An Investigation on Morphology of Emulsion-Templated Polyimide Aerogel Foam Sheets

This paper discusses fabrication of polyimide aerogel foam sheets with embedded micrometer size voids (macrovoids) introduced via oil-in-oil (O/O) emulsion-templating of polyimide sol with silicone oil, followed by casting, gelation, and supercritical drying. The aerogel foam sheets contain significant fractions of mesopores (2–50 nm) inherent to polyimide aerogels and macrovoids introduced in the form of silicone oil droplets. An understanding is developed in this work to correlate sol casting conditions, sol composition, and transient viscosity growth with the macrovoid size distribution, mesopore content, and morphology of aerogel foam sheets. The study finds that the flow of sol in a doctor’s blade casting system induces coalescence of silicone oil droplets. The study also determines that the properties of the cast gel and aerogel sheet materials strongly depend on the time of sol casting, measured in terms of lead time (tlead) away from the gel point.