To grate a liquid into tiny droplets by its impact on a hydrophobic micro-grid

TL;DR

This paper investigates how impacting a liquid on a hydrophobic micro-grid can produce micro-droplets, proposing a method for controlled droplet generation and analyzing the impact threshold discrepancies.

Contribution

It introduces a novel technique to generate mono-disperse micro-droplets from a liquid drop using a hydrophobic micro-grid, with insights into impact thresholds.

Findings

Micro-droplets of about grid hole size are produced above a certain impact speed.

A method for creating mono-disperse sprays or single tiny droplets is demonstrated.

Discrepancies between measured and predicted impact thresholds are discussed.

Abstract

We report on experiments of drop impacting a hydrophobic micro-grid, of typical spacing a few tens of $\mu$m. Above a threshold in impact speed, liquid emerges to the other side, forming micro-droplets of size about that of the grid holes. We propose a method to produce either a mono-disperse spray or a single tiny droplet of volume as small as a few picoliters corresponding to a volume division of the liquid drop by a factor of up to 10$^5$. We also discuss the discrepancy of the measured thresholds with that predicted by a balance between inertia and capillarity.