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.
Paper-based food packaging is lightweight, low cost, and highly flexible, but it suffers from a very high oxygen transmission rate (OTR ∼ 11,100,000 cc/(m 2 •day•atm)). Herein, two polyelectrolyte-based coacervate coatings were studied as oxygen gas barriers on kraft builder's paper. A single coating deposition of a polyethylenimine-poly(acrylic acid) coacervate, adding less than 20% to the paper's weight, reduced the OTR to 164,000 cc/(m 2 • day•atm). This work not only demonstrates a significant OTR improvement of a poor oxygen barrier material, but also provides the foundation for polyelectrolyte-based layers to be deposited on cellulosic materials at an industrial scale.
Bacterial adhesion is a major concern in the medical field, where bacterial fouling can lead to diminished device efficacy and failure. To combat this, polyelectrolyte complexes (PECs) can be used to modify surfaces to reduce bacterial attachment. In the present study, a water-based PEC of poly(diallyldimethylammonium chloride) [PDDA] and poly(acrylic acid) are deposited in a simple two-step process to the surface of polyester fabric. This process includes the deposition of a dissolved mixture of the two polyelectrolytes, followed by the formation of the ionic network through exposure to citric acid buffer. These coatings facilitate the removal of >95% of deposited Staphylococcus aureus after simple rinsing with deionized water. The high degree of surface ionization monitored by FTIR suggests that electrostatic repulsion is responsible for the observed antifouling activity. The morphology of these coatings which is monitored by scanning electron microscope (SEM) and atomic force microscope (AFM) is shown to depend on curing the curing conditions, which suggests that this simple process can be tailored to many applications.
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.
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