Effect of surface roughness on the collision dynamics of water drops on wood

[Display omitted] The impingement of water drops on Diospyros crassiflora and Handroanthus spp. wood substrates, with roughness ranging from 0.50 to 5.7 μm, were investigated. The results indicated that surface roughness controlled (i) the mobility of the liquid film, (ii) the integrity of the impinging drop, and (iii) the energy balance during the drop impact process. More specifically, the decreased mobility of the liquid film (at increased roughness) was evident from the more irregular lamella, prominent finger projections, and a decreased spreading. An increased roughness was characterized by violent splashing of impinging water drops, localized rupturing of liquid film, and highly fragmented splats. The greater likelihood of an impinging water drop exhibiting recoil on rougher wood surfaces implied a reduced contact between the liquid film and the wood surface; subsequently resulting in a stronger influence of capillary force that drives the recoil. On very rough Diospyros crassiflora substrates, however, the absence of recoil and more intact splats pointed towards the impalement of the drop within the wood surface. Interestingly, the absence of such phenomena on very rough Handroanthus spp. substrates delineated the possibility that drop impact behavior on wood was also influenced by additional factors, such as the physicochemical properties of wood.