Enhanced Coffee-Ring Effect via Substrate Roughness in Evaporation of Colloidal Droplets

Figure 6

Formation mechanism of evaporation patterns on (a–d) a smooth substrate and (e–h) a rough substrate. (a) On a smooth substrate, the contact angle is larger and the evaporation rate is low; (b) recycling flow is constructed on the smooth substrate; (c) in the later stages of evaporation, many particles remain in the dispersion on the smooth substrate; (d) wedge-shaped cross-section of the deposition; (e) on a rough substrate, the contact angle decreases and the wicking effect emerges, leading to a higher evaporation rate; (f) there is no circumfluence on the rough substrate, with contact angle hysteresis being more evident; (g) almost no particles remain in the center; (h) high-shaped cross-section morphology.