Improving the engine power of a catalytic Janus-sphere micromotor by roughening its surface

Abstract

<div> <div> <div> <p>Microspheres with catalytic caps have become a popular model system for studying self- propelled colloids. Existing experimental studies involve predominantly “smooth” particle surfaces. In this study we determine the effect of irregular surface deformations on the propulsive mechanism with a particular focus on speed. The particle surfaces were deformed prior to depositing a catalytic layer which resulted in the formation of nanoscopic pillars of catalyst. These features were shown to boost speed (~2×) when the underlying surface deformations are small (nanoscale), whilst large deformations afforded little difference despite a substantial apparent catalytic surface area. Colloids with deformed surfaces were more likely to display a mixture of rotational and translational propulsion than their “smooth” counterparts. </p> </div> </div> </div>

ZnO/ZnO2/Pt Janus Micromotors Propulsion Mode Changes with Size and Interface Structure: Enhanced Nitroaromatic Explosives Degradation under Visible Light

“…The enhanced motion upon increasing H 2 O 2 concentration, which was suggested based on the diffusiophoresis mechanism, is more efficient for mesoporous Janus particles when compared to solid particles. 21,22 To see the effect of porosity on diffusiophoresis motion, we have assessed the motion behavior of solid and nonporous ZnO/Pt particles, wherein the primary ZnO particles were obtained by heat treatment of 1.5 μm mesoporous particles at 1000 °C; see Figure S1 in the Supporting Information. The scanning electron micrscopy (SEM) images showed that the size of particles reduced to ca.…”

“…This finding is in accordance with other Pt-coated Janus micromotors based on silica and PS with tuned surface porosity and sizes around 1 μm. 22,31 To understand the underlying bubble-propulsion mechanism of mesoporous and hierarchical ZnO/Pt Janus micromotors, the nano/microstructures of these micromotors with sizes of ca. 5 μm were assessed by SEM coupled with EDS, as shown in Figure 3 a−c.…”

“…1 The mechanisms responsible for the motion are reported to be high-speed bubble propulsion and low-speed diffusiophoresis depending on size and surface porosity of the micromotors. 1,21,22 Other Janus micromotors based on Mg are able to reduce pure water and generate hydrogen bubbles without using any H 2 O 2 . 23 The other face of Janus micromotors could act as cargo for drug delivery or cleaning agents for water-purification approaches.…”

“…However, it should be noted that the speed of mesoporous Janus micromotors does not always increase with surface area enhancement. Longbottom and Bon 22 showed that a large deformation on smooth PS/Pt Janus particles, which resulted in a severe surface porosity, slightly reduced the final speed. Only a slight and controlled surface roughening on the smooth PS/Pt particles enhanced their propulsion speed by >3 times.…”

“…Only a slight and controlled surface roughening on the smooth PS/Pt particles enhanced their propulsion speed by >3 times. It was reported that the high surface porosity and large cavities could reduce the slip velocity around the micromotors, 21,22 and it is therefore required to design mesoporous and hierarchical micromotors with optimal surface porosity and enhanced speed.…”