One-step Coassembly of Nanocoatings and Effects of the Deposition Methods

Organic/inorganic hybrid nanocoatings with a nacre like structure have attracted high interest because of their outstanding properties. A one-step coassembly method has previously been developed to prepare polyvinyl alcohol (PVA)/montmorillonite (MMT) nanocoatings with a high concentration of well-aligned MMT nanosheets. To obtained these coatings, dip coating is commonly used for flow-induced orientation. In this dissertation, different coating methods are investigated to explore alternatives to overcome the deficiencies of dip coating. Spray coating is a versatile method that has virtually no limitation on substrate size or shape. Spray coating was varied through time and number of cycles. In addition, a rotational coating method was developed to apply continuous centripetal acceleration (4.0 to 48.8 m/s2) to the nanosheets while drying to decrease production time. Both methods were proven to fabricate nanocoatings with sufficient performance for various applications. While PVA is an ideal polymer binder, it is often desirable to introduce other binders with specific functionalities for new application development. As such, chitosan was selected to introduce antimicrobial properties to the nanocoatings. By introducing chitosan into the system, the resultant nanocoatings maintain a high O2 barrier, possess antimicrobial properties, and are more sustainable. Paper is a versatile material but not ideal for packaging applications due to its porous structure. As such, a method was developed to impregnate the PVA/MMT nanocoating into the pores of paper, as well as to coat the surface, to significantly improve the water vapor barrier. In addition, an impregnation method was developed to form free-standing films, which usually are hard to be delaminated from the substrate if prepared via traditional coating methods. An all-MMT inorganic film was first prepared by casting a dispersion containing well-exfoliated MMT nanosheets and then impregnated with polyvinylidene fluoride (PVDF). The impregnation of PVDF helped further align the MMT nanosheets and improve the mechanical properties of the final product. Overall, two new coating methods were developed for one-step coassembly of nanocoatings, an additional polymer binder and a new substrate were explored, and an impregnation method was developed. More importantly, this work may inspire the invention of new processing methods to prepare nacre-like structures.