Chemically Fueled Autonomous Sol→Gel→Sol→Gel→Sol Transitions.

Complex non-equilibrium phase behaviors are a hallmark of natural self-assembling systems. Here we show how intricate phase transitions can be achieved through a chemically fueled reaction cycle to yield autonomous sol→gel→sol→gel→sol transitions. A relay of chemical transformations based on thiazinane metathesis leads to two consecutive transient gelations in a closed system. Within seconds of fuel addition to deactivated thiazinane monomers, an imine-based hydrogel forms that consists of fibrillar microspheres. This gel quickly loses its mechanical strength and forms a solution, from which a second aldehyde-based gel nucleates and remains stable for over one day. Overall, our reaction cycle gives rise to two consecutive re-entrant phase transitions without any experimental intervention.