Effect of the porosity and microstructure on the mechanical properties of organic xerogels

Abstract

The synthesis of resorcinol-formaldehyde (RF) xerogels is versatile enough to provide materials with custom pore size distributions in the meso/macroporous range. Specifically, seven xerogels were synthesised by changing the pH of the same RF solution, from pH 3 to pH 6. The resulting materials presented meso/macropore size distributions with average pore sizes from <5 to 510 nm, as determined by Hg intrusion and N 2 adsorption. Most of the RF xerogels had very similar geometric densities, except for the gels obtained at the two highest pH values, which were more dense. Both flexural and uniaxial compression tests were carried out to determine the dependence of strength and stiffness on the porosity of the xerogels. The results followed a power-law relationship between the mechanical properties and the density of the materials. However, two series of RF xerogels were found to fit such law independently, with the gels obtained at the three most acidic pH values (pH 3-4) showing unexpectedly high compression moduli. Further characterisation of the xerogels microstructure revealed the existence of rod-like microstructures that would bear most loads during the compression tests. These microstructures would act as struts that, once broken, would cause the catastrophic failure (bursting) of the xerogel.

Electromagnetic interference shielding in lightweight carbon xerogels

“…This behavior indicates the brittleness of the carbon xerogel, which can break suddenly under external loading without necking, unlike ductile materials. Experimentally, a maximum depth of ∼ 0.05 mm was realized, at which the spherical indenter applied a maximum external force of ∼ 20 N. The calculated average value of Young's modulus was found to be 384.14 ± 21.5 MPa, which is in sufficient agreement with the literature data, ranging between 80 MPa and 1 GPa [32,33]. Young's modulus value suggests that the carbon xerogel can withstand prolonged mechanical stress owing to its robustness while exhibiting repeatable and reproducible EMI shielding properties.…”

Insights into the Micromechanics of Organic Aerogels Based on Experimental and Modeling Results

“…While investigations on the structural and the thermal properties of RF aerogels have been reported by several authors, [ 2–8 ] reports on their mechanical properties are rare. [ 9 ] Pekala et al [ 10 ] investigated the dependence of the morphological aspects of RF aerogels on their mechanical performance. Typically for aerogels, like many other open‐porous materials, the power law scaling relationship between the Young's modulus E and the bulk density ρ , is often explored in the literature with their mechanical properties.…”

Acoustic Fractional Propagation in Terms of Porous Xerogel and Fractal Parameters

“…In order to carry out fair comparisons and exemplary discussions in which usual xerogels are involved, some chitosan xerogel explanation samples were processed in the analogous conditions as the hydrogels mentioned in Section 4; all were denoted with the letter F and a certain number of indices [18][19][20]. In other words, we have obtained the SEM experimentally realized images of several different xerogels, each having diverse degrees of porosity [21]. In the following section, however, we will present only the picture that proved to be the most representative [22][23][24].…”