Abstract
A centimeter-sized flat-headed push pin with photothermal properties can be moved on a water surface by a simple near-infrared laser. Using light as an external stimulus allows for the remote control of the timing, direction and velocity of its locomotion. It has been clarified that the vertical orientation of the pin at the air–water interface affects the friction of locomotion, and therefore velocity and acceleration. The pin placed on a water surface with a pin point upward (a point protruding into air phase) moved an average distance of 5.3 ± 2.9 cm following one pulse of laser irradiation, and that placed with a pin point downward (a point protruding into water phase) moved 2.0 ± 1.4 cm. The velocity and acceleration were larger when the pin was placed on the water surface with a pin pointing upward, compared to when placed with the pin pointing downward. Numerical analysis conducted for the locomotions of the pin concluded that the differences in traveling distance, velocity and acceleration were due to the difference in fluid resistance of the pin point in air and water phases during their locomotion. This demonstration of remote control of the motion of small objects by light can open up a wide range of future transport applications.
Highlights
Powering and controlling the locomotion of micrometer- to centimeter-sized small objects is a fascinating research topic[1,2,3,4] with possible applications in drug delivery and micro uidics
X-ray photoelectron spectroscopy studies con rmed that the surface Cl/N atomic ratio was measured to be 0.14, which was lower than that determined for PPy bulk powder synthesized using FeCl3$6H2O in the absence of C8F (0.22)[26] (Fig. S1†)
This result strongly indicated that the PPy was doped with C8F carrying sulfonate group, and it can be expected that the per uoroalkyl group exists at the surface of the PPy
Summary
Powering and controlling the locomotion of micrometer- to centimeter-sized small objects is a fascinating research topic[1,2,3,4] with possible applications in drug delivery and micro uidics. Thanks to the PPy powder coating, the pin with hydrophobic surface can be placed on the planar air–water interface and light-to-heat photothermal property could be introduced to the pin.
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