FOIM: From foam to foil and back again

Shape memory polymers (SMPs) are smart materials that perform a shape change in response to an external stimulus, usually a temperature change, after being thermomechanically treated. This thermomechanical process is referred to as “programming” and involves heating the SMP above the phase transition temperature of the switching segments (glass or melting transition temperature), loading, cooling below the phase transition temperature (glass or crystallization transition temperature) and unloading. The SMP retains the programmed shape until it is heated above the transition temperature again, which triggers the one-way shape memory effect and the material returns to its original shape.
The current study presents the semi-finished product FOIM (cf. Figure 1), a polyester urea urethane foam with a hard/soft segment ratio of 1.06 and an open pore content of 78 %. As determined by differential scanning calorimetry, the foam exhibited a melting peak at around 45 °C and a crystallization peak at 14 °C. When subjected to significant compressive deformation at 60 °C and afterwards cooling to room temperature, upon programming, the foam transformed into a translucent foil that remained stable at room temperature. When reheated to 60 °C, the foil turned back into foam recovering 99.5% of its original height. Notably, the structure remained largely unaffected by the deformation, as evidenced by buoyancy and heat transmission measurements. The ease of manufacture and functionality of this technology make it attractive for applications that require both a smaller transport volume and significant shape changes.
References:
[1] T. Pretsch in Smart Materials (Ed.: H. Böse), Vogel Communications Group, Würzburg, 2023, pp. 227–259.
[2] L. Santo, Progress in Aerospace Sciences 2016, 81, 60-65.
[3] A.-L. Poser, T. Pretsch; “FOIM: Thermal Foaming of Shape Memory Polyurethane Foil”, manuscript submitted for publication.