Fabrication and Characterization of Re-Entrant Honeycomb Polyurethane Aerogels
Aparna Agrawal, Piljae Joo, Nicholas Teo, Sadhan Jana
Abstract
In this work, polyurethane aerogels are fabricated in re-entrant honeycomb forms to achieve auxeticity and much higher flexibility than corresponding aerogel monoliths. For this purpose, a set of re-entrant honeycomb-shaped hollow molds is first printed from high-impact polystyrene (HIPS) using a fused filament fabrication technique and subsequently filled with polyurethane sol synthesized from an aliphatic triisocyanate and a diol selected from among butanediol, pentanediol, hexanediol, or octanediol. A sol–gel transition process yields the gel in a re-entrant honeycomb shape, which is isolated by dissolving the HIPS mold and supercritically dried using carbon dioxide. The effects of diol chain length on the properties of aerogels, such as bulk density, pore size, and tensile properties are investigated. The auxetic aerogels show different deformation behavior and much higher elongation at break than dogbone-shaped aerogel monoliths. Such unique properties of auxetic structures can extend applications of aerogels as acoustic absorbers and smart bandages that require high porosity, tunable pore structures, and high flexibility.