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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 (k ⊥) 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 k ⊥ 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 k ⊥ 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. [ABSTRACT FROM AUTHOR]

Flax fabric textile is of great interest as bio‐fiber reinforcement in composites, which has gained popularity due to the high demand for sustainable materials. Despite its sustainability, flax is inherently flammable. This study demonstrates a two‐step polyelectrolyte complex (PEC) coating that renders flax fabric self‐extinguishing. The PEC coating consists of polyethylenimine (PEI) and sodium hexametaphosphate (PSP), cured with a citric acid buffer. Sonication employed during the curing process improves the infiltration of the coating into the flax fibers and maintains the fabric's hand. When comparing non‐sonicated and sonicated flax samples, the latter achieves self‐extinguishing behavior and passes the vertical flame test. Pyrolysis‐combustion flow calorimetry reveals that this PEI/PSP coating (with sonication) reduces the peak heat release rate and total heat release by 40% and 67%, respectively. The intumescent mechanism is predominantly observed in the condensed phase, as suggested by differential scanning calorimetry and X‐ray photoelectron spectroscopy. The results demonstrate that the two‐step PEC treatment with sonication effectively reduces the flammability of flax fabric, making it a promising option for the development of functional fibers, particularly for bio‐composite reinforcement. [ABSTRACT FROM AUTHOR]

Dielectric materials that can withstand high voltages are of great interest due to the growing need for high‐performance insulation systems in electronics. Polymer nanocomposites have gained popularity as electrical insulators due to their processability, high operating voltage, and tortuous paths for current flow created by the nanoparticles in the polymer matrix. The dielectric breakdown strength of a relatively thick multilayer thin film containing polyethylenimine (PEI) and vermiculite clay (VMT), thickened with tris(hydroxymethyl)aminomethane (tris), is evaluated as a function of bilayers (BL) deposited. The resulting nanobrick wall structure of this clay‐based assembly is ideal for protective insulation. An 8 BL PEI+tris/VMT film achieves a dielectric breakdown strength of 245 kV mm−1, with a thickness of 5 µm. With increasing bilayers, the breakdown strength gradually decreases, but 20 BL of PEI+tris/VMT achieves a breakdown voltage of 2.36 kV. This nanoplatelet‐based system is the first "thick growing" layer‐by‐layer deposited film to be used as an insulating layer. Its unusually high breakdown strength can be useful for the protection of various high voltage electronics. [ABSTRACT FROM AUTHOR]

Nylon–cotton blended fabric (NYCO), commonly used in military uniforms and workwear for its comfort and resilience, presents an inherent fire risk due to its high flammability and high heat release. There are few effective flame retardant treatments for NYCO that are environmentally benign and maintain the hand of the fabric. To solve this problem, a layer‐by‐layer (LbL)‐assembled 15 quadlayer (QL) coating, consisting of chitosan (CH), phytic acid (PA), and tannic acid (TA), is applied to NYCO. Individually pairing TA or PA with CH is not self‐extinguishing, but they work synergistically in the QL system to create an effective intumescent coating. This completely bio‐sourced, water‐based coating self‐extinguishes in a vertical flame test (ASTM D6413), with only 16.6% weight added to NYCO, yielding 91% postburn residue and a 51% decrease in peak heat release rate. This novel coating provides an opportunity to replace environmentally questionable flame retardant treatments with a fully sustainable system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]