A Brief Review of the Shape Memory Phenomena in Polymers and Their Typical Sensor Applications

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.

Influence of Long-Term Storage on Shape Memory Performance and Mechanical Behavior of Pre-stretched Commercial Poly(methyl methacrylate) (PMMA)

“…A full shape memory cycle includes two steps, namely programming, which is to fix the temporary shape, and recovery, which is to apply the stimulus to active the SME. From a real engineering application point of view, such as in active disassembly [31,32], deployable structures [33] and anti-counterfeit engineering application point of view, such as in active disassembly [31,32], deployable structures [33] and anti-counterfeit applications [34][35][36][37][38][39][40], activation of the SME may not be carried out right after programming, but after a period of storage. As such, we need to consider the influence of aging at around room temperature after programming [41], which is a topic that has been less explored so far [42,43], but that is utterly important from an engineering application point of view.…”

“…It is concluded that from an engineering application point view, for this particular PMMA, programming should be done at higher temperatures (i.e., above its T g of 110 • C) in order to not only achieve reliable and better shape memory performance, but also minimize the influence of storage on the shape memory performance and mechanical behavior of the programmed material. This finding provides a useful guide for engineering applications of shape memory polymers, in particular based on the multiple-shape memory effect, temperature memory effect, and/or low temperature programming.2 of 12 applications [34][35][36][37][38][39][40], activation of the SME may not be carried out right after programming, but after a period of storage. As such, we need to consider the influence of aging at around room temperature after programming [41], which is a topic that has been less explored so far [42,43], but that is utterly important from an engineering application point of view.The purpose of this paper is to experimentally investigate the influence of storage at 40 • C on the shape memory performance and mechanical behavior of a commercial poly(methyl methacrylate) (PMMA), which is a typical engineering polymer, used in many applications, including optical lens [44,45] and plastic screw.…”

“…2 of 12 applications [34][35][36][37][38][39][40], activation of the SME may not be carried out right after programming, but after a period of storage. As such, we need to consider the influence of aging at around room temperature after programming [41], which is a topic that has been less explored so far [42,43], but that is utterly important from an engineering application point of view.…”

Shape Memory Polymer Foam with Programmable Apertures

“…Shape memory polymers (SMPs) are stimuli-responsive materials. [ 1 , 2 , 3 , 4 , 5 ] Once thermomechanically treated (programmed), they maintain a temporary shape until the shape memory effect (SME) is triggered. The activation of the so-called one-way shape memory effect (1W SME) results in the almost complete recovery of the original shape.…”

Direct‐Ink Written Shape‐Morphing Film with Rapid and Programmable Multimotion

“…However, these methods would compromise the mechanical strength of the hydrogels and lead to the buckling of the film, which restricts complex and robust deformation. In practical applications of soft actuators, like artificial muscles, sensors, soft robotics, a fast response and robust deformation are both critical. Therefore, a facile and programmable method is highly desirable to create fast response/recovery actuators with a robust structure to achieve complex deformation.…”