Switching Propulsion Mechanisms of Tubular Catalytic Micromotors

Different propulsion mechanisms have been suggested for describing the motion of a variety of chemical micromotors, which have attracted great attention in the last decades due to their high efficiency and thrust force, enabling several applications in the fields of environmental remediation and biomedicine. Bubble‐recoil based motion, in particular, has been modeled by three different phenomena: capillary forces, bubble growth, and bubble expulsion. However, these models have been suggested independently based on a single influencing factor (i.e., viscosity), limiting the understanding of the overall micromotor performance. Therefore, the combined effect of medium viscosity, surface tension, and fuel concentration is analyzed on the micromotor swimming ability, and the dominant propulsion mechanisms that describe its motion more accurately are identified. Using statistically relevant experimental data, a holistic theoretical model is proposed for bubble‐propelled tubular catalytic micromotors that includes all three above‐mentioned phenomena and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions. A new holistic theoretical model implying the switching and coexistence of propulsion mechanisms for conical catalytic micromotors is proposed. The model combines the already reported mechanisms based on capillary forces, bubble growth, and bubble expulsion phenomena in one single approach, allowing for an adequate description of the experimentally detected micromotor dynamics.