Photophoretic Levitation of Macroscopic Nanocardboard Plates

Abstract

Scaling down miniature rotorcraft and flapping-wing flyers to sub-centimeter dimensions is challenging due to complex electronics requirements, manufacturing limitations, and the increase in viscous damping at low Reynolds numbers. Photophoresis, or light-driven fluid flow, was previously used to levitate solid particles without any moving parts but only at the scale of 1-20 micrometers. Here, we leverage stiff architectured plates with 50-nm thickness to realize photophoretic levitation at the millimeter to centimeter scales. Instead of creating lift through conventional rotors or wings, our levitation occurs due to light-induced thermal transpiration through micro-channels within our plates. At atmospheric pressure, the plates hover above a solid substrate at heights of ~0.5 mm by creating an air cushion beneath the plate. Moreover, at reduced pressures (10-1000 Pa), the increased speed of thermal transpiration through the plate's channels creates an air jet that enables mid-air levitation and allows the plates to carry small payloads heavier than the plates themselves. This new propulsion mechanism for macroscopic structures creates the prospect of future nanotechnology-enabled flying vehicles without any moving parts in the Earth's upper atmosphere and at the surface of other planets.