On the splashing threshold of droplets impinging on solid surfaces

Abstract

When a drop impinges on a dry solid surface it can stick to the surface, spread, bounce off the surface or splash. It is shown that critical conditions of splashing inception, the so-called splashing threshold, have often been obtained under slightly different experimental conditions and are partly contradictory. Furthermore, no general agreement on the basic physical mechanism causing splashing does exist. After considering those parameters that are likely to govern splashing in a dimensional analysis, limiting conditions of splashing are re-evaluated comparing the specifics of different experimental setups. Information drawn from these considerations is used to distinguish between different splashing thresholds. Existing correlations of the threshold can be divided into (at least) two groups. In addition to the roughness also the degree of dryness of the surface may be important. Finally, for smooth surfaces there is evidence that the wetting behaviour plays an important role for the inception of splashing. Based on the discussion a possible mechanism causing the onset of splashing on smooth surfaces is proposed. This mechanism may also explain the well-known fingering of the liquid lamella formed after impact.