Contactless Manipulation of Binary Droplets via Sensing of Localized Vapor Sources

TL;DR

This paper introduces a novel contactless method for manipulating binary droplets on pristine surfaces by sensing localized vapor sources, enabling precise control without specialized substrates or wettability gradients.

Contribution

The study presents a new vapor-sensing technique for long-range, contactless droplet manipulation, expanding capabilities beyond traditional wettability gradient methods.

Findings

Demonstrated contactless manipulation of binary droplets using vapor sensing.

Validated the mechanism through analytical modeling of surface tension asymmetries.

Achieved controlled printing, alignment, and reaction of materials in space and time.

Abstract

Droplet motion on surfaces influences phenomena as diverse as microfluidic liquid handling, printing technology and micro-organism migration. Typically, droplet motion is achieved by inducing energy gradients on a substrate or flow on the droplet's free surface. Current configurations for droplet manipulation have, however, limited applicability as they rely on carefully tailored wettability gradients and/or bespoke substrates. Here we demonstrate the contactless long-range manipulation of binary droplets on pristine substrates due to the sensing of localized water vapor sources. We show with analytical considerations that the dissipative nature of the driving forces at play, induced by tiny asymmetries in surface tension gradients, is essential to capture the droplet's manipulation mechanism. We then demonstrate its versatility by printing, aligning and reacting materials controllably in space and time.