Scalable Synthesis and Dynamic Mechanical Characterization of Multifunctional Polymer Aerogels

Aerogels are low-density nanoporous solids containing hierarchical three-dimensional networks of nanoparticles pursued primarily for thermal and acoustic insulations and often for functionalization purposes. This work presents scalable sol-gel synthetic routes and characterization of various polymer aerogels including polyurea, poly(isocyanurate–urethane) and polybenzoxazine aerogels. The first part of this thesis deals with a family of ambient-dried ductile polyurea aerogels with exceptional sound transmission loss characteristics (e.g., over 30 dB within 1 to 4 kHz at bulk density 0.25 g/cm3 and 5 mm thickness). This uncommon behavior breaks the empirical “Mass Law” nature of the most conventional acoustic materials. Following an analytical approach using Biot's dynamic theory of poroelasticity, the acoustic properties of the aerogels are modeled and the results are compared with the experimental observations, to construct a design platform for the future aerogel based acoustic thin panels. In the second part, the fabrication of a family of low-density, ambient-dried and hydrophobic poly(isocyanurate–urethane) aerogels derived from a triisocyanate precursor is reported. Those aerogels are highly-stretchable and have a Poisson's ratio of only 0.22. Under dynamic conditions, their mechanical properties (e.g., mechanical strength) are three orders of magnitude stiffer than their quasi-static results. These scalable and flexible aerogels have great potentials in engineering applications including damping, energy absorption, and substrates for flexible devices. Lastly, this thesis ends with the synthesis and characterization of ambient-dried polybenzoxazine aerogels as a high-performance polymeric aerogel with strong and robust thermomechanical properties at elevated temperatures. Those aerogels are inherently flame-retardant and superhydrophobic over the entire bulk density range. In addition, they are mechanically strong with strengths (e.g., 1 MPa at 0.24 g cm−3 at room temperature) higher than those of other highperformance aerogels of similar density, including polyimide and polyamide (Kevlar-like) aerogels as well as polymer cross-linked X-silica and X-vanadia aerogels, at a significantly lower cost which makes them suitable for various industrial applications including high performance structural and thermal protection applications.