Improving the Gas Barrier Property of Clay–Polymer Multilayer Thin Films Using Shorter Deposition Times

Abstract

Relatively fast exposure times (5 s) to aqueous solutions were found to improve the gas barrier of clay-polymer thin films prepared using layer-by-layer (LbL) assembly. Contrary to the common belief about deposition time (i.e., the longer the better), oxygen transmission rates (OTRs) of these nano-brick-wall assemblies are improved by reducing exposure time (from 1 min to 5 s). Regardless of composition, LbL films fabricated using shorter deposition time are always thicker in the first few layers, which correspond to greater clay spacing and lower OTR. A quadlayer (QL) assembly consisting of three repeat units of branched polyethylenimine (PEI), poly(acrylic acid) (PAA), PEI and montmorillonite (MMT) clay is only 24 nm thick when deposited with 1 min exposure to each ingredient. Reducing the exposure time of polyelectrolytes to 5 s not only increases this film thickness to 55 nm but also reduces the oxygen transmission rate (OTR) to 0.05 cm3/(m2 day atm), which is 2 orders of magnitude lower than the same film made using 1 min exposures. A conceptual model is proposed to explain the differences in growth and barrier, which are linked to polyelectrolyte relaxation, desorption, and interdiffusion. The universality of these findings is further exemplified by depositing clays with varying aspect ratios. This ability to quickly deposit high-barrier nanocomposite thin films opens up a tremendous opportunity in terms of commercial-scale processing of LbL assemblies.

Gas barrier properties of polymer/clay nanocomposites

“…5,40 The incorporation of clay platelets into polymers initially attracted attention because of improvements in mechanical properties of polymer. 33,37,[56][57][58][59][60][61][62][63][64][65][66][67][68][69] The most widely used clay ller for the enhancement of gas barrier property of PNCs is MMT as it has large cation exchange capacity. 33,37,[56][57][58][59][60][61][62][63][64][65][66][67][68][69] The most widely used clay ller for the enhancement of gas barrier property of PNCs is MMT as it has large cation exchange capacity.…”

“…Then LDPE/O-MMT nanocomposites was prepared by twinscrew extruder and hot-press. 25,26,58,59,[64][65][66]76,101,104,[147][148][149][150]171,172 By alternating exposure of a substrate to components with complementary interactions (Fig. 132 PET is one of the most widely used polymers in the packaging industry.…”

“…132 PET is one of the most widely used polymers in the packaging industry. 58 The polymer/clay nanocomposites thin lms prepared by LbL assembly were found to exhibit extremely low OTR, high transparency in the visible light spectrum and tunable gas barrier behavior. Sanchez-Garcia et al prepared PET/O-MMT nanocomposites by melt process in an internal mixer.…”

Gas barrier properties of bio-inspired Laponite–LC polymer hybrid films

“…The PLA/MMT films consisting of 5 wt% clay reported by Thellen et al [42] exhibited a reduction in the oxygen permeation rate of up to 48% compared to the reference PLA films. In comparison with polyelectrolyte/ MMT films, films consisting of polyelectrolytes and Laponite platelets, which have a much lower aspect ratio than MMT platelets, were found to exhibit much higher oxygen transmission rates [43]. In contrast, high loadings of large aspect ratio vermiculite potentially reduce the oxygen transmission by many orders of magnitude [37].…”

Boron nitride nanosheets as barrier enhancing fillers in melt processed composites

“…In fact mechanical measurements (see SI, figure S3) show the composite stiffness to increase with volume fraction up to φ~0.02, after which the modulus falls. 70,71 We also calculated the diffusivity via a "half-time" method, which is a modification of the conventional time-lag technique and suitable for the measurement at atmospheric pressure. For example, previous mechanical measurements on BNNS/polymer composites were consistent with an aggregation threshold of 0.15 vol%.…”