Transparent, mechanically strong, thermally insulating cross-linked silica aerogels for energy-efficient windows

Polyurea-crosslinked biopolymer aerogel beads

“…That trend was considered as an indication that PUA entered secondary particles, coated primary particles and lled the space within secondary particles. 37,40 As expected, particle radii were bigger compared to native alginate aerogels; the more PUA accumulates on the network, the larger the radius of the particles. Very similar trends were observed for chitosan-derived materials.…”

“…This has been rectied recently, by synthesizing polyurea/polyurethane-crosslinked alginate (X-alginate) aerogels, 37 via reaction of a preformed calcium alginate network with an aliphatic triisocyanate that was introduced, post-gelation, to the pores of the wet gel via diffusion, in analogy to the crosslinking of silica and other inorganic aerogels. 18,19,[38][39][40] The reaction formed urethane groups on the surface of the alginate framework, and a polyurea (PUA) network connecting those urethane groups, resulting in a conformal nano-thin lm of PUA around the entire alginate network. Although X-alginate aerogels are essentially copolymers, they are different from literature materials based on: (a) mixtures, blends, or composites of polyurethanes and alginates, (b) polyurethane/alginate copolymers, or (c) products from urethane bond formation between alginates and isocyanates.…”

Evaluation of Polyurea-Crosslinked Alginate Aerogels for Seawater Decontamination

“…Expanding the polymer-crosslinked (X-aerogel) technology that was initially developed with silica [ 30 , 31 , 32 , 33 ], and other metal oxide aerogels [ 34 , 35 , 36 , 37 , 38 ], we recently introduced a new class of X-aerogels based on polyurea-crosslinked biopolymers (referred to as X-alginate and X-chitosan aerogels) [ 39 , 40 , 41 ]. X-aerogels are prepared from pre-formed wet-gel networks (of an inorganic oxide or a biopolymer) via reaction of the functional groups on the surface of their skeletal framework (e.g., –OH or –NH 2 ) with a suitable monomer (e.g., a multifunctional isocyanate).…”

Engineering mesoporous silica for superior optical and thermal properties

“…As commonly seen in blue-tinted and opaque aerogel specimens, pores greater than 20-25 nm in diameter cause larger haze at shorter wavelengths due to Rayleigh scattering. 9,[27][28][29]49 The TEOS1: MTES:0.5TMCS ambigel samples featured this phenomenon with decreasing transmittance and haze increasing to 4.1% at wavelengths approaching 400 nm, giving the samples a slightly blue tint. On the other hand, the TEOS1 and TEOS1:MTES ambigel samples displayed transmittance greater than 95% and haze below 3.1% and 2.0%, respectively, throughout the visible range.…”

“…A number of aerogel studies have demonstrated low thermal conductivity but only in partially transparent monolithic aerogels. [27][28][29] Supercritically dried silica aerogels for solar thermal receivers exhibited transmittance >90%, but measured thermal conductivity was not reported. 7,30 Nanoparticle synthesis approaches seem to produce transparent monoliths with controlled pore size (<5 nm), but with porosities of ∼50%, low thermal conductivity is not expected.…”