Transient High-energy Surface Powered By A Chemical Fuel

A common practice to regulate surface energy(γ)depends on stimuli-responsive surfactants that switch between active and inactive forms;this equilibrium-based strategy is,however,binary in origin and difficult to regulate in the time domain.Here,we leverage nonequilibrium chemistry to construct an aqueous system that can be transiently excited to a high-energy state by a chemical fuel before relaxation to a ground state.Specifically,this system embodies three elements—a surfactant to change γ,a fuel(cyclodextrin)to deactivate the surfactant,and a fuel burner(amylase)to enzymatically consume the fuel—that are mutually dependent as governed by an equilibriumreaction coupling.Three fundamental processes are at play: the adsorption equilibrium between bulk and adsorbed surfactant molecules,the host-guest equilibrium between CD and surfactant molecules,and the enzymatic reaction that consumes CD.Specifically,fuel injection quickly lifts a system from the ground to high-energy states(low to high γ)and fuel consumption then reverts the system to the ground state over time;a parametric space is mapped out to finely tune the excitation-relaxation in terms of base/excitation levels and half-life.Continuous supply of fuel at different rates provides us a full control over the temporal profile,realizing for example stable intermediate states over a prolonged period.At the very heart of this strategy is their proper coupling and we derive a theoretical model to account for it.In full consistency with experimental data,this model can quantitatively describe the dependence of excitation-relaxation behavior on varies initial conditions,and it further guides us to precisely shape the temporal profile into arbitrary forms(such as staircases or sinusoidal waves,highlighting a remarkable predictive power)by programing time-dependent fuel influx.A semiautomatic workflow is established to convert a targeted function of surface tension into realistic,experimental measurement.Practically,the current system operates at a mild condition(～ 20 to90 °C and p H ～ 4 to 8 for a good enzymatic activity)on a reasonable time scale(mins to one hour);it consists of simple synthetic chemicals and a commercially available enzyme;it is insusceptible to waste accumulation because the waste,glucose,is water-soluble and surface-inactive.Finally,we demonstrate its applications in wetting,capillarity,and weight support,and we expect its ease adaptability in a wide range of surface/interface-involved scenarios such as emulsification,foaming,and liquid transportation.