Experimental procedure for achieving multi-graded foams by gas foaming with time-varying boundary conditions

We show that, by ingeniously designing the sorption step, it is possible to achieve non-trivial gas concentration profiles and, correspondingly, at pressure release, foams with density and/or morphology profiles. As a model system, we foamed polystyrene with CO2 and N2, and achieved three- as well as five-layered foams, gradually or sharply graded, yet in a single foaming step (pressure release) executed after different sorption protocols.