Meta-Aerogels: Auxetic Shape-Memory Polyurethane Aerogels

Abstract

Shape-memory\npoly­(isocyanurate–urethane) (PIR–PUR)\naerogels are low-density monolithic nanoporous solids that remember\nand return to their permanent shape through a heating actuation step.\nHerein, through structural design at the macro scale, the shape-memory\nresponse is augmented with an auxetic effect manifested by a negative\nPoisson’s ratio of approximately −0.8 at 15% compressive\nstrain. Thus, auxetic shape-memory PIR–PUR monoliths experience\nvolume contraction upon compression at a temperature above the glass\ntransition temperature of the base polymer (<i>T</i>_g ≈ 30 °C), and they can be stowed indefinitely\nin that temporary shape by cooling below <i>T</i>_g. By heating back above <i>T</i>_g, the compressed/shrunk\nform expands back to their original shape/size. This technology is\nrelevant to a broad range of industries spanning the commercial, aeronautical,\nand aerospace sectors. The materials are referred to as meta-aerogels,\nand their potential applications include minimally invasive medical\ndevices, soft robotics, and situations where volume is at a premium,\nas for example for storage of deployable space structures and planetary\nhabitats during transport to the point of service.