Instabilities of ring-rivulets: Impact of substrate wettability.

Rivulets and droplets are naturally appearing shapes when small amounts of liquid are deposited on a partially wettable substrate. Here, we study, by means of numerical simulations, the dewetting dynamics of a ring-rivulet on substrates with various contact angles and wettability patterns. In particular, we consider, beyond the homogeneous case, an annular band of lower contact angle compared to the background and a constant radial gradient of contact angle, pointing either inward or outward from the center. We show that by tuning the parameters characterizing the patterns, it is possible to control not only the stability of the rivulet, i.e., its breakup/collapse dynamics and the associated time scales, but also the dewetting morphology, in terms of the number and position of the formed droplets.