Scheduled System Maintenance on May 29th, 2015:
IEEE Xplore will be upgraded between 11:00 AM and 10:00 PM EDT. During this time there may be intermittent impact on performance. We apologize for any inconvenience.
By Topic

back to article  |  Figures
All Figures

Propulsion Mechanism of Catalytic Microjet Engines

Figure 1

Figure 1
Tuning the shape of rolled-up tubes. Optical microscope images of rolled-up tubes illustrating the tuneability of the shape of the tube. (a) Cylindrical tube. (b) Truncated conical tube. (c) Conical tube. Scale bar 10 μm.

Figure 2

Figure 2
Optical microscope image illustrating an actively moving Fe/Pt catalytic microjet engine (6 nm Fe and 1 nm Pt) in aqueous solutions at 1% H2O2 and 1% SDS. Scale bar 25 μm. The dashed (orange online) lines highlight the walls of the rolled-up tube.

Figure 3

Figure 3
Generation of an O2 bubble inside of the tube in an aqueous solution of 1% H2O2 and 1% SDS. (a) Aqueous solution fills the microtube from the small opening. (b) Inner surface of Pt catalyzes the decomposition of H2O2 fuel, and consequently, the generation of an O2 bubble. (c) Bubble growth and movement to the larger opening of the tube. (d) Bubble is released. The dashed (orange online) lines highlight the walls of the rolled-up tube. The red arrow shows the evolution of one single bubble inside of the tube. Scale bar 10 μm.

Figure 4

Figure 4
Scheme of a conical microjet. Geometric parameters of a spherical bubble (pink online area) touching the wall of the tube. Area with triangular crosshatching (green online) [with square crosshatching (blue online)] represents the fluid in the tube to the left (right) from the bubble.

Figure 5

Figure 5
Scheme of a bubble (blue online at time Formula$t_{0}$ and pink online at a larger time t > t0) confined to a conical tube (black). Shift of the central plane drawn at a half-height of the conical part of the bubble Formula$X_{0} \to X$ is represented by a heavy black arrow. (The contact angle θ in the scheme is exaggerated as compared to its real values.) The geometrical conditions that the conical part of the bubble is completely touching the internal wall of tube, X − h/2 ≥ 0 and X + h/2 ≤ L, are obeyed in the calculations below.

Figure 6

Figure 6
Surface tension energy Formula$E_{\rm ST}$ [short dashed (red solid online) lines] and the capillary force Formula$F_{\rm cap}$ [solid (black solid online) lines] for a bubble as a function of the position of a bubble in two microjets with (a) and (b) lower and (c) and (d) higher degree of conicity at two values of the parameter Formula$r_{c}$: (a) and (c) 3.25 μm and (b) and (d) 4.00 μm. (The shape of the tubes is represented schematically in the insets with the geometric parameters.) Long dashed (blue dashed online) lines, which are drawn through the minima of Formula$E_{\rm ST}$ as a function of Formula$X$, separate the regions, where the bubble is deformed due to the confinement to the conical tube as shown in Fig. 5 (at lager values of Formula$X$), from the regions of the spherical bubble (at smaller values of Formula$X$). In the inset to panel (c), the function Formula$E_{\rm ST}$Formula$(X)$ is represented significantly magnified near to the position of its minimum, the decaying part is represented with a dashed (red dashed online) line. In all cases, Formula$\theta$ = 24° and Formula$L$ = 50 μm.

Figure 7

Figure 7
Motion of a growing bubble under the influence of the capillary force. (a) Coordinate (b) Velocity. Position of the nucleation point of the bubble is shown in the inset; Formula$R_{\rm max}$ = 3.5 nm, Formula$R_{\rm min}$ = 3.0 nm.

Figure 8

Figure 8
(a) Jet force acting on the tube due to the motion of the growing bubble represented in Fig. 7(a). (b) Average tube velocity developed due to the jet force represented in panel (a). Position of the nucleation point of the bubble is shown in the inset.