Influence of polymer interdiffusion and clay concentration on gas barrier of polyelectrolyte/clay nanobrick wall quadlayer assemblies

Abstract

Thin film assemblies of polyvinylamine (PVAm), branched polyethylenimine (PEI), poly(acrylic acid) (PAA) and sodium montmorillonite (MMT) clay, created using the layer-by-layer assembly technique, demonstrate the influence of polymer interdiffusion and clay concentration on oxygen barrier behavior. These quadlayer (QL) assemblies can be switched from linear to exponential growth by varying the placement of PVAm and PEI layers. PEI has a much lower Tg and is better able to interdiffuse with PAA, resulting in exponential growth and greater clay deposition in each layer. When deposited on 179μm poly(ethylene terephthalate) (PET), these ‘nanobrick wall’ thin films only decreased visible light transmission by 2% as the thickness increased by a factor of 10, indicating that clay platelets are highly oriented and well separated. Atomic force and transmission electron microscope images also reveal this high level of clay orientation that creates an extended gas diffusion pathway that dramatically reduces oxygen transmission rate (OTR). A 6QL PVAm-based assembly, with a thickness of 175nm, has an OTR of 0.009cm3/(m2dayatm). OTR was found to be linked to both the degree of polymer interaction and clay concentration in these thin films. The desired barrier can be obtained by substituting PVAm layers for PEI. This study demonstrates a promising technique for tailoring the gas barrier of polymer/clay composite thin films that could find use in flexible electronics and food packaging.