Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism

Abstract

We demonstrate the new features of a polyurethane shape memory polymer: water-driven actuation and recovery in sequence (i.e., programmable). Hydrogen bonding is identified as the reason behind these features. In addition, the absorbed water is quantitatively separated into two parts, namely, the free water and bound water. Their individual contribution on the glass transition temperature is identified.

Mechanisms of the Shape Memory Effect in Polymeric Materials

“…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]. 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].…”

“…Since the plasticizing effect is able to effectively reduce the T g , instead of heating over T g to trigger the thermally induced SME, to reduce the T g of a polymer to below room temperature by means of exposing to the right chemical for the plasticizing effect is an alternative for shape recovery [14,[97][98][99][100]. Such a chemo-responsive SME is generic and applicable to all three working mechanisms presented in Figure 5.…”

Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers

“…In general, the polymer's shape memory (SM) effect is described and evaluated in a thermo-temporal SM cycle, where the SMP is firstly deformed at a high temperature (usually above the glass transition or melting point) and subsequently frozen upon cooling to fix the programmed temporary shape. When an environmental stimulus is applied, the SMP could either provide recovery stresses or return to their permanent shapes, depending on whether or not the external loads still exist, namely the constrained or free recovery condition [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] . Since SMPs can sense the environmental changes and then take reactions in a predetermined sequence with deformation, they are considered as a promising alternative for the future's spontaneous shape changing and tunable components in various applications such as microelectromechanical systems, surface patterning, biomedical devices, aerospace deployable structures and morphing structures [31][32][33][34][35][36][37][38][39] .…”

Comment on “Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism” [Appl. Phys. Lett. 86, 114105 (2005)]

“…Phys. Lett We would like to thank Huang et al 1 for their insightful and helpful research on "Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism." The authors demonstrated that shape recovery actuation of polyurethane shape memory polymer ͑SMP͒ can be achieved by water.…”