In an effort to develop a more environmentally benign flame retardant for polyurethane foam (PUF), layers of halloysite clay nanotubes (HNT) stabilized by branched polyethylenimine (BPEI) or poly(acrylic acid) (PAA) are deposited from aqueous suspensions to create multilayered nanocomposite coatings. PUF is very flammable and widely used in upholstered furniture throughout the world. Foam treated with five BPEI-HNT/PAA-HNT bilayers, deposited using layer-by-layer assembly, is rendered self-extinguishing in open flame testing. Cone calorimetry reveals that this coating reduces the peak heat release rate (pkHRR) by 62%. Due to the tubular morphology of HNT, small volatile gasses given off during combustion are trapped, so total smoke release (TSR) is reduced by 60%. Infrared spectroscopy suggests this multilayer film survives during combustion, forming an HNT-rich barrier that prevents mass and energy transfer during open flame testing and calorimetry. The significant reductions in pkHRR and TSR, along with the self-extinguishing behavior, indicate that these halloysite-based multilayer films have the potential to greatly improve PUF fire safety. The low cost and natural abundance of HNT makes this technology especially amenable to widespread use.

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Single-crystal SnSe 2 nanosheets with a ten atomic-layer thickness have been prepared by a facile solvothermal route reaction in benzyl alcohol in the presence of PVP. Benzyl alcohol acts as the solvent and reducing reagent to promote the formation of the hexagonal phase of SnSe 2 , and the presence of PVP provides a stable environment for the construction of the SnSe 2 nanosheets. A reasonable formation mechanism was put forward on the basis of the time-dependent experiments. The obtained SnSe 2 nanosheets displayed an enhanced photocurrent compared to the thick SnSe 2 nanoplates, which indicated potential applications in photodetectors, photovoltaic devices and so forth.

In an effort to produce effective thermoelectric nanocomposites with multiwalled carbon nanotubes (MWCNT), layer-by-layer assembly was combined with electrochemical polymerization to create synergy that would produce a high power factor. Nanolayers of MWCNT stabilized with poly(diallyldimethylammonium chloride) or sodium deoxycholate were alternately deposited from water. Poly(3,4-ethylene dioxythiophene) [PEDOT] was then synthesized electrochemically by using this MWCNT-based multilayer thin film as the working electrode. Microscopic images show a homogeneous distribution of PEDOT around the MWCNT. The electrical resistance, conductivity (σ) and Seebeck coefficient (S) were measured before and after the PEDOT polymerization. A 30 bilayer MWCNT film (<1 μm thick) infused with PEDOT is shown to achieve a power factor (PF = Sσ) of 155 μW/m K, which is the highest value ever reported for a completely organic MWCNT-based material and competitive with lead telluride at room temperature. The ability of this MWCNT-PEDOT film to generate power was demonstrated with a cylindrical thermoelectric generator that produced 5.5 μW with a 30 K temperature differential. This unique nanocomposite, prepared from water with relatively inexpensive ingredients, should open up new opportunities to recycle waste heat in portable/wearable electronics and other applications where low weight and mechanical flexibility are needed.

Hydrogen-bonded multilayer thin films are very stretchable, but their gas barrier properties are modest compared to more traditional ionically bonded assemblies. In an effort to improve the gas barrier of poly(ethylene oxide) (PEO)-poly(acrylic acid) (PAA) multilayer films without sacrificing stretchability, montmorillonite (MMT) clay platelets were combined with PAA and alternately deposited with PEO. A ten-bilayer PEO/PAA+MMT film (432 nm thick), deposited on a 1 mm PU substrate, resulted in a 54× reduction in oxygen transmission rate after exposure to a 20% strain. This system is the best combination of stretchability and gas barrier ever reported.

of their colloidal stability, mechanical strength, high specific surface area, and thermal stability, [2][3][4][5][6] which have been used to produce transparent paper, biodegradable packaging, complex aerogels, and as the reinforcing phase in composites. [2,4,7,8] Despite all of its beneficial properties, cellulose exhibits poor flame resistance and gas barrier properties. [9,10] Improved barrier, mechanical, and flame resistant properties have been reported when montmorillonite clay (MMT) is used as a reinforcing agent in cellulose-based films. [11][12][13] The performance of polymer-clay barrier films is determined primarily by the clay characteristics (e.g., aspect ratio and density) and dispersion properties (i.e., clay exfoliation and orientation). For cellulose/clay composites, different methods to increase the interaction between clay and cellulose have been reported, including TEMPO-oxidation and by adding poly(vinyl alcohol) or chitosan (CH) as a compatibilizer. [14][15][16] Recently, cationic CNF with a quaternary ammonium functionality has been reported. [17] It was shown that the ionic interaction between the cationic CNF and MMT results in better mechanical properties of the composite, but further improvement is limited due to the formation of nanovoids as well as relatively low clay loading. [12,18] Layer-by-layer (LbL) assembly is a nanocoating technique that has been used to construct functional thin films for gas barrier and gas separation coatings, [19,20] energy storage and conversion, [21,22] drug delivery, [23] and adhesives. [24] By alternately depositing oppositely charged polyelectrolytes and/or clay platelets onto a charged substrate, thin films are assembled with high clay concentration and alignment. [25] In the present study, multilayer films consisting of anionic vermiculite (VMT) clay, with a high aspect ratio (≈2000), and cationic cellulose nanofibrils were investigated. This unique combination of highly aligned VMT platelets and cellulose nanofibrils forms a nanobrick wall structure with high transparency, excellent oxygen barrier, and fire resistance (superior to any other cellulose-based film previously reported). A 20 bilayer (BL) CNF/VMT nanocoating, with a thickness of 136 nm, exhibits a low oxygen transmission rate (OTR) of 0.013 cc (m 2 day atm) -1 . With only 2 BL of CNF/VMT, the melting of flexible polyurethane (PU) foam is prevented when exposed to a butane torch flame. These nanocoatings also exhibit high elastic modulus Cellulose nanofibrils (CNF) are abundant in the fiber cell walls of many plants and are considered a nearly inexhaustible resource. With the goal of improving the flame resistance and gas barrier properties of cellulose-based films, cationic CNF are assembled with anionic vermiculite (VMT) clay using the layer-by-layer deposition process. The highly aligned VMT nanoplatelets, together with cellulose nanofibrils, form a nanobrick wall structure that exhibits high optical transparency, flame resistance, super oxygen barrier, and high modulus. A 20 CNF/VMT...

A thin film coating with tailorable thickness and clay concentration was prepared by solution casting an aqueous slurry containing poly(vinyl alcohol) (PVOH) and montmorillonite (MMT) clay. The anisotropic clay platelets have excellent alignment due to self-orientation during drying, which results in good transparency and oxygen barrier. A 50 wt % clay coating, with a thickness around 4 μm and visible light transmission of 58%, improves the oxygen barrier of a 179 μm poly(ethylene terephthalate) (PET) substrate by more than 3 orders of magnitude. This PVOH/MMT composite thin film also has good thermal stability and mechanical properties. This simple coating procedure could be used for a variety of packaging applications that use plastic film (e.g., food, pharmaceutical, and electronics).

Nanoindentation and nanoscratch experiments were performed on thin multilayer films manufactured using the layer-by-layer (LbL) assembly technique. These films are known to exhibit high gas barrier, but little is known about their durability, which is an important feature for various packaging applications (e.g., food and electronics). Films were prepared from bilayer and quadlayer sequences, with varying thickness and composition. In an effort to evaluate multilayer thin film surface and mechanical properties, and their resistance to failure and wear, a comprehensive range of experiments were conducted: low and high load indentation, low and high load scratch. Some of the thin films were found to have exceptional mechanical behavior and exhibit excellent scratch resistance. Specifically, nanobrick wall structures, comprising montmorillonite (MMT) clay and polyethylenimine (PEI) bilayers, are the most durable coatings. PEI/MMT films exhibit high hardness, large elastic modulus, high elastic recovery, low friction, low scratch depth, and a smooth surface. When combined with the low oxygen permeability and high optical transmission of these thin films, these excellent mechanical properties make them good candidates for hard coating surface-sensitive substrates, where polymers are required to sustain long-term surface aesthetics and quality.