Ultrafast photomechanical transduction through thermophoretic implosion

TL;DR

This paper demonstrates a novel laser propulsion mechanism where ultrafast thermophoretic forces cause explosive bubble growth, enabling centimeter-scale manipulation of nanoparticle solutions through a thermophoretic instability.

Contribution

It introduces a new ultrafast photomechanical transduction method based on thermophoretic implosion, revealing a violent actuation of soft matter driven by laser-induced instabilities.

Findings

Nanoparticle solutions can be displaced over centimetres with laser light.

Force spikes are synchronized with sound emission and follow bubble growth.

Nanoparticles exhibit negative thermophoresis leading to explosive bubble formation.

Abstract

Since the historical experiments of Crookes, the direct manipulation of matter by light has been both a challenge and a source of scientific debate. Here we show that laser illumination allows to displace a vial of nanoparticle solution over centimetre-scale distances. Cantilever-based force measurements show that the movement is due to millisecond long force spikes, which are synchronised with a sound emission. We observe that the nanoparticles undergo negative thermophoresis, while ultrafast imaging reveals that the force spikes are followed by the explosive growth of a bubble in the solution. We propose a mechanism accounting for the propulsion based on a thermophoretic instability of the nanoparticle cloud, analogous to the Jeans instability that occurs in gravitational systems. Our experiments demonstrate a new type of laser propulsion, and a remarkably violent actuation of soft matter, reminiscent of the strategy used by certain plants to propel their spores.