Effect of Coating Thickness on Particle Bounce in Inertial Impactors

A coating technique for applying uniform, thin layers of grease onto impactor substrates is described. The technique involves dissolving or diluting the grease in a solvent, applying the grease solution to the substrate, the spinning the substrate at a high speed. The coating thickness is controlled by the concentration of grease in the solution and by the spin speed. Apiezon-L vacuum grease and silicone oil were tested with this technique. Coating thicknesses between 0.3 and 9 μm were successfully generated on the polycarbonate film. The coated substrates and uncoated polycarbonate were tested for particle collection efficiency with polystyrene latex in two stages (0.56- and 1.0-μm cut-size) of a microorifice uniform deposit impactor. In the range of coating thicknesses tested, the collection efficiency of Apiezon-L was strongly related to the coating thickness; large coating thicknesses greatly improved particle collection. For the silicone oil, collection efficiency was high for all the coating thicknesses. The thinnest coating of silicone oil performed as well as the thickest coating of Apiezon-L grease.