Contact Angle Mapping Using Microdroplets

Most surfaces of practical interest are heterogeneous, with natural surfaces often exhibiting microscale variations in wetting characteristics. These variations make it challenging to accurately characterize surface properties and interactions with fluids using conventional bulk contact angle measurements. Existing methods for directly measuring microcontact angles are limited by inadequate spatial resolution or reliance on indirect, force-based approaches. To address these challenges, we present a novel contact angle mapping goniometer that deposits picoliter droplets to visualize and quantify apparent contact angles and contact angle hysteresis with a spatial resolution as low as tens of microns. We validate the device on test surfaces with varying contact angles and apply it to tertiary basalt samples to investigate their wetting properties for geological carbon sequestration. We also examine Bacillus subtilis biofilms, where wettability significantly impacts antibiotic efficacy. This research advances the understanding of surface wettability and its implications across scientific and industrial applications.