Shape memory polymer nanocomposite: a review on structure-property relationship

Shape memory polymers (SMPs)are among the main groups of smart materials widely used in smart textiles and apparels, intelligent medical devices, sensors actuators, high-performance water-vapor permeability materials, morphing applications, and self-deployable structures in spacecraft. However, SMPs have some limitations: comparatively low tensile strength and stiffness, relatively low recovery stress, low thermal conductivity, inertness to electrical, light, and electromagnetic stimuli accompanied by slow responsibility and low recovery time during actuation, which often limits SMPs potential applications in high-performance field. In recent years, researchers have focused more on shape memory polymer nanocomposites (SMPNCs)than the classical composites to overcome this limitation of the SMPs, as nanofillers have a large surface area and strong interaction with polymers. This review thoroughly examines the progress in SMPNCs, including the very recent past, with a particular focus on their structure-property relationship. Considering all the SMPs, the most commonly used SMPs like polyurethane, epoxy, polycaprolactam, polylactic acid, and polyvinyl alcohol along with carbon-based (i.e., CNTs, carbon black, graphene oxide, graphene nanoplatelets, graphene quantum dots, nano-diamonds), metal oxide-based (i.e., Fe3O4, TiO2), cellulose-based (i.e., cellulose nanocrystals, nano-cellulose gel), and other nanomaterials like nano-clay, TiN, AuNRs, organic nanoparticles, silica, sepiolite, silsesquioxane, and hydroxyapatite nanofillers are discussed. The future development of SMPNCs may enhance their performance under thermal, electric, light (UV/NIR), magnetic, and solvent (pH/water)stimuli, which may open the door to more advanced applications in the field of aerospace, robotics, sensing and actuation, and biomedical.