Origin of Surface Dynamical Instability

While the silicone polymer phase provides a high enough oxygen permeability, it also dominates the surface characteristics, i.e., the surface of silicone hydrogel is too hydrophobic to be used as a contact lens. The silicone phase also readily absorbs 

Because the hydrophilic polymer with negative charge in aqueous solution would not adhere to the silicone phase on the first dipping operation, it is likely that hydrophobic islands remain as the coating thickness increases with a repeated, 

The results indicate that Sudan black penetrated into the bulk phase of lens. The dye permeation test of LBL-coated lens in wet conditions did not show stain. However, when a thin layer of liquid water exists on the surface, the dye test losses validity in terms of evaluating the barrier property of the coating because the oil spreads on the water layer, which acts as a barrier to oil-soluble dye. Wet uncoated lens did show the dye stain, which probably indicates that water on uncoated lens is not as strongly held by the surface as LBL-coated surface. The dye permeation test of LBL-coated lenses under blotted and dried conditions showed stain. The stain in blotted sample was spotty and the color intensity is less than that for the dried surface, which is more intense than that for uncoated lens, i.e., dried LBL-coated lens has the strongest dye absorption. 

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