Self‐Solidifying Active Droplets Showing Memory‐Induced Chirality

Abstract

Most synthetic microswimmers do not reach the autonomy of their biological counterparts in terms of energy supply and diversity of motions. Here, this work reports the first all‐aqueous droplet swimmer powered by self‐generated polyelectrolyte gradients, which shows memory‐induced chirality while self‐solidifying. An aqueous solution of surface tension–lowering polyelectrolytes self‐solidifies on the surface of acidic water, during which polyelectrolytes are gradually emitted into the surrounding water and induce linear self‐propulsion via spontaneous symmetry breaking. The low diffusion coefficient of the polyelectrolytes leads to long‐lived chemical trails which cause memory effects that drive a transition from linear to chiral motion without requiring any imposed symmetry breaking. The droplet swimmer is capable of highly efficient removal (up to 85%) of uranium from aqueous solutions within 90 min, benefiting from self‐propulsion and flow‐induced mixing. These results provide a route to fueling self‐propelled agents which can autonomously perform chiral motion and collect toxins.

Self-propulsion of a calcium alginate surfer

“…23–25 In addition to the camphor dissolution, only a recent article reports on tension-lowering polyelectrolyte reactants, which self-generate motion without an additive. 26 In a different way, the concept of exclusively one chemical reaction is responsible for the motion was also imagined earlier by van’t Hoff, by generating osmotic pressure gradient as the concept of truly exploiting “chemomechanical” forces. 27 The idea to convert chemical energy into mechanical motion in a form of an osmotic motor is supported by computational results.…”

Collective Behaviors of Isotropic Micromotors: From Assembly to Reconstruction and Motion Control under External Fields

“…To date, different reactions and external fields have been applied to generate colloid swarms (Scheme 1), including ionic/neutral species concentration gradients produced by a catalytic or noncatalytic reaction [32], thermal gradients generated by a photothermal conversion [33], and magnetic and electric fields [34,35]. These chemical reactions or external fields can affect microscopic forces among colloidal particles, such as the hydrodynamic force [36], magnetic dipolar force [37], π-π stack force [38], hydrophobic force [39], interfacial tension [40][41][42][43], etc., ultimately leading to the formation of microswarms. Unlike other micromotor swarms based on Janus particles and microtubes, the isotropic character of colloidal particles provides a model system to study the interparticle interaction and clustering mechanism in out-of-equilibrium systems, as well as contributing to larger colloidal clusters for drug delivery, resistance to external disturbance, and high efficiency imaging [44][45][46][47][48][49][50][51][52].…”