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Abstract
We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying the resulting wet spherical gels with supercritical fluid (SCF) CO2 afforded spherical aerogel beads with a mean diameter of 2.7 mm, and a narrow size distribution (full width at half maximum: 0.4 mm). Spherical PUA aerogel beads had low density (0.166 ± 0.001 g cm–3), high porosity (87% v/v) and high surface area (197 m2 g–1). IR, 1H magic angle spinning (MAS) and 13C cross-polarization magic angle spinning (CPMAS) NMR showed the characteristic peaks of urea and the isocyanurate ring. Scanning electron microscopy (SEM) showed the presence of a thin, yet porous skin on the surface of the beads with a different (denser) morphology than their interior. The synthetic method shown here is simple, cost-efficient and suitable for large-scale production of PUA aerogel beads.
Highlights
Aerogels are highly porous ultralight materials, consisting of low-density 3D assemblies of nanoparticles [1,2]
They were left in that condition for aging for 15 min. They were removed fromThey the were left in that condition for aging for min. They were removed from the mineral oil, mineral oil, solvent-exchanged with acetone (Figure 1 left) and were dried in an autoclave with solvent-exchanged with acetone (Figure left) and were dried in an autoclave with supercritical supercritical CO2 into spherical PUA aerogels (Figure 1 middle and right)
Spherical polyurea (PUA) aerogel beads were synthesized at room temperature, without the use Spherical (PUA) aerogel beads were synthesized at room temperature, without the use of surfactants, polyurea from an aliphatic triisocyanate
Summary
Aerogels are highly porous ultralight materials, consisting of low-density 3D assemblies of nanoparticles [1,2]. They can be defined as solid colloidal or polymeric networks of particles expanded throughout their entire volume by a gas [3,4]. They are formed by removing all swelling agents from a wet-gel without substantial volume reduction or network compaction. Several types of aerogels have been reported, including inorganic [5,6,7,8,9], organic (based on biopolymers [10,11,12,13] or synthetic polymers [14,15,16,17]), and hybrid inorganic/organic [18,19,20,21,22]
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