The dielectric properties and loss tangents of low-density polyimide aerogels have been characterized at various frequencies. Relative constants as low 1.16 were measured for made from 2,2′-dimethylbenzidine (DMBZ) biphenyl 3,3′,4,4′-tetracarbozylic dianhydride (BPDA) cross-linked with 1,3,5-triaminophenoxybenzene (TAB). This formulation was used the substrate to fabricate test prototype microstrip patch antennas benchmark against state practice commercial antenna substrates. aerogel...

Silica aerogels are sol−gel-derived materials consisting of interconnected nanoparticle building blocks that form an open and highly porous three-dimensional silica network. Flexible aerogel films could have wide applications in various thermal insulation systems. However, thin produced with a pure sol−gel process inherent disadvantages, such as high fragility moisture sensitivity, hinder wider these materials. We developed synthesis manufacturing methods to incorporate electrospun...

The effect of incorporating an organic linking group, 1,6-bis(trimethoxysilyl)hexane (BTMSH), into the underlying silica structure a styrene cross-linked aerogel is examined. Vinyltrimethoxysilane (VTMS) used to provide reactive site on backbone for polymerization. Replacement up 88 mol % silicon from tetramethoxyorthosilicate with derived BTMSH and VTMS during making gels improves elastic behavior in some formulations aerogels, as evidenced by measurement recovered length after compression...

We report here the fabrication of polyamide aerogels composed poly-p-phenylene-terephthalamide, same backbone chemistry as DuPont's Kevlar. The all-para-substituted polymers gel without use cross-linker and maintain their shape during processing-an improvement over meta-substituted cross-linked reported previously. Solutions containing calcium chloride (CaCl2) para-phenylenediamine (pPDA) in N-methylpyrrolidinone (NMP) at low temperature are reacted with terephthaloyl (TPC). Polymerization...

A family of polyimide (PI)-based aerogels is produced using Desmodur N3300A, an inexpensive triisocyanate, as the cross-linker. The are prepared by cross-linking amine end-capped oligomers with triisocyanate. formulated 2,2'-dimethylbenzidine, 4,4'-oxydianiline, or mixtures both diamines, combined 3,3',4,4'-biphenyltetracarboxylic dianhydride, and chemically imidized at room temperature. Depending on backbone chemistry, chain length, polymer concentration, density ranged from 0.06 to 0.14...

Reinforcing silica aerogels by conformally coating the nanoskeleton with a polymer has been demonstrated to be an effective way improve mechanical properties. In addition, mesoporosity and low thermal conductivity is maintained, making this robust form of aerogel enabling material for variety aerospace applications. However, process can quite long, involving production gel, solvent exchanges, diffusion monomer, followed more exchanges supercritical fluid extraction. This paper first time...

Cellulose nanocrystals derived from tunicates (t-CNC) were used as a reinforcing nanofiller for polyimide aerogels. Two sets of aerogels, containing either 2,2′-dimethylbenzidine (DMBZ) or 4,4′-oxydianiline (ODA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) cross-linked with 1,3,5-tris(4-aminophenoxy)benzene (TAB), studied. Total solids composition the aerogels kept constant at 7.5 wt %, 0–13.33 % total being carboxylic acid-functionalized t-CNC (t-CNC–COOH) filler. The...

Polyimide aerogels have gained much attention in the last decade due to their highly porous structure with low density, dielectric constant, good mechanical properties, and thermal stability. They are desirable for many aerospace commercial applications including lightweight substrates antennas vehicles, approaching one as density decreases. However, only aromatic diamines backbone, flexible very thin films, nominally 0.5 mm thick. A more aerogel substrate would allow them be used conformal...

Silica aerogels are comprised of highly porous three-dimensional networks. They typically very fragile and brittle due to the inter-particle connections in pearl-necklace-like fractal network. This behavior prevents their wider utility. The present study aims reinforce silica-based gel improve poor mechanical strength through crosslinking silica particles with polyimide incorporating Lucentite STN clay into skeletal silica–polyimide 3-Aminopropyltriethoxysilane (APTES) end-capped polyamic...

Thermoresponsive shape-memory polymer aerogels have been produced from thiol–ene networks of 1,6-hexanedithiol, pentaerythritol tetrakis(3-mercaptopropionate), and triallyl-1,3,5-triazine-2,4,6-trione. The form organogels with either acetonitrile or acetone as the solvent, which can be subsequently removed using supercritical CO2 extraction. resulting nearly quantitative shape fixing recovery a glass transition temperature ranging 42 to 64 °C, serves thermal trigger for effect. porosity 72%...

A series of low density, porous structures were prepared using bis[3-(triethoxysilyl)propyl]disulfide (BTSPD), tetramethylorthosilicate (TMOS) and vinyltrimethoxysilane (VTMS) as precursors via a two-step (acid–base) sol-gel process followed by supercritical CO2 extraction. Using statistical experimental design methodology empirical modelling, the concentrations BTSPD, TMOS VTMS varied in production monoliths found to have significant effect on their bulk porosity, BET surface areas,...

Flexible, conformal polyimide (PI) aerogels with low density, good mechanical properties, and high surface areas have attracted much attention for many potential applications such as lightweight antenna substrates, insulating materials launch vehicles, inflatable structures, aircraft, or space suits. Development improvements to the fabrication of aerogel thin films been reported over last decade meet needs these applications. However, most starting are expensive. In this research, we...

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in 4-chlorophenol (4CP) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable dissolving forming gels both 4CP dichloroacetic acid (DCA) up to a 25 wt %. Highly porous aerogels were prepared through simple solvent exchange followed by one two drying methods removal from wet gel: freeze-drying or supercritical CO2 fluid extraction (SC-drying). field-emission...

Aerogels are promising materials for many aerospace applications, including high-performance antennae and flexible insulation, because of their inherent low density high surface areas. Polymer aerogels, especially polyimide provide excellent mechanical properties beyond traditional silica aerogels while maintaining the required thermal stability. Polyimide aerogel area, porosity, pore volume important properties; however, these measurements traditionally conducted on after removal solvent....

Potential decomposition mechanisms are investigated using density functional theory (DFT) for a set of amide and urea solvents. Reaction energies barriers reported proton hydrogen abstraction, preferred abstraction sites identified. The N–H bond secondary amides the α-hydrogen atoms more susceptible to than other in solvent molecules. Additionally, is favorable at N-alkyl substituents as well that result formation tertiary radicals. All sensitive presence coordinating Li+, but do not depend...

Nonaqueous Li–O2 batteries have the potential to aid in electrification of our society due their relatively high theoretical energy density. Unfortunately, technology suffers from large degrees irreversibility aggressive chemical environment associated with oxidation discharge product lithium peroxide. Herein, we present a study range linear and cyclic amides ureas as aprotic electrolyte solvents for battery, some which show slight increases reversibility relative well-established...

A new series of flexible polyamide (PA) aerogels was synthesized using terephthaloyl chloride (TPC), 2,2'-dimethylbenzidine (DMBZ) and cross-linked with an inexpensive, commercially available tri-isocyanate (Desmodur N3300A) at polymer concentrations 6-8 wt.% total solids repeating units,

The goal of this work was to develop and characterize high-temperature, thermally conductive electrical insulation improve thermal management in high power density electric motors. Polyphenylsulfone (PPSU) films were extruded with up approximately 24 wt% either micro-sized hexagonal boron nitride (hBN) or a mixture micro-and nano-sized hBN particles. effect concentration filler type on the dielectric breakdown voltage, frequency-and temperature-dependent properties, conductivity, aging...

Improving matrix-filler interactions is critical for optimizing dielectric performance in composite insulation; however, the technique used to introduce inorganic fillers into an organic matrix varies its ability satisfactorily reduce size of cavities and interfaces. This study reports effects from changing filler incorporation strategy on rheology, thermal conductivity extruded polyphenylsulfone (PPSU) – hexagonal boron nitride (hBN) insulation. Depending BN host matrix, viscosity, torque,...

Sodium fluoride (NaF) has been found to be an activation agent in exfoliating a hexagonal boron nitride (hBN) platelet, using solvent free method. The procedure was carried out by enhancing the intercalation of ferric chloride (FeCl