Layer-by-layer assembled transparent polymeric adhesive films with adjustable refractive indices

Materials with high adhesive strength that can be fabricated by environmentally friendly methods are crucial for various bonding applications. In this study, highly adhesive films with an adjustable refractive index (RI) were prepared by the layer-by-layer (LbL) assembly of cationic poly(diallyldimethylammonium chloride) (PDDA) and an anionic blend of poly(acrylic acid) (PAA) and poly(4-styrenesulfonic acid) (PSS). The RI of the adhesive films can be precisely controlled between 1.5181 and 1.5562 by simply changing the PSS content. We obtained high adhesive strengths in the range 3.99 +/- 1.04 MPa to 6.88 +/- 0.95 MPa by gently pressing two glass substrates together with transparent (PDDA/PAA-PSS)*n LbL assembled films with different NaCl contents in the presence of a thin layer of deionized water (n refers to the number of film deposition cycles). Importantly, the water is an environmentally friendly solvent in the bonding and debonding processes. Finally, these adhesive films exhibit high optical transparency in the visible region and exhibit excellent thermal stability. The outstanding features of these films ensure their use in practical optical bonding applications.