Stability of Polymer Coatings on Nebulizer Membranes During Aerosol Generation

The dimensions of orifices found in aperture plates used for nebulization can be modified by thin polymer coatings with the aim to control the size distribution of the generated aerosol droplets. However, the stability of such polymer coatings on the surface of nebulizer membranes during aerosol generation has not been elucidated. Nebulizer membranes made of stainless steel were covered with a thin film of poly(chloro-p-xylylene) (~1 μm) in the presence or absence of a silane-based adhesion promoter. Thereby, the orifice cross-sections of the nebulizer membrane were reduced by ~50%, accompanied by a remarkable decline in droplet size. Upon continuous nebulization of aqueous test liquids, the droplet size generated by the nonconditioned (no silane), poly(chloro-p-xylylene)-coated membranes reverted to that of the uncoated nebulizer membrane within ~5 min. By contrast, no such rapid return of droplet size to "baseline" values was noticed for the silane-conditioned, poly(chloro-p-xylylene)-coated counterparts. Scanning electron microscopy exhibited significant polymer detachment from the orifices of the nonconditioned (no silane) membranes and thus confirmed the findings from laser diffraction. Overall, silane-based adhesion promoters can increase the persistence of poly(chloro-p-xylylene) coatings on nebulizer membranes during aerosol generation.