Aerogels with 3D Ordered Nanofiber Skeletons of Liquid‐Crystalline Nanocellulose Derivatives as Tough and Transparent Insulators

Abstract

Aerogels of high porosity and with a large internal surface area exhibit outstanding performances as thermal, acoustic, or electrical insulators. However, most aerogels are mechanically brittle and optically opaque, and the structural and physical properties of aerogels strongly depend on their densities. The unfavorable characteristics of aerogels are intrinsic to their skeletal structures consisting of randomly interconnected spherical nanoparticles. A structurally new type of aerogel with a three‐dimensionally ordered nanofiber skeleton of liquid‐crystalline nanocellulose (LC‐NCell) is now reported. This LC‐NCell material is composed of mechanically strong, surface‐carboxylated cellulose nanofibers dispersed in a nematic LC order. The LC‐NCell aerogels are transparent and combine mechanical toughness and good insulation properties. These properties of the LC‐NCell aerogels could also be readily controlled.

Thermal conductivity of hygroscopic foams based on cellulose nanofibrils and a nonionic polyoxamer

“…Depending on the cellulose source and how the foams/ aerogels have been produced, the thermal conductivity of nanocellulose foams and aerogels varied between 20 and 40 mW/mK (Jelle 2011;Kobayashi et al 2014;Sakai et al 2016;Jimenez-Saelices et al 2017). To date, however, studies on the thermal conductivity of nanocellulose-based foams and aerogels are sparse and have primarily assessed the thermal conductivity of the porous materials at constant temperature and/or constant relative humidity (Silva et al 2010;Isogai et al 2011;Nguyen et al 2014;Wicklein et al 2014;Jimenez-Saelices et al 2017).…”

Facile Fabrication of Nanofibrillated Chitin/Ag2O Heterostructured Aerogels with High Iodine Capture Efficiency

“…Many other reactant systems, such as melamine–formaldehyde 6 , resorcinol–furfural 7 , cresol–formaldehyde 8 , phenol–furfural 9 , polyurethane 10 , polyisocyanate, and polyolefin 11, 12 , have been developed in later works by other researchers. Recently, cellulose or chitin have received increased attention as aerogel building blocks because of their outstanding high stiffness, low density, high aspect ratio, and large specific surface area 13–17 . Numerous reports on nanofabrillated-cellulose-based aerogels have been widely published 18 .…”

Versatile Double-Cross-Linking Approach to Transparent, Machinable, Supercompressible, Highly Bendable Aerogel Thermal Superinsulators

“…The flexibility of PVPSQ, PAPSQ, PVPMS, and PAPMS aerogels and xerogels is significantly higher than that of traditional silica 9 and metal oxide aerogels. 40 In particular, the superflexibility of PVPMS and PAPMS aerogels/xerogels has not been observed in recently reported aerogels such as PMSQ, 15 PVSQ, 16 organo-bridged polysiloxanes, [18][19][20] nanocellulose, 22,23 chitosan, 24 polymer 3,27 and silica-based organic-inorganic hybrid aerogels. 11,13 In addition, the PVPMS aerogels exhibit the similar bending flexibility but much higher elasticity against compression compared to those of a commercial phenol foam with a sufficiently low thermal conductivity of ~ 20 mW m −1 K −1 ( Figure S10).…”

“…[22][23][24] Unlike the polysiloxane-based organic-inorganic hybrid aerogels, however, they do not show elastic recovery in response to compression and bending. It is reported that polymer-based aerogels such as supramolecular aerogel, 25 poly(vinyl alcohol)-based aerogel, 3 thermoelectric polymer aerogel 26 and resorcinol-formaldehyde aerogel 27 exhibit high mechanical strength or elasticity against compression.…”