Continuously Variable Regulation of the Speed of Bubble‐Propelled Janus Microcapsule Motors Based on Salt‐Responsive Polyelectrolyte Brushes

Abstract

The engineering of self‐propelled micro‐/nanomotors (MNMs) with continuously variable speeds, akin to macroscopic automobiles equipped with a continuously variable transmission, is still a huge challenge. Herein, after grafting with salt‐responsive poly[2‐(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes, bubble‐propelled Janus microcapsule motors with polyelectrolyte multilayers exhibited adjustable speeds when the type and concentration of the counterion was changed. Reversible switching between low‐ and high‐speed states was achieved by modulating the PMETAC brushes between hydrophobic and hydrophilic configurations by ion exchange with ClO4− and polyphosphate anions. This continuously variable regulation enabled control of the speed in an accurate and predictable manner and an autonomous response to the local chemical environment. This study suggests that the integration of polymer brushes with precisely adjustable responsiveness offers a promising route for motion control of smart MNMs that act like their counterparts in living systems.

Reversible Speed Regulation of Self‐Propelled Janus Micromotors via Thermoresponsive Bottle‐Brush Polymers

“…However, precise movement manipulations, like the control over the velocity and the direction, while particularly desirable, are still limited [4] . Simple velocity control has been reported, for example, by chemical manipulation of systems that poison the catalyst, reducing its effectiveness, [5] or by ion exchange blocking access of the fuel [6] . Alternative systems use local pH [7] or photochemical irradiation to control the speed of propulsion [8] .…”

“…[4] Simple velocity control has been reported, for example, by chemical manipulation of systems that poison the catalyst, reducingi ts effectiveness, [5] or by ion exchange blocking access of the fuel. [6] Alternative systems use local pH [7] or photochemical irradiation to control the speed of propulsion. [8] In arecent example, supramolecular stomatocyte nanomotorsd ecoratedw ith poly(N-isopropyl acrylamide) (PNIPAM) could be directed throught emperature variations.…”

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

“…Engineering self-propelled motors having a controllable speed can be of interest for many applications. For example, it was suggested to use bubble propulsion to move Janus polyelectrolyte particles [78]. Janus microcapsules were formed by grafting polyelectrolyte salt-responsive brushes onto preformed (poly(styrene sulfonate) PSS/(polyallylamine hydrochloride) PAH) 4 microcapsule protected from one side.…”

Dynamic Behaviour in Microcompartments

“…Furthermore, control of the speed of the microcompartment was realised by introducing salt‐responsive PMETAC brush growth on the Pt cap. The brush changed the wettability by inducing counter‐ion exchange, leading to a difference in the diffusion rate of H 2 O 2 , which limited the generation rate of O 2 bubbles . Similarly, instead of the non‐biocompatible Pt/H 2 O 2 system, reaction systems of urease/urea and lipase/triglyceride were also employed to power the Janus or stochastically modified mesoporous silica microparticles…”