This invention has applications in areas where durable anti-fog coatings are required, such as the development of optical instruments or consumer goods. In addition, the high biocompatibility of the proposed coatings also makes them well-suited to medical instruments and devices.
Poly(vinyl alcohol) (PVA) is a polymer with a wide range of biomedical applications made possible by its biocompatibility and low toxicity. Its solubility in water at physiological pH means additional processing steps are required to stabilize the polymer and improve its mechanical properties. Conventionally, PVA coatings are prepared by solvent casting the polymer onto substrates and subjecting the coating to post-treatment procedures designed to stabilize it through cross linking or crystallization. However, the solvent casting process does not allow fine-grained tuning of composition and properties in the film. This invention describes a novel layer-by-layer assembly method that results in a durable PVA conformal coating with highly tunable mechanical and chemical properties.
The anti-fog coating described in this invention is essentially a multilayer made up of alternating layers of PVA and another polymer, such as poly(acrylic acid) (PAA). The first step in depositing the coating is to covalently bond an anchoring polymer layer such as poly(glycidyl methacrylate) (PGMA) to the substrate, before depositing the first PVA layer and inducing covalent bonding between the two layers. Subsequently, alternating layers of PAA and PVA can be deposited until the desired number of layers and film thickness is attained.
Adjacent PAA and PVA layers are held together by hydrogen bonding. This means that the film can be tuned to dissolve at specific pH values by modifying the degree of hydrolysis of PVA used to assemble to coating or substituting PAA for an alternative material such as a copolymer of PAA with poly(ethylene glycol) (PAA-co-PEG) or poly(methacrylic acid) (PMAA). The multilayer can also be cross-linked by a brief heat treatment process to render it permanently insoluble.
Excellent anti-fog performance can be achieved by additionally functionalizing PAA-PVA coatings with PEG-OH or f-PEG-OH during the cross-linking process. Experiments by the inventors’ have demonstrated that anti-fog performance of the resultant coating is unaffected by cleaning with Windex.
Improved tunability compared to conventional solvent-cast coatings
Sufficiently durable to withstand cleaning with aggressive agents such as Windex
Amenable to additional surface functionalization for specific applications