Controlled levitation of nanostructured thin films for sun-powered near-space flight

Abstract

We report light-driven levitation of macroscopic polymer films with nanostructured surface as candidates for long-duration near-space flight. We levitated centimeter-scale disks made of commercial 0.5-micron-thick mylar film coated with carbon nanotubes on one side. When illuminated with light intensity comparable to natural sunlight, the polymer disk heats up and interacts with incident gas molecules differently on the top and bottom sides, producing a net recoil force. We observed the levitation of 6-mm-diameter disks in a vacuum chamber at pressures between 10 and 30 Pa. Moreover, we controlled the flight of the disks using a shaped light field that optically trapped the levitating disks. Our experimentally validated theoretical model predicts that the lift forces can be many times the weight of the films, allowing payloads of up to 10 milligrams for sunlight-powered low-cost microflyers at altitudes of 50 to 100 km.

Optical manipulation and assembly of micro/nanoscale objects on solid substrates

“…With the existence of a temperature difference (Δ T ) at the object surface, the gas molecules around the high-temperature side will exert a larger force on the object than the low-temperature side, resulting in a net force toward the low-temperature side ( Shvedov et al., 2010 ). Alternatively, when one side of the object has a larger thermal accommodation coefficient than the other side, the gas molecules will leave the surface with a higher average velocity after the collision, leading to the net momentum transfer and a photophoretic force pointing to the side with a lower thermal accommodation coefficient ( Azadi et al., 2021 ). Photophoresis has been widely exploited for the manipulation of light-absorbing objects, such as carbon spheres ( Porfirev, 2019 ; Shvedov et al., 2009 ), carbon nanotube clusters ( Pan et al., 2012 ; Wang et al., 2016 ), and absorbing plates ( Cortes et al., 2020 ).…”

“… (E) Photophoretic levitation of a mylar film from the substrate. Figures reproduced from: (A and B) ( Lu et al, 2017b ) Copyright 2017, American Physical Society; (D and E) ( Azadi et al, 2021 ) Copyright 2021, American Association for the Advancement of Science. …”

“…Azadi et al. demonstrated the optical levitation of mylar thin films from a solid substrate through the photophoretic force resulting from the difference of thermal accommodation coefficients ( Azadi et al., 2021 ). Only one side of the mylar film (bottom side) was coated with a carbon nanotube layer ( Figure 1 D).…”

Elastic Recovery Properties of Ultralight Carbon Nanotube/Carboxymethyl Cellulose Composites

“…It has also been reported that ultralight aerogels with density less than air density can be levitated in air by controlling the temperature and selectively expanding the air inside the aerogel [ 22 ]. Such ultralight materials with ultimate lightness have the potential for further applications such as in communication and sky transportation [ 23 , 24 ].…”

Enhancing the Photophoretic Lift Force at Low Reynolds Numbers using Three-Dimensional Porous Structures

“…Finally, we levitated mock payloads heavier than the plates themselves (silicon pieces with milligram-scale mass). Silicon-based "smart-dust" systems with similar mass have been demonstrated to have extensive sensing, communications, and power capabilities [4,5].…”