Introduction to foam induced shape memory effect: non-contact loading to program shape memory polymers

The challenge to bring up new methods for programming and stimulating smart materials is an unstoppable global trend, with particularly strong momentum toward facilitating them. The external contact loading conventionally employed to induce strain (to form a temporary shape) is replaced with a non-contact loading resulting from bubbles growth during the foaming process. The obtained results confirmed that the induced internal strain during the foaming process was fully applicable to program shape memory polymer foams. It was revealed that by using this method, the significant volumetric strain (up to 80%) is attainable in the shape memory polymer foams. Executing the shape recovery process on the foam-induced shape memory polymers indicated that the higher values of the shape recovery ratios (up to 90% in the case of high volumetric strains) are achievable. Moreover, variation of programming parameters caused significant differences in volumetric strain (from 10 up to 80%) and shape recovery ratios (from 60 up to 100%). Finally, performing actuation stress measurement in different foam-induced shape memory polymers discovered that meaningful promotion (more than two times) in actuation stress is attainable as the saturation time and foaming temperature increase.