Gradient functional characteristic of polymer/nanoparticle stacks on a polyethylene naphthalate film

Gradient refractive index layered antireflection (GRIL-AR) films were fabricated using a layer-by-layer (LbL) self-assembly method. As a substrate, we chose indium tin oxide-polyethylene naphthalate (ITO-PEN; the refractive index of PEN is 1.77). We deposited the GRIL-AR films on the PEN side of ITO-PEN, and the refractive index was gradually decreased from 1.59 to 1.35 by alternating deposition cycles of SiO₂ as a low-refractive-index material and TiO₂ as a high-refractive-index material. In the LbL process, each material was movable because it was coated in wet conditions; this may have led to fabrication of the gradient refractive index. When poly(ethylene imine) (PEI) was compared with poly(diallyldimethylammonium chloride), antireflection (AR) using PEI showed high abrasion durability because of the loopy structure of the polymer and a high polymer ratio in the film. With the drying process, the prepared film showed enhanced abrasion durability. GRIL-AR on ITO-PEN showed broad-band AR properties.