On the role of liquid viscosity in affecting droplet spreading on a smooth solid surface

Abstract The role of liquid viscosity on droplet spreading behavior upon impacting on a smooth stainless steel surface has been experimentally investigated. Results show the droplet spreading dynamics with increasing viscosity (characterized by the Ohnesorge number, Oh ) exhibits complex dependence on the impact inertia (characterized by Weber number, We ). Specifically, for a small impact inertia ( We H a . The non-dimensional maximum diameter β max first increases and then decreases with increasing Oh , and this non-monotonic phenomenon has not been reported previously. For an intermediate impact inertia (60 We β max , and it has the form of a rim-bounded lamella. Although β max shows a monotonic decrease with increasing Oh ,  some unsmooth disturbance around the rim occurs only at intermediate Oh . For a higher impact inertia ( We >240), droplet splashing emerges and then vanishes with increasing Oh , although β max still decreases monotonically. All the observed phenomena imply that liquid viscosity may have a dual role in affecting the droplet spreading, which previous models of β max do not take into account.