mercury intrusion on a degassed monolithic sample according to the procedure already described [8]. Samples were pressurised to atmospheric pressure in steps of 0.2 to the fitting of the mercury to the irregularities on the surface larger than 0.1 mm.…”

“…In the case of compliant materials like light aerogels, the initial part of the curve corresponding to an elastic regime is concave downwards, and then for a plastic regime the curvature clearly reverses [3]. However, in the compression curves for more rigid gels like xerogels obtained from TEOS [8], it is not possible to determine this typical change in curvature from a simple inspection. In these specimens, the yield point must be calculated from tedious sequential compressive experiments in which the pressure is progressively increased.…”

Conservation of stony materials in the built environment

“…There is also a significative research in consolidation promote by microorganisms by the production of calcium carbonate in limestones and concrete (Rodriguez-Navarro et al 2003;Fernandes 2006;Jimenez-Lopez et al 2007;De Muynck et al2010;De Muynck et al 2011;Peihao and Wenjun 2011;Rodriguez-Navarro et al 2012). There have been research studies in the possible application of nanotechnology, and some examples include using nanoparticles of calcium and magnesium hydroxide and carbonate (Baglioni and Giorgi 2006;López-Arce et al 2011) and addition to polymeric products of nanoparticles of silica (Mosquera et al 2003;Kim et al 2009;De Ferri et al 2011;Tulliani et al 2011;Xu et al 2012) and other oxides . Penetration being generally an important issue in the case of consolidation, one of the alternatives that have been proposed is impregnation by a monomer and ''in situ'' copolymerisation afterwards (Vicini et al 2002;Cardiano et al 2002).…”