Micrometre-sized Droplet Contact Line Advancement on Micropillared Surfaces

Understanding microscale droplet behaviour on structured surfaces is essential for designing and developing applications that require precise wetting control, like condensation, biomedical diagnostics, and inkjet printing.

Traditional wettability characterisation methods (droplet goniometry, tilting plate) are limited to droplets with sizes several orders of magnitude greater than the structural features or which distort the droplet shape, reducing measurement accuracy. While condensation introduces uncontrolled nucleation and coalescence, which complicates the analysis of contact line behaviour.

To overcome this limitation, we use microgoniometry to investigate the impact of circular micropillars on the dynamics of advancing contact lines of micrometre-sized droplets. Experimental results on micropillared surfaces with varying interpillar spacing reveal that the ratio of droplet size to pillar spacing and the overall pillar density significantly influence contact line advancement and jump behaviour. Micropillars induce stick-jump behaviour that becomes more distinct but less frequent as spacing increases, while the average advancing contact angle decreases.

Our research enhances the understanding of the relationship between microstructure design and droplet wetting behaviour at comparable length scales, providing insights for optimising surface engineering in scientific and industrial contexts.