"The most significant aspect of this work is that these antireflection coatings are conformally applied from water solutions," Michael Rubner of Massachusetts Institute of Technology told nanotechweb.org. "Hence they can be used to coat many different types of materials, including plastics - which can be problematic when high-temperature processes and harsh solvents are required."

The researchers made the films by applying an aqueous treatment to multilayers of poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA). By carefully controlling the pH during the process, they gave the films a nanoporous structure. With further treatment, pores could be removed or reintroduced.

"The fact that we can reversibly open and close the pores is significant from the standpoint of membrane and drug-delivery applications," explained Rubner.

According to Rubner, the nanoporous films could provide cheap, easily tunable broadband antireflection coatings for a variety of plastic optical materials and lenses. Now, he says that, as well as further studying the antireflection performance of the films, the team will explore the film's applications in the areas of biomaterials and membranes.

The scientists reported their work in Nature Materials.