Layer‐by‐layer (LbL) assembly is a powerful and versatile technique to deposit functional thin films, but often requires a large number of deposition steps to achieve a film thick enough to provide a ...desired property. By incorporating amine salts into the cationic polyelectrolyte and its associated rinse, LbL clay‐containing nanocomposite films can achieve much greater thickness (>1 μm) with relatively few deposition cycles (≤6 bilayers). Amine salts interact with nanoclays, causing nanoplatelets to deposit in stacks rather than as individual platelets. This technique appears to be universal, exhibiting thick growth with multiple types of nanoclay, including montmorillonite and vermiculite (VMT), and a variety of amine salts (e.g., hexylamine and diethanolamine). The characteristic order found in LbL‐assembled films is maintained despite the incredible thickness. Films assembled in this manner achieve oxygen transmission rates below 0.009 cc m−2 d−1 atm−1 with just 6 bilayers (BLs) of chitosan/VMT deposited. These thick clay‐based thin films also impart exceptional flame resistance. A 2‐BL film renders a 3.2 mm polystyrene plate self‐extinguishing, while an 8‐BL film (3.9 μm thick) prevents ignition entirely. This ability to generate much thicker clay‐based multilayers with amine salts opens up tremendous potential for these nanocoatings in real world applications.
The incorporation of amine salts is shown to generate relatively thick clay nanocomposites via layer‐by‐layer assembly. These relatively thick nanofilms display extraordinary gas impermeability and flame resistance. A 6‐bilayer (BL) polymer/clay film has an oxygen permeability equivalent to SiOx thin films, while an 8‐BL film prevents ignition of a thick polystyrene plate entirely in a flame‐through test.
Multilayer thin films of graphene oxide (GO) and poly(vinylamine) (PVAm) were deposited via layer-by-layer assembly. Poly(vinylamine) pH was used to tailor film thickness and GO layer spacing. ...Graphene oxide concentration in the films was controlled through simple pH adjustment. Thermal reduction of the PVAm/GO multilayer thin films rendered them electrically conductive, which could be further tailored with PVAm pH. These reduced films also exhibited exceptionally high elastic modulus of 30 GPa and hardness of 1.8 GPa, which are among the highest of any graphene-filled polymer composite values ever reported. Cross-linking of these films with glutaraldehyde improved their chemical resistance, allowing them to survive strongly acidic or salty solutions. Additionally, scratches in the films can be instantaneously detected by a simple electrical resistance measurement. These films are promising for a variety of packaging and electronic applications.
Here, we report template‐assisted assembly of emissive carbon quantum dot (CQD) microcrystals on organized cellulose nanocrystals templates at the liquid–air interface. This large‐scale assembly is ...facilitated by the complementary amphiphilic character of CQDs and cellulose nanocrystals in the organized nematic phase. The resulting large microcrystals up to 200 μm across show unusually high emission that is not observed for limited CQDs aggregates. The dense crystal packing of CQDs in the layered fashion suppresses local molecular rotations and vibrations, thus restricting the intermolecular energy transfer and corresponding quenching phenomena. The as‐prepared crystals are mechanically stable and can be exploited for recyclable catalysis, enabling applications beyond the individual nanoparticles or disordered aggregates. The ligand‐templated assembly can be used to diversify CQD crystal architectures to guide formation of fibers, microplates, and micro‐flowers.
The template‐assisted assembly of large and emissive carbon quantum dot (CQD) microcrystals using organized amphiphilic cellulose nanocrystals (CNCs) at the liquid–air interface is presented. This large‐scale assembly is facilitated by the complementary amphiphilic interactions of CQDs and CNCs in an organized nematic phase.
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