Shape memory behaviour of polyacrylamide/MWCNT nanocomposite hydrogel under direct and indirect stimulation

Abstract

Shape memory hydrogels are a class of smart materials with the ability of multiple shape forming. Their low stiffness is the main challenge. In this work, pure PAAm and PAAm nanocomposite shape memory hydrogels containing multiwalled carbon nanotubes (MWCNT) were prepared by in-situ radical polymerization. The presence of MWCNT guarantees an enhancement of stiffness and shape recovery of polyacrylamide (PAAm) hydrogel system as well as its recovery speed from temporary to permanent shape of nanocomposite hydrogel under indirect heat stimulation. By examining the electrical conductivity and rheological properties, the corresponding percolation threshold was obtained at 0.2 wt% of MWCNT. The results of dynamic mechanical analysis (DMA) showed that the presence of nanoparticles completely fixed the temporary shape of the PAAm nanocomposite hydrogel and increased the shape recovery up to 96%. In direct heat stimulation, by the aid of thermographic camera it was observed that the addition of 0.2 wt% of MWCNT increased the transition temperature of the nanocomposite hydrogel compared to the neat sample. In indirect heat stimulation by applying 100 V and 300 V electrical voltage, complete shape recovery was achieved in 7 min and 2.5 min, respectively.