Revealing Triple‐Shape Memory Effect by Polymer Bilayers

Abstract

Bilayer polymers that consist of two epoxy dual-shape memory polymers of well-separated glass transition temperatures have been synthesized. These bilayer epoxy samples exhibit a triple-shape memory effect (TSME) with shape fixities tailorable by changing the ratio between the two layers. The triple-shape fixities of the bilayer epoxy polymers can be explained by the balance of stress between the two layers. Based on this work, it is believed that the following three molecular design criterions should be considered in designing triple-shape memory polymers with optimum TSME: 1) well-separated thermal transitions, 2) a strong interface, and 3) an appropriate balance of moduli and relative ratios between the layers (or microphases).

Mechanisms of the Shape Memory Effect in Polymeric Materials

“…On the other hand, a few new shape memory phenomena have been discovered [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], which not only enhance the flexibility of the current shape memory technology, but also add in new dimensions for extended versatility and adoptability. Consequently, a number of novel concepts have been proposed for a range of engineering applications [45,[48][49][50][51][52][53][54], in particular in the field of biomedical engineering as of the last couple of years [24,43,[55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70].…”

“…The internal stress generated during the fabrication of the spiral spring is found to be the reason for such contraction-expansion phenomenon [102]. Another approach to achieve the multiple-SME is to have a gradient transition temperature [32,106]. In Figure 15, utilizing the influence of water on the T g of the PU (as revealed in Figure 8), by means of immersing different segments of a piece of PU wire into water for different periods of time, three different segments (top, middle and bottom) have been assigned with different T g s. Consequently, after being programmed into a "Z" shape and then immersed into room temperature water, water-induced shape recovery appears in a step by step fashion [101].…”

“…In Figure 15, utilizing the influence of water on the T g of the PU (as revealed in Figure 8), by means of immersing different segments of a piece of PU wire into water for different periods of time, three different segments (top, middle and bottom) have been assigned with different T g s. Consequently, after being programmed into a "Z" shape and then immersed into room temperature water, water-induced shape recovery appears in a step by step fashion [101]. The concept of polymeric composite, in which two or more layers of polymers with different transition temperatures, provides an alternative to achieve the multiple-SME [32]. By means of having two transition components with different transition temperatures, instead of having only one as in most of previous studies, in 2006, Professor Lendlein's group demonstrated a convenient approach to achieve the triple-SME [107].…”

Thermal Responsive Shape Memory Polymers for Biomedical Applications

“…In the case of the MACL network, the shape fixing ratio of B following deformation from C was relatively poor (R f = 48% to 87%), likely due to the fact that polymeric chains exhibiting the higher T trans and those exhibiting the lower T trans could both be affected during this delicate programming step. Using a different approach, Xie et al realized triple shape memory effect in a crosslinked macroscopic polymer bilayers with two well separated phase transitions (Xie, 2009). The bilayer SMPs were fabricated by curing an epoxy polymer layer L exhibiting a lower T g (38 °C) on top of another pre-formed epoxy polymer layer H exhibiting a higher T g (78 °C).…”

Shape memory performance of asymmetrically reinforced epoxy/carbon fibre fabric composites in flexure

“…This was, however, the topic of a polyurethane matrix composite reinforced with woven carbon fibre (CF) fabric [22]. Based also on the analogy with shape memory EP bilayers [23], developed to memorize two temporary shapes, the asymmetric reinforcement may be an interesting approach. Therefore, this work was devoted to this issue.…”