Blocked shape memory effect in negative Poisson鈥檚 ratio polymer metamaterials

Abstract

We describe a new class of negative Poisson鈥檚 ratio (NPR) open cell PU鈥揚E foams produced by blocking the shape memory effect in the polymer. Contrary to classical NPR open cell thermoset and thermoplastic foams that return to their auxetic phase after reheating (and therefore limit their use in technological applications), this new class of cellular solids has a permanent negative Poisson鈥檚 ratio behavior, generated through multiple shape memory (mSM) treatments that lead to a fixity of the topology of the cell foam. The mSM-NPR foams have Poisson鈥檚 ratio values similar to the auxetic foams prior their return to the conventional phase, but compressive stress鈥搒train curves similar to the ones of conventional foams. The results show that by manipulating the shape memory effect in polymer microstructures it is possible to obtain new classes of materials with unusual deformation mechanisms.