The switch of behaviour of sized papers during liquid drop impaction

The impact and recoil of water drops on several flat and macroscopically smooth model surfaces and sized paper surfaces were studied over a range of drop velocities using a high speed CCD camera. The water drop impact and recoil results obtained from the model hydrophobic and hydrophilic surfaces were in agreement with observations reported previously. The maximum drop sprcading diameter at the impaction was found to be dependent upon the initial drop kinetic energy and the extent of drop recoil from the substrates after impaction was found to be much weaker for hydrophilic substrates than for hydrophobic substrates. The sized papers, however, showed an interesting switch of behavior in the event of water drop impact and recoil. The sized paper was found to behave like a hydrophobic substrate when water drop impacted on it, but like a hydrophilic substrate when water drop recoiled. Implications of this phenomenon were discussed in the context of inkjet print quality and of the surface conditions of sized papers. Atomic force microscopy was used to probe fibres on sized paper surface. The AFM data showed that water interacted quite strongly with fibre surface, even though the paper was heavily sized. Results of this study are very useful to the understanding of inkjet ink droplet impaction on paper surface which sets the initial condition for ink penetration into paper after the impaction.