Functional Nanocoatings Fabricated from Aqueous Polymer Complexes

Abstract

Layer-by-layer deposition has provided a framework in which coatings with a variety of functionality can be deposited from aqueous solutions in ambient conditions. Despite the many advantages of layer-by-layer assembly, the process requires many processing steps to deposit films of adequate thickness. The work in this dissertation focuses on using polyelectrolyte complex suspensions to deposit similar functional films more quickly and easily.

Impressive flame retardancy on cotton fabric was achieved by depositing polyethylenimine/poly(sodium phosphate) nanocoatings on cotton in a sol-gel process. By raising the pH of the suspension of the two oppositely-charged polyelectrolytes to 9.0, a stable complex was formed. After depositing these polymers onto cotton by wet-pickup, a simple treatment in acidic buffer yielded a durable, conformal film on the cotton fibers. The coating rendered the fabric self-extinguishing during vertical flame testing, as well as reduced the peak heat release rate by 88% during pyrolysis combustion flow calorimetry.

A polyelectrolyte complex coating consisting of poly(allyl amine) and poly(sodium phosphate) was deposited on polyester-cotton fabric. Not only did this nanocoating render the fabric self-extinguishing during vertical flame testing, with only 18 wt% coating, it outperformed a layer-by-layer assembled film of the same weight. This coating also showed impressive wash durability, maintaining flame retardancy after five home launderings and eight hours in boiling water.

A polyelectrolyte complex coacervate was rod coated onto PET to provide excellent oxygen barrier. After treating the coating in humidity and subsequent 150 ⁰C thermal cross-linking, the film consisting of polyethylenimine and polyacrylic acid reduced the oxygen transmission of 127 µm PET by a factor of 120.