Metal powders have long been utilized as the primary fuel component in many conventional pyrolant-based energetic materials. Significant enhancements to their energetic performance are realized with metal powders composed of nanometer-sized particles due largely to the increase in specific surface area (SSA). Reaching the greatest possible weight percent loading of metal nanoparticles requires optimization of the interface between the metal fuel and the polymer matrix. In this work partially fluorinated perfluorocyclobutyl (PFCB) microfibers loaded with nanothermite formulations, composed of aluminum nanoparticles (nAl) coated with different perfluoropolyether (PFPE) oligomers, were successfully fabricated via electrospinning to produce nonwoven mats of energetic thermite microfiber. The resulting energetic textiles were composed of high SSA microfibers with highly uniform fiber diameters at fuel loadings upward of 35 wt % nAl content well dispersed in the fiber matrix. The metalized fibers were found to have smaller and more uniform diameters and possessed nAl loadings an order of magnitude greater than our previously reported polystyrene-based electrospun fiber composites. Furthermore, characterization of fiber morphology, particle dispersion, flame propagation, and the thermal properties of the PFCB/PFPE/nAl based nanothermite textiles are presented in this work to demonstrate a sensitive dependence of many fiber characteristics on the interface between the coated metal particle fuel and the polymer matrix.
Polyvinylidene fluoride (PVDF) presents highly useful piezo and pyro electric properties but they are predicated upon the processing methods and the ensuing volume fraction of the β-phase. Production of PVDF with higher β-phase content for additive manufacturing (AM) is particularly desirable because it can enable the creation of custom parts with enhanced properties. Necessary steps from compounding to the testing of a 3D printed piezo sensitive sensor are presented in this paper. AM process variables and the influence of zinc oxide (ZnO) nanofiller on crystallinity, viscosity, and electromechanical properties of PVDF, have been explored. Fourier-transform infrared spectroscopy (FTIR) measurements confirm that a high cooling rate (HCR) of 30 ∘C·min−1 promotes the conversion of the α-into the β-phase, reaching a maximum of 80% conversion with 7.5–12.5% ZnO content. These processing conditions increase the elastic modulus up to 40%, while maintaining the ultimate strength, ≈46 MPa. Furthermore, HCR 10% ZnO-PVDF produces four times higher volts per Newton when compared to low cooling rate, 5 ∘C·min−1, pristine PVDF. A piezoelectric biomedical sensor application has been presented using HCR and ZnO nanofiller. This technique also reduces the need for post-poling which can reduce manufacturing time and cost.
The title compound was synthesized in near-quantitative yield using nucleophilic aromatic substitution of 4,4′-(hexafluoroisopropylidene)diphenol (BPAF) with perfluoropyridine (PFP). The purity and structure were determined by NMR (1H, 13C, 19F), GC–EIMS, and single-crystal X-ray crystallography.
Improvements to fluoropolymer processing techniques by way of utilizing nanoparticles as drop-in processing aids have pronounced effects on bulk composite properties. In this work, we prepared fluoroalkyl-silanized silica nanoparticles (F-SiNPs, ca. 200 nm) that were solvent-blended with polyvinylenedifluoride (PVDF) in order to prepare composites with varying weight fractions. We demonstrated that the ability to functionalize SiNPs with long fluoroalkylchains that induced co-crystallization with the PVDF matrix, resulting in uniform particle dispersion and improved interlaminate adhesion. This was quantitatively investigated using calorimetry and thermogravimetric analysis, which showed a decrease in the bulk crystallinity of the virgin PVDF from 37% to 10% with minimal 10 wt % F-SiNP loading, rendering a nearly amorphous PVDF. Additional discussions in this work include the effects of various bare and fluoroalkyl-functionalized SiNP loadings on the amorphous and crystalline domains of the PVDF matrix, as well as thermal decomposition.
Improving the performance of composite energetic materials comprised of a solid metal fuel and a source of oxidizer (known as thermites) has long been pursued as thermites for pyrolant flares and rocket propellants. The performance of thermites, involving aluminum as the fuel, can be dramatically improved by utilizing nanometer-sized aluminum particles (nAl) leading to vastly higher reaction velocities, owing to the high surface area of nAl. Despite the benefits of the increased surface area, there are still several problems inherent to nanoscale reactants including particle aggregation, and higher viscosity composited materials. The higher viscosity of nAl composites is cumbersome for processing with inert polymer binder formulations, especially at the high mass loadings of metal fuel necessary for industry standards. In order to improve the viscosity of high mass loaded nAl energetics, the surface of the nAl was passivated with covalently bound monolayers of perfluorinated carboxylic acids (PFCAs) utilizing a novel fluorinated solvent washing technique. This work also details the quantitative binding of these monolayers using infrared spectroscopy, in addition to the energetic output from calorimetric and thermogravimetric analysis.
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