The impact dynamics of droplets of different liquids onto solid surfaces with different roughness was investigated by using the high-speed microphotography. The influences of viscosity
surface tension and surface roughness on the non-dimensional maximum spreading diameter and the critical Weber number for transition from spreading to splashing were discussed. The results showed that the non-dimensional maximum spreading diameter decreases with the increasing liquid viscosity
and higher surface tension makes droplet more possible to retract after impacting on the solid surface. It was also observed that water is the only liquid that retracts in the experiment since it has obviously higher surface tension than other three liquids. The droplet needs to wet larger surface and will have higher viscous dissipation with the increase of surface roughness
leading to the decrease of the maximum spreading diameter at the same Weber number. The relationship of the maximum spreading diameter with Weber number
Ohnesorge number and surface roughness was obtained by introducing surface roughness to Laan's equation. The “finger-like” disturbance around the rim becomes more obvious with the increase of surface roughness
which makes the droplet more likely to splash after impact onto the solid surface and leads to lower critical Weber number for transition from spreading to splashing. In addition
the surface roughness influences the critical Weber number more significantly for the liquids with smaller Ohnesorge number.
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references
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