Meta-Aerogels: Auxetic Shape-Memory Polyurethane Aerogels

Shape-memory poly­(isocyanurate–urethane) (PIR–PUR) aerogels are low-density monolithic nanoporous solids that remember and return to their permanent shape through a heating actuation step. Herein, through structural design at the macro scale, the shape-memory response is augmented with an auxetic effect manifested by a negative Poisson’s ratio of approximately −0.8 at 15% compressive strain. Thus, auxetic shape-memory PIR–PUR monoliths experience volume contraction upon compression at a temperature above the glass transition temperature of the base polymer (T_g ≈ 30 °C), and they can be stowed indefinitely in that temporary shape by cooling below T_g. By heating back above T_g, the compressed/shrunk form expands back to their original shape/size. This technology is relevant to a broad range of industries spanning the commercial, aeronautical, and aerospace sectors. The materials are referred to as meta-aerogels, and their potential applications include minimally invasive medical devices, soft robotics, and situations where volume is at a premium, as for example for storage of deployable space structures and planetary habitats during transport to the point of service.