Flexible Polyurea Aerogels: The Effect of the Polarity of the Gelation Medium on the Nanomorphology

Mechanically strong polyurea (PUA) aerogels have been synthesized in acetone from Desmodur N3300A triisocyanate, water and triethylamine (TEA) as catalyst. Curiously, the nanomorphology of PUA aerogels varies from fibrous to particulate as the density increases. Reasoning that higher monomer concentrations (as high as 0.52 M) change the dielectric properties of the medium, herein we emulate that effect by changing the solvent polarity, and we report synthesis of PUA aerogels with nanomorphologies varying from similar to those obtained in acetone (e.g., in ethyl acetate), to cocoon-like structures embedded in a fiber web (e.g., see Figure below in acetonitrile). Some of those materials are flexible, while others demonstrate low speed of sound wave propagation (198 m s ^-1 at 0.340 g cm ^-3 ) and are suitable for acoustic insulation.