Transparent Polyimide Aerogels: Controlled Porosity via Minimizing the Phase Separation

The aerogels industry has been growing with a market capacity of 909 billion USD in 2019. Silica aerogels are the most extensively used due to their ease of synthesis. It can possess many useful properties such as high optical transparency, high-surface area, low thermal conductivity, and a wide accessible density range. However, silica aerogels are brittle and friable, making them unsuitable for many applications. Polymeric aerogels are typically much more robust but lack the uniform fine nanostructure which gives silica its exceptional properties. Herein, mechanically robust polyimide (PI) aerogels with uniform <20 nm porosity and exceptional transparency are demonstrated. Optimization was achieved by minimizing the phase separation during gelation, minimizing the light scattering, and yielding the exceptionally transparent aerogels. The aromatic PI backbone results in a high modulus while retaining a low thermal conductivities and high thermal stability. We demonstrate methods for inducing phase separation to increase the pore size and the effects on bulk properties. This study presents a better understanding of the route to producing transparent polymer aerogels.