Ambient pressure dried resorcinol-formaldehyde (RF) organic aerogels are usually hard and brittle with Young's moduli in the range of 1-2 MPa, strengths of about 100 kPa and densities in the range of 0.2 to 0.4 g cm À3 . Modifications of the classical sol-gel synthesis route, transform these brittle materials into rubber-or cork-like flexible aerogels. We observed that in a small window of process parameters, the aerogel density decreases by an order of magnitude as well as the Young's moduli and the compression strengths. These new types of RF aerogels are elastically deformable by more than 40% in an almost reversible manner. In this paper we describe the effects of various sol-gel parameters on the flexibility, such as resorcinol to water and catalyst molar ratio and the pH of the initial solution. The aerogels are characterized with respect to the envelope density, stress-strain behavior and microstructure as observed from SEM fractographs. The chemical structure and structural differences arising between brittle and flexible RF aerogels were studied by recording 13 C-NMR spectra.

In the presented study, a sulfur infiltrated ultra-microporous carbon aerogel as a composite cathode for lithium sulfur batteries is developed and investigated.

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Four types of resorcinol-formaldehyde (RF) aerogels, stiff, brittle, low-flexible, and super-flexible are studied in this work. Despite several studies on mechanical properties on RF aerogels their response when exposed to compressive loading and their fracture behavior are not well investigated. Here, we cover aerogels with a very broad density range of 0.08-0.3 g cm -3 and compressive moduli from 0.12 to 28 MPa. We relate the microstructure of the synthesized aerogels and their behavior under uniaxial compression. Additionally, this work is the first, to our knowledge, to implement the usage of digital image correlation for characterizing the deformation of RF aerogels. The comparison of surface strain distribution of four types of aerogels provides an insight to their reaction on compressive loading.