Sequential and selective shape memory by remote electrical control

Abstract

Shape memory (SM) materials have been widely investigated for several years. Most polymers present SM behaviour based on their thermo-mechanical properties. However, they are usually stimulated by an external heating source, hindering their industrial application. The addition of carbon nanotubes (CNT) allows turning conventional SM polymers into electro-active actuators. In this regard, the resistive heating by the Joule effect is considerably fast with a low energy cost.

The most used epoxy resins cured at high temperature are based on diglycidyl ether of bisphenol A (DGEBA) cured with aromatic amine hardeners, such as diaminodiohenylsulfone (DDS) and 4,4′diamine-diphenylmetane (DDM). In this work, they were synthesised with modification of the epoxy/amine ratio to vary the crosslinking density of networks so as to build up different viscoelastic properties in order to tailor their SM behaviour. Electrically conductive nanocomposites were manufactured by adding a CNT percentage above the percolation threshold.

A comparison of SM behaviour stimulated by traditional convection and resistive heating was carried out, confirming the higher recovery ratio, speed, and applicability of the electrical stimuli. In addition, the configuration of electrodes allows the design of self-deployable materials with remote control. In this way, the most common dual-shape SM polymers (one permanent shape and one temporary shape) can easily develop several stable temporary shapes. Moreover, the electrical remote control provides sequential and selective actuators, enhancing their performance for developing smart structures with shape memory capability.