Silica–Resorcinol–Melamine–Formaldehyde Composite Aerogels as High-Performance Thermal Insulators

Abstract

Here, we report the gelation and supercritical drying of ethanol-based silica–resorcinol–melamine–formaldehyde (RMF) composite aerogels with relative concentrations of initial reagents ranging from neat silica to neat RMF alcogels. The as-prepared materials are subsequently supercritically dried with carbon dioxide. Their properties include a thermal conductivity in the 15–20 mW·m –1 ·K –1 range even with a silica content as low as 20% wt . The possible reasons behind this interesting insulation performance and the mechanisms leading to the underlying gel structure are discussed in depth. A focus is made on the different gelation modes happening between the RMF and silica phases, from a coating of silica surfaces with RMF species to discontinuous RMF particles within a silica backbone and a continuous RMF backbone with isolated silica particles. The implications in terms of mechanical properties and thermal conductivity are elaborated upon. The initial ratio of silica–RMF species in this ethanol-based synthesis affects the micro- and macrostructure of the composites, resulting in materials with drastically different pore structures and thus an interesting array of possibilities for a new class of silica-organic composite aerogels, based on a sol–gel process.

Low energy buildings: multifunctional strategies and solutions

“…The experiment was carried out in 2 partslaser light ray projection on the screen without aerogel and ray projection filling Aerogel LUMIRA® LA 1000 CABOT (Civioc et al 2022) (translucent and hydrophobic aerogel granules ranging in size from 70 μm to 4 mm, thermal conductivity 18 mW/(mK)) in Fresnel lens construction with 7 cm aerogel layer between Fresnel lens and focus point. What mechanical exposure can be on aerogel?…”

“…Experimental setup. 25 ml of Aerogel LUMIRA® LA 1000 CABOT (Civioc et al 2022) (translucent and hydrophobic aerogel granules ranging in size from 70 μm to 4 mm, thermal conductivity 18 mW/(mK)) was measured and placed in a glass jar. An example of aerogel was taken for testing under the microscope with 40 x zoom to take pictures of aerogel before mechanical exposure (Guo et al 9021).…”

“…Many adaptive materials are mimicked from nature, for instance, conifer cones that have repetitive opening-closing cycles and structural properties to respond to humidity. Civioc et al(Civioc et al 2022) classified the materials into four areas: temperature-reactive materials, light-reactive materials, humidity-reactive materials, and carbon dioxide-reactive materials. The author classifies 13 smart materials, and 13 adaptive materials and lists their stimulus.…”

Mechanically Strengthened Aerogels through Multiscale, Multicompositional, and Multidimensional Approaches: A Review

“…[ 212 ] Consequently, numerous polymer‐based aerogels have been reported, and can be synthesized by varying the phenolic resin chemistry (phenol‐furfural (PF), [ 34 ] cresol‐formaldehyde, [ 32 ] melamine‐formaldehyde, [ 31 ] ) based on the polymer type, such as polyurethane (PU), [ 35 ] polyurea, [ 91 ] polybenzoxazine, [ 35 ] poly(vinyl alcohol), [ 213 ] and PI's, [ 16 ] and based on soluble polymers (polystyrene (PS), [ 214 ] polyacrylonitrile, [ 215 ] and PEDOT:PSS). Most of the polymeric aerogels contain polymer chains cross‐linked by covalent bonds, such as RF, [ 216 ] PF, [ 33 ] and PI aerogels. [ 217 ] RF aerogels are synthesized by addition–polycondensation, which can be performed under acidic and basic pH conditions.…”

Characterization and Fabrication of Xerogel Polymeric Nanocomposites and Multifunctional Applications

“…XG is a porous, architectured material emanating from varying drying strategies of wet gels . Thus, the enchanting and peculiar attributes of these porous materials are garnered from the peculiar exibility as well as resilience of the sol-gel fabrication procedure, garnered in synergy with either ambient drying (X-G) or supercritically a liated drying (A-G) [81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100]. As already elucidated, these substrates have been fabricated from varying precursors, like carbon, silica, and biopolymeric entities and possessing differing biological, physical, chemical, and mechanical, attributes, relative to varying parameters, including precursoral substrates, solvent medium, as well as drying parameters [101][102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120].…”