Transient Colloid Assembly by Fuel-Driven Modulation of Depletion Interactions

In biology, energy stored in chemical fuels is used to drive processes energetically uphill, enabling the highly dynamic behavior of living organisms. The out-of-equilibrium behavior can propagate from molecular reaction networks to the micro- and macroscopic scale. These natural phenomena have sparked the design of man-made out of equilibrium chemical reaction networks (CRNs) and dissipative assembly systems with hydrogels, (supra)polymers, vesicles/micelles and colloids. In colloidal systems, the assembly process is typically controlled by balancing the interaction forces. Here, we use a polymeric depletant integrated in a fuel driven esterification CRN to induce transient colloidal assembly. The polymer undergoes a temporal coil-globule transition upon acetylation by the chemical fuel. In the random coil conformation it acts as depletant agent for the silica colloids, promoting colloidal aggregation. As compact globule, the polymer loses its
depletant characteristics. During the fuel cycle the polymer cyclically transitions from one form to the other, directly influencing colloidal aggregation and redispersion. Thus, a fuel-driven CRN on the molecular scale results in a microscopic response with a transient colloidal depletion cycle. Overall, the time-dependent propagation of out-of-equilibrium activity across length scales presented here, offers opportunities to design responsive materials with life like properties.