Exceptional Flame Resistance and Gas Barrier with Thick Multilayer Nanobrick Wall Thin Films

Abstract

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.

Extreme Thermal Shielding Effects in Nanopaper Based on Multilayers of Aligned Clay Nanoplatelets in Cellulose Nanofiber Matrix

“…[ 2 ] However, these high temperature polymers, especially in the form of fi bers, are expensive and have substantial environmental impact in terms of high energy expenditure and carbon footprint. [ 6 ] Still, for the purpose of thicker fi lms or coatings in the 50-100 µm range, the LbL technique is in many cases impractical. [ 2,3 ] The potential of clay as a "green" nanocomponent in fi re retardant textiles has been demonstrated using thin clay-polymer coatings applied in a layer-bylayer (LbL) nanotechnology approach with closely controlled nanostructure and high clay content.…”

“…Recently, somewhat thicker (4-6 µm) fi re retardant coatings containing 82-87 wt% clay were produced by LbL and showed good performances already with less than ten bilayers when deposited on a polystyrene sheet of 3.2 mm thickness. [ 6 ] Still, for the purpose of thicker fi lms or coatings in the 50-100 µm range, the LbL technique is in many cases impractical.…”

Effect of the Biopolymer Charge and the Nanoclay Morphology on Nanocomposite Materials

“…As examples, an enhancement of the mechanical performances (Young modulus and stress at breaking) and heat resistance as well as a decrease of gas permeability and flammability were observed. 11,12,13 Due to the large surface/volume ratio of the reinforcing phase, low content of nanofillers (< 5-6 %wt) might cause a significant improvement of some physico-chemical properties. 9,10,14,15 In this work, halloysite nanotubes (HNT) and kaolinite (Kao) were used as natural nanofillers.…”

Water‐Based Assembly of Polymer–Metal Organic Framework (MOF) Functional Coatings

“…A wide variety of substrates are amenable to LbL assembly, ranging from silicon and glass to even textiles and Teflon . Materials including polyelectrolytes, nanoparticles, zeolites, metal oxides, and DNA have been successfully assembled for applications such as energy storage, membrane separations, and drug delivery . Despite the versatility of LbL assembly, it is not immediately obvious as to whether MOF particles can be assembled because of existing challenges with tailoring their dispersibility in water and surface charge.…”