Shape-Memory Composites Based on Ionic Elastomers

Abstract

Shape-memory polymers tend to present rigid behavior at ambient temperature, being unable to deform in this state. To obtain soft shape-memory elastomers, composites based on a commercial rubber crosslinked by both ionic and covalent bonds were developed, as these materials do not lose their elastomeric behavior below their transition (or activation) temperature (using ionic transition for such a purpose). The introduction of fillers, such as carbon black and multiwalled carbon nanotubes (MWCNTs), was studied and compared with the unfilled matrix. By adding contents above 10 phr of MWCNT, shape-memory properties were enhanced by 10%, achieving fixing and recovery ratios above 90% and a faster response. Moreover, by adding these fillers, the conductivity of the materials increased from ~10−11 to ~10−4 S·cm−1, allowing the possibility to activate the shape-memory effect with an electric current, based on the heating of the material by the Joule effect, achieving a fast and clean stimulus requiring only a current source of 50 V.

Review of Thermoresponsive Electroactive and Magnetoactive Shape Memory Polymer Nanocomposites

“… 39 The same work showed that the 2W-SM effect of the composite was lost when the concentration of CB was increased to 20 vol %. At the required high concentrations for resistive heating at moderate voltages (>15 wt %), this family of SMCs was reported to have lower recovery ratios, 85 more brittle behavior leading to failure of the material at shorter deformations, 86 , 87 and, in some cases, severely worsened shape fixity. 88 The last effect is found in semicrystalline SMP composites, since the addition of CBs decreases the amount of crystalline regions within the composite, 39 which are in charge of fixing the temporary shape.…”

“…It also has been shown that, at the same concentrations, CNT-filled SMCs exhibit higher shape fixity than other fillers, such as CBs, 87 which may be attributed to the alignment of the CNTs in the direction of the deformation. In the same work, the authors also showed that their shape memory elastomer filled with CNTs displays a better shape recovery ratio and better overall shape memory characteristics, as can be seen in Figure 4 .…”

“… Relationship between the shape recovery ratio and the shape fixity ratio of a SMC with different concentrations (in phr) of CBs or CNTs (reproduced with permission from ref ( 87 ); published by MDPI, 2022.) …”

Recent Developments in Shape Memory Elastomers for Biotechnology Applications

“…A category of smart materials, SMEs react to external stimuli such as temperature, pressure, electromagnetic fields, chemicals (and pH), water, light, and so on. The responsive physical properties could be stiffness, shape, and damping, among others [1,9,14,24,[40][41][42]. A recent SME was developed by Rim et al (2022) [43].…”

“…Smart materials can acquire, convey, or process a stimulus and reply by creating a 'useful' effect. This ability offers opportunities for responsive materials in applications such as actuation, shape memory, and sensing in industries including biomedicine, aerospace, textiles, and so on [8][9][10][11][12][13][14].…”