Recent advances in shape–memory polymers: Structure, mechanism, functionality, modeling and applications

Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding

A review of stimuli-responsive shape memory polymer composites

Origami can turn a sheet of paper into complex three-dimensional shapes, and similar folding techniques can produce structures and mechanisms. To demonstrate the application of these techniques to the fabrication of machines, we developed a crawling robot that folds itself. The robot starts as a flat sheet with embedded electronics, and transforms autonomously into a functional machine. To accomplish this, we developed shape-memory composites that fold themselves along embedded hinges. We used these composites to recreate fundamental folded patterns, derived from computational origami, that can be extrapolated to a wide range of geometries and mechanisms. This origami-inspired robot can fold itself in 4 minutes and walk away without human intervention, demonstrating the potential both for complex self-folding machines and autonomous, self-controlled assembly.

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A method for building self-folding machines

As a new class of smart materials, shape memory polymers and their composites (SMPs and SMPCs) can respond to specific external stimulus and remember the original shape. There are many types of stimulus methods to actuate the deformation of SMPs and SMPCs, of which the thermal- and electro-responsive components and structures are common. In this review, the general mechanism of SMPs and SMPCs are first introduced, the stimulus methods are then discussed to demonstrate the shape recovery effect, and finally, the applications of SMPs and SMPCs that are reinforced with fiber materials in aerospace are reviewed. SMPC hinges and booms are discussed in the part on components; the booms can be divided again into foldable SMPC truss booms, coilable SMPC truss booms and storable tubular extendible member (STEM) booms. In terms of SMPC structures, the solar array and deployable panel, reflector antenna and morphing wing are introduced in detail. Considering the factors of weight, recovery force and shock effect, SMPCs are expected to have great potential applications in aerospace.

https://iopscience.iop.org/article/10.1088/0964-1726/23/2/023001/pdf

Shape memory polymers and their composites in aerospace applications: a review

We report a new phenomenon in which the reversible formation and disruption of a cellulose nano-whisker (CNW) percolation network in an elastomeric thermoplastic polyurethane (TPU) matrix leads to an unprecedentedly rapidly switchable shape-memory effect (SME) that may be activated by water The materials have been fully characterized to investigate the SME phenomenon using a number of different experimental techniques including cyclic tensile deformation, dynamic mechanical analysis, FTIR and polarized Raman spectroscopy A model is developed in which it is shown that exposure to water allows breakup of the CNW percolation network so that the flexible elastomer matrix can be deformed to the desired shape The CNW percolation network reforms after drying to provide a fixing force for the temporary shape The entropy elasticity of the TPU matrix then enables rapid shape recovery when the CNW percolation network is disrupted again during wetting This completely athermal water-sensitive SME mechanism is totally different from traditional ones, in which the water or other solvents are used as plasticizers to lower the glass transition temperature of shape memory polymers, so as to allow triggering of the shape recovery at room temperature or lower The reported work provides a novel and effective strategy to achieve rapidly switchable shape recovery in a material by a simple wetting process and fixing through an easily applicable programmed drying process

Rapidly switchable water-sensitive shape-memory cellulose/elastomer nano-composites

Polymeric Shape Memory Nanocomposites with Heterogeneous Twin Switches

Tunable shape recovery of polymeric nano-composites

To investigate the morphology, crystallization properties of reversible phase and thermal sensitive shape memory properties of CW/SMPU (Cellulose Whisker/Shape Memory Polyurethane) nano-composite, the CW/SMPU nano-composite having CW contents of 0.1–3.8 wt % were prepared. SEM investigation showed the evolution of reversible phase morphology from spherolite crystallization structure to uniform matrix with tiny CW aggregates with the addition of CW into the SMPU matrix. DSC and isothermal crystallization kinetic method revealed the effect of CW on crystallization properties of reversible phase and fixed phase, suggesting that the effect of CW on the crystallization of hard segment phase is not comparable with thermal history; the more CW causes the higher crystallization rate of reversible phase; the crystallization mechanism of reversible phase in nano-composite gradually evolves to heterogeneous nucleation and crystal growth in two dimensions with the increase of CW content; the excellent nucleation effect of CW for the reversible phase leads to the drop of activity energy from 134.1 kJ/mol (N-0), to 95.1 kJ/mol (N-4). Cyclic tensile tests illustrate the addition of CW content can engender rapid shape fixity ability after a relative short cooling time; the shape fixity ratio of nano-composite and the control sample after sufficient cooling all can be identically high. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Morphology, reversible phase crystallization, and thermal sensitive shape memory effect of cellulose whisker/SMPU nano-composites

Shape memory effect (SME) was achieved for cellulose–polyurethane (PU) blends of different compositions in wet–dry cycles, featuring that the amorphous cellulose and the PU content served as the fixing phase and the recovery phase, respectively. The dependence on the compositions of the fixity ratio and the recovery ratio was quantitatively measured by tensile tests. The morphological and thermal properties of the blends were further investigated by scanning electron microscopy and thermogravimetric analysis. The storage modulus of the blends varied reversibly in the wet–dry cycles, as determined by dynamic mechanical analysis. Furthermore, the microstructure of the blends reversibly changed correspondingly, as determined by wide-angle X-ray scattering diffraction and Fourier transform infrared. It was predicted that the reversible transition in different amorphous cellulose structures triggered by water led to the reversible variation in modulus as well as the wet–dry SME of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Hongsheng Luo

Papers

Rapidly switchable water-sensitive shape-memory cellulose/elastomer nano-composites

Polymeric Shape Memory Nanocomposites with Heterogeneous Twin Switches

Tunable shape recovery of polymeric nano-composites

Morphology, reversible phase crystallization, and thermal sensitive shape memory effect of cellulose whisker/SMPU nano-composites

Achieving shape memory: Reversible behaviors of cellulose-PU blends in wet-dry cycles