Colorless Transparent Melamine–Formaldehyde Aerogels for Thermal Insulation

Abstract

Aerogels have many unique properties such as low density and low thermal conductivity, and, in particular, transparent silica aerogels are attractive for thermal insulating windows. Practical applications of silica aerogels, however, have been limited because of their low mechanical strength, and it is still challenging to synthesize transparent and mechanically strong aerogels. Here, we report colorless transparent melamine–formaldehyde (MF) aerogels prepared via a nonaqueous synthetic strategy. The obtained transparent MF aerogel with a density of 0.18 g cm–3 shows significantly higher mechanical strength and a lower thermal conductivity of ca. 13 mW m–1 K–1 compared to conventional silica aerogels with similar density.

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.…”

Facile preparation for gelatin/hydroxyethyl cellulose‐SiO2 composite aerogel with good mechanical strength, heat insulation, and water resistance

“…In order to make the aerogel more robust, the inorganic/organic composite aerogels can be prepared by reinforcing the network skeleton structure of organic polymers using the micron or nano‐scale inorganic materials. These aerogels exhibit better strength and dimensional stability than the pure silicone aerogels, which can be used as ideal insulation, flame retardant, and shock‐absorbing material 28–30 . SiO 2 particles have been widely used in the fields of construction and engineering in recent years as a result of their advantages of controllability in size, large specific surface area, low thermal conductivity, and adsorption capacity.…”

“…These aerogels exhibit better strength and dimensional stability than the pure silicone aerogels, which can be used as ideal insulation, flame retardant, and shock-absorbing material. [28][29][30] SiO 2 particles have been widely used in the fields of construction and engineering in recent years as a result of their advantages of controllability in size, large specific surface area, low thermal conductivity, and adsorption capacity. There is a strong affinity between the functional groups of some biopolymer molecules and the surface of SiO 2 particles, which can be formed a plurality of cross-linking points to create a diversified gel network structure.…”

Highly porous melamine-formaldehyde monoliths with controlled hierarchical porosity toward application as a metal scavenger

“…After gelation and aging at 40 °C and 60 °C, the obtained monolithic gel underwent hydrothermal aging at 120 °C for 24 h, washing by solvent exchange, and finally drying from n-hexane. We employed DMF, not water, as the main solvent because methylomelamine is highly soluble in DMF and a heterogeneous network tends to form in water 17 . In addition, we used a small amount of 60 wt% nitric acid as a reaction catalyst.…”