Macromolecules, Vol.42, No.1, 273-280, 2009
Combined One-Way and Two-Way Shape Memory in a Glass-Forming Nematic Network
Past research in the field of shape memory polymers has led to significant advancements in the areas of so-called one-way and two-way (reversible) shape memory. While one-way shape memory polymers allow indefinite fixing of a temporary shape until triggered thermally to recover to an equilibrium shape, two-way shape memory polymers feature muscle-like contraction on heating and expansion on cooling under tensile load. the latter anomalous elongation occurring due to an ordering transition. Previously, reversible actuation has been reported for liquid crystalline elastomers featuring a monodomain (uniformly aligned) structure, suggesting that such alignment is required for actuation. In this work, we have prepared a glass-forming polydomain nematic network that combines reversible actuation associated with a polydomain-monodomain transition with lower temperature one-way shape memory centered at T-g. To test separability of these phenomena, distinct deformations were achieved and temporarily fixed by (1) cooling through the isotropic-nematic transition under tensile load, (2) further bending the sample isothermally above T-g, and (3) cooling below T-g. Subsequent heating led to complete and sequential recovery of the same deformations in reverse order. Applications in multistage deployment of structures are envisioned.