Self-propulsion of a light-powered microscopic crystalline flapper in water

TL;DR

This paper demonstrates the first experimental realization of a light-powered microscopic crystal that self-propels in water through reciprocating motion, mimicking biological swimming behaviors and revealing the influence of crystal deformation on swimming direction.

Contribution

It introduces a novel experimental microcrystal swimmer and a mathematical model explaining how deformation affects its propulsion mechanism and directionality.

Findings

Crystals exhibit self-continuous reciprocating swimming in water.

Deformation features determine pull-type or push-type swimming modes.

Directionality is influenced by the crystal's physical deformation characteristics.

Abstract

A key goal in developing molecular microrobots that mimic real-world animal dynamic behavior is to understand better the self-continuous progressive motion resulting from collective molecular transformation. This study reports, for the first time, the experimental realization of directional swimming of a microcrystal that exhibits self-continuous reciprocating motion in a two-dimensional water tank. Although the reciprocal flip motion of the crystals was like that of a fish wagging its tail fin, many of the crystals swam in the opposite direction to which a fish would swim. Here we explore the directionality generation mechanism and physical features of the swimming behavior by constructing a mathematical model for the crystalline flapper. The results show that a tiny crystal with a less-deformable part in its flip fin exhibits a pull-type stroke swimming, while a crystal with a fin that uniformly deforms exhibits push-type kicking motion.