Abstract
In this brief review, an introduction of the underlying mechanisms for the shape memory effect (SME) and various shape memory phenomena in polymers is presented first. After that, a summary of typical applications in sensors based on either heating or wetting activated shape recovery using largely commercial engineering polymers, which are programmed by means of in-plane pre-deformation (load applied in the length/width direction) or out-of-plane pre-deformation (load applied in the thickness direction), is presented. As demonstrated by a number of examples, many low-cost engineering polymers are well suited to, for instance, anti-counterfeit and over-heating/wetting monitoring applications via visual sensation and/or tactual sensation, and many existing technologies and products (e.g., holography, 3D printing, nano-imprinting, electro-spinning, lenticular lens, Fresnel lens, QR/bar code, Moiré pattern, FRID, structural coloring, etc.) can be integrated with the shape memory feature.
Highlights
Stimulus-responsive shape switching refers to the phenomenon that the shape change in a material is induced by an externally applied stimulus [1,2,3,4,5]
Since the heating-responsive shape memory effect (SME) in most of the 3D printed polymeric items is based on Tg, and the choice of polymers for printing is still limited at present, it appears to be a very important concern in material selection for 4D printing, in which the additional D refers to the capability of shape change in 3D
Micro-features can be produced atop shape memory polymers (SMPs) via, for examples, nano-imprinting in roll-to-roll manner [59,96] or self-wrinkling [62], so that we can see some interesting phenomena at this a roll-to-roll manner [59,96] or self-wrinkling [62], so that we can see some interesting phenomena at dimensional scale, such as the structural coloring effect [79]
Summary
Stimulus-responsive shape switching refers to the phenomenon that the shape change in a material is induced by an externally applied stimulus [1,2,3,4,5]. Most polymers are heating- and chemo-responsive shape memory polymers (SMPs) as revealed in Reference [12], the actual shape memory performance varies according to the actual polymer and its processing (programming and activation) method, and environmental conditions, etc. The works presented here are based on our unpublished works
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