Influence of layer-by-layer deposition techniques and incorporation of layered double hydroxides (LDH) on the morphology and gas barrier properties of polyelectrolytes multilayer thin films

Abstract

The spin-spray layer-by-layer (SS-LBL) deposition technique was utilized to produce multilayer films of poly(acrylic acid) (PAA)/poly(ethylene imine) (PEI) with and without nanoparticles of layered double hydroxides (LDH), and the structure and gas barrier properties of the films were compared with those produced by the dipping layer-by-layer technique (dipping-LBL). The thickness growth of dipping-LBL films is clearly exponential, whereas the SS-LBL films exhibited a lower growth rate. Microscopy analysis revealed that the roughness is much lower, and the orientation and planarization of the LDH nanoplatelets is higher, in SS-LBL films than in dipping-LBL films. LBL films deposited on PET substrates resulted in large reductions in the gas permeabilities compared with neat PET, and this barrier effect is more intense for films deposited by SS-LBL containing LDH nanoparticles. For these films, oxygen and carbon dioxide gas permeation reductions of about 10× and 50×, respectively, were observed after only 5 deposition cycles of the sequence (PEI/PAA/LDH/PAA). Besides the higher efficiency of SS-LBL in decreasing the gas permeability, this deposition technique is also 20 times faster than dipping-LBL, and the coated films have higher light transmittance. This combination of high gas barrier, fast assembly, and high optical clarity of polymer/LDH composite nanocoatings is expected to be very attractive in the production of films for food packaging and electronic encapsulation applications.