Postponed air entrainment in dilute suspension coatings



Experimental evidence is provided that the introduction of solid spheres significantly postpones the onset of air entrainment in a particular range of solid concentrations. Spherical poly(methylmethacrylate) particles were dispersed in Newtonian liquids at different weight fractions up to 1 wt %. Despite the monotonic increase in bulk liquid viscosity, the measured onset velocity of air entrainment first increased and then decreased with increasing particle number density. The maximum onset velocity was obtained at a certain particle number density that did not depend on either the particle diameter or the Bond number. A lubrication model was built by newly considering the forced air-film splitting by particle contacts. The successive consistency between the model prediction and the experimental observation suggests some directions for broadening the applicability of the coating operation to higher surface speeds. © 2005 American Institute of Chemical Engineers AIChE J, 2005