Delamination by osmotic swelling of layered materials is generally thought to become increasingly difficult, if not impossible, with increasing layer charge density because of strong Coulomb interactions. Nevertheless, for the class of 2:1 layered silicates, very few examples of delaminating organo-vermiculites were reported in literature. We propose a mechanism for this repulsive osmotic swelling of highly charged vermiculites based on repulsive counterion translational entropy that dominates the interaction of adjacent layers above a certain threshold separation. Based on this mechanistic insight, we were able to identify several organic interlayer cations appropriate to delaminate highly charged, vermiculite-type clay minerals. These findings suggest that the osmotic swelling of highly charged organoclays is a generally applicable phenomenon rather than the odd exemption.

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Biodegradable, high‐barrier, flexible and transparent food packaging are required to replace current multilayered, metal‐ or halogen‐containing packaging that is nonrecyclable and nondegradable. An “all‐green” solution for food packaging made of a polylactic acid (PLA) foil (25 µm) furnished with a glycol chitosan‐clay nanocomposite coating (1.4 µm) is presented here that surpasses state‐of‐the‐art high‐performance materials like metallized poly(ethylene terephthalate) or poly(vinylidene chloride) even at harsh conditions (OTR = 0.17 cm3 m−2 day−1 bar−1 at 75% relative humidity). While the barrier side of the foil inhibits bacterial colonization, the uncoated PLA side assures biodegradability. Such a Janus feature in combination with the superb barrier performance renders this waterborne bio‐nanocomposite coating a valuable alternative to conventional less eco‐friendly food packaging materials.

Nature reveals a great variety of inorganic-organic composite materials exhibiting good mechanical properties, high thermal and chemical stability, and good barrier properties. One class of natural bio-nanocomposites, e.g. found in mussel shells, comprises protein matrices with layered inorganic fillers. Inspired by such natural bio-nanocomposites, the cationic recombinant spider silk protein eADF4(κ16) was processed together with the synthetic layered silicate sodium hectorite in an all-aqueous setup. Drop-casting of this bio-nanocomposite resulted in a thermally and chemically stable film reflecting a one-dimensional crystal. Surprisingly, this bio-nanocomposite coating was, though produced in an all-aqueous process, completely water insoluble. Analyzing the structural details showed a low inner free volume due to the well-oriented self-assembly/alignment of the spider silk proteins on the nanoclay surface, yielding high oxygen and water vapor barrier properties. The here demonstrated properties in combination with good biocompatibility qualify this new bio-nanocomposite to be used in packaging applications.

Flexible optoelectronic packaging is required to provide an ultrahigh barrier to oxygen under ambient conditions, meaning at a relative humidity above 50%. Many polymeric packaging materials, however, adsorb water vapor and the consequential softening is detrimental for the barrier properties. Despite its importance, systematic studies on the impact of the relative humidity (RH) on the oxygen permeability (OP) of clay nanocomposite barriers and convincing evidence for a potential hydrophobization due to compounding with nanosheets are scarce. Especially at filler contents greater than 30 vol %, as required for ultrahigh barriers, a severe confinement is imposed on interlayered polymer and thus its permeability properties are expected to be significantly modified as compared to the bulk. A systematic study of the relation between permeability and RH requires nanocomposite films that differ in filler content but at the same time are comparable with respect to aspect ratio, filler type, quality of texture, and one-dimensional crystallinity. By applying water-soluble polyvinylpyrrolidone (PVP) and ultrahigh-aspect-ratio synthetic clay (sodium fluorohectorite), we were able to prepare hybrid samples that meet these requirements for the first time. By spray coating, the components self-assemble into hybrid films of one-dimensional crystalline Bragg stacks. Two such hybrid films with filler contents of 31 and 40 vol % were fabricated. Indeed, the filler content was found to greatly affect the dependence of the oxygen permeability on RH. Comparing the performance of these two films, the OP in the 40 vol % sample was four times lower than would be expected because of the increase in filler content. To the best of our knowledge, this is the first convincing evidence for a pronounced confinement effect on the permeability.

Upcoming efficient air-borne wind energy concepts and communication technologies applying lighter-than-air platforms require high-performance barrier coatings, which concomitantly and nonselectively block permeation not only of helium but also of ozone and water vapor. Similarly, with the emergence of green hydrogen economy, lightweight barrier materials for storage and transport of this highly diffusive gas are very much sought-after, particularly in aviation technology. Here the fabrication of ultraperformance nanocomposite barrier liners by spray coating lamellar liquid crystalline dispersions of high aspect ratio (∼20 000) silicate nanosheets mixed with poly­(vinyl alcohol) on a PET substrate foil is presented. Lightweight nanocomposite liners with 50 wt % filler content are obtained showing helium and hydrogen permeabilities as low as 0.8 and 0.6 cm3 μm m–2 day–1 atm–1, respectively. This exhibits an improvement up to a factor of 4 × 103 as compared to high-barrier polymers such as ethylene vinyl alcohol copolymers. Furthermore, ozone resistance, illustrated by oxygen permeability measurements at elevated relative humidity (75% r.h.), and water vapor resistance are demonstrated. Moreover, the technically benign processing by spray coating will render this barrier technology easily transferable to real lighter-than-air technologies or irregular- and concave-shaped hydrogen tanks.

Systematic studies on the influence of crystalline vs disordered nanocomposite structures on barrier properties and water vapor sensitivity are scarce as it is difficult to switch between the two morphologies without changing other critical parameters. By combining water-soluble poly­(vinyl alcohol) (PVOH) and ultrahigh aspect ratio synthetic sodium fluorohectorite (Hec) as filler, we were able to fabricate nanocomposites from a single nematic aqueous suspension by slot die coating that, depending on the drying temperature, forms different desired morphologies. Increasing the drying temperature from 20 to 50 °C for the same formulation triggers phase segregation and disordered nanocomposites are obtained, while at room temperature, one-dimensional (1D) crystalline, intercalated hybrid Bragg Stacks form. The onset of swelling of the crystalline morphology is pushed to significantly higher relative humidity (RH). This disorder–order transition renders PVOH/Hec a promising barrier material at RH of up to 65%, which is relevant for food packaging. The oxygen permeability (OP) of the 1D crystalline PVOH/Hec is an order of magnitude lower compared to the OP of the disordered nanocomposite at this elevated RH (OP = 0.007 cm3 μm m–2 day–1 bar–1 cf. OP = 0.047 cm3 μm m–2 day–1 bar–1 at 23 °C and 65% RH).

Optical Microscopy (PLOM). DSC results reveal a competition between the nucleating effect of Hec, which was particularly important at low amounts, and the PEG confinement effect at higher filler loadings. Applying a self-nucleation protocol, the nucleation efficiency of the hectorite was shown to be up to 67%. The isothermal crystallization kinetics accelerated at low Hec contents (nucleation), went through a maximum and then decreased (confinement) as Hec content increased. Additionaly, a clear correlation between filler content and the Avrami index was obtained supporting the increase in confinement as filler loading increased.