The
increased use of high-voltage electronics requires higher performance
dielectric materials. These electrically insulating layers need as
high of a dielectric breakdown strength as possible. Herein, multiple
polyelectrolyte layer-by-layer assemblies were studied as high-voltage
insulators. The influences of molecular weight, polymer backbone architecture,
and thermal cross-linking were investigated. It was found that increasing
the molecular weight of either the polycation or polyanion increases
the breakdown strength due to removal of chain ends that can act as
breakdown initiating sites. It was also found that a linear polymer
backbone architecture leads to higher breakdown strength when compared
to branched polymer architectures. Lastly, through thermal cross-linking,
the breakdown strength is increased, and the previously mentioned
molecular weight and architecture effects are diminished. These 200–400
nm thick polymer multilayer films exhibit breakdown strengths of ∼300–400
kV/mm. Their simple water-based processing makes them an interesting
new option for protecting various types of electronics.
Soft furnishing fires contribute to 29% of fire causalities and $8.7 billion in direct property damage annually in the United States. Polyurethane foam (PUF), a common component in soft furnishings known for its comfort and flexibility, can emit toxic gases and propagate fires due to melt dripping when ignited. Various acid salts were added to a layer-by-layer assembled nanocoating, consisting of chitosan and carboxymethyl cellulose, to improve PUF flame retardancy and to understand the influence of salt-doping on flammability. The 20-bilayer phosphoric acid-doped coating exhibits a self-extinguishing behavior, with a 67% reduction in peak heat release rate while maintaining the structural integrity of the foam. By depositing this completely environmentally sourced coating on PUF, the inherent danger of soft furnishing fires can be significantly reduced in a nontoxic manner.
The development of electrical insulators that are thermally conducting is critical for thermal management applications in many advanced electronics and electrical devices. Here, we synthesized polymer nanocomposite (PNC) films composed of polymers [polyethylenimine, poly(vinylamine), poly(acrylic acid), and poly(ethylene oxide)] and dielectric fillers (montmorillonite clay and hexagonal boron nitride) by layer-by-layer technique. The cross-plane thermal conductivity [Formula: see text] of the film was measured by the 3ω method. The effect of various factors such as film growth, filler type, filler volume fraction, polymer chemical structures, and temperature on the thermal conductivity is reported. The [Formula: see text] of PNCs with thickness from 37 nm to 1.34 μm was found to be in the range of 0.11 to 0.21 ± 0.02 W m−1 K−1. The [Formula: see text] values were found to be lower than the constituent polymer matrix. The experimental result is compared with existing theoretical models of nanocomposite systems to get insight into heat transfer behavior in such layered films composed of dielectrics and polymers.
Polyelectrolyte complex (PEC) thin films have demonstrated remarkable oxygen barrier properties, but the moisture sensitivity from the hydrophilic nature of polyelectrolytes is a significant drawback. In this study, various molar ratios (1:1, 1:2, and 1:3) of branched polyethyleneimine (PEI) and poly(acrylic acid) (PAA) were prepared as one‐pot coating solutions, which can be deposited via a simple dip‐coating process and cured with a citric acid buffer solution, which increases the charge density of PEI and triggers complexation. As‐prepared conformal thin films impart excellent gas barrier, high modulus, and high moisture resistance. Undetectable oxygen transmission rate (OTR), at both 0% and 90% RH, can be achieved with a PEI:PAA molar ratio of 1:1 and buffer curing at pH 3. The strong complexation from ionic crosslinking creates an unusually dense thin film that is promising for various packaging applications (food, electronics, etc.). This thin film exhibits one of the best‐ever polymer‐based oxygen barriers at high humidity.
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