Wetting dynamics of a droplet impact on target-like chemically heterogeneous substrates: The determinations of contact angle

Wetting is a common natural phenomenon with many useful applications. However, some fundamental aspects of wetting theory, such as determining the contact angle, remain unresolved. Two mainstream options are debated: whether the contact angle depends on the contact area or the contact line. To understand this, the present work used many-body dissipative particle dynamics to simulate wetting on chemically heterogeneous substrates. The simulations show that there is a ratio that separates contact angles into two regimes: a stable regime where the contact angles follow the contact-area-based Cassie-Baxter equation, and a fluctuating regime where contact angles are mainly determined by the contact line. The ring/droplet ratio, initial impact velocity, and wettability pair all play a role in the formation of the contact angle. This brief communication provides clear and sound observations to shed light on the determinations of the contact angle.