Light-switchable deposits from evaporating drops containing motile microalgae

TL;DR

This study demonstrates how light can be used to control the pattern formation of deposits from evaporating drops containing motile microalgae, enabling precise manipulation of coffee ring structures.

Contribution

It introduces a novel method to manipulate deposit patterns by leveraging the light-sensitive motility of microalgae during evaporation.

Findings

Light wavelength and angle influence deposit patterns.

Motile microalgae can resist and alter typical coffee ring effects.

Light control enables pattern suppression and direction.

Abstract

Deposits from evaporating drops have shown to take a variety of shapes, depending on the physicochemical properties of both solute and solvent. Classically, the evaporation of drops of colloidal suspensions leads to the so-called coffee ring effect, caused by radially outward flows. Here we investigate deposits from evaporating drops containing living motile microalgae (Chlamydomonas reinhardtii), which are capable of resisting these flows. We show that utilizing their light-sensitivity allows to control the final pattern: adjusting the wavelength and incident angle of the light source enables to force the formation, completely suppress and even direct the spatial structure of algal coffee rings.