Influence of polymer interdiffusion and clay concentration on gas barrier of polyelectrolyte/clay nanobrick wall quadlayer assemblies
Thin film assemblies of polyvinylamine (PVAm), branched polyethylenimine (PEI), poly(acrylic acid) (PAA) and sodium montmorillonite (MMT) clay created by layer-by-layer technique were used to study the influence of interdiffusion and clay concentration on oxygen permeability. The quadlayer (QL) film assemblies grown by switching polycation layers from PVAm to PEI were found to have difference not only in thickness, but the degree of ionization. It is believed that PEI was able to facilitate PAA to ionize and induce interdiffusion more compare to PVAm. The layer-by-layer assembly coated on 179 μm poly(ethylene terephthalate) (PET) showed a visible light transmission decreased only 2% as the thickness increased ten times, indicating that clay platelets were packed parallel to the PET film. Atomic force and transmission electron microscope images also reveal the fact that MMT are highly oriented, creating an extended gas diffusion pathway that will extremely reduce oxygen transmission rate (OTR). While coated on PET film, a 6QL PVAm assembly with only 175nm thick presented an OTR of 0.009 cm3/ (m2*day*atm). The OTR was found to be related to both the degree of interdiffusion and clay concentration in the LbL film, hence desired barrier properties can simply be obtained by switching PVAm layers to PEI. This study demonstrates a promising alternative in polymer/clay composite films to be used in flexible electronic barriers and food packaging.
Tzeng, P; Maupin, CR; Grunlan, JC; J. Membr. Sci., 2014, 452 (13), 46-53.