A method for fabricating microvascular networks in fiber‐reinforced composites is presented. The method relies on sacrificial fibers woven into fiber preforms that, when removed by depolymerization ...and volatilization, create 3D microvascular networks inside the composite material. By circulation of functional liquids in the resulting channels, a diverse set of new functionality is demonstrated. Simplicity, robustness, scalability, and reliance on readily available components make this method compatible with composite manufacturing methods.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We examine the transfer of graphene grown by chemical vapor deposition (CVD) with polymer scaffolds of poly(methyl methacrylate) (PMMA), poly(lactic acid) (PLA), poly(phthalaldehyde) (PPA), and ...poly(bisphenol A carbonate) (PC). We find that optimally reactive PC scaffolds provide the cleanest graphene transfers without any annealing, after extensive comparison with optical microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Comparatively, films transferred with PLA, PPA, PMMA PC, and PMMA have a two-fold higher roughness and a five-fold higher chemical doping. Using PC scaffolds, we demonstrate the clean transfer of CVD multilayer graphene, fluorinated graphene, and hexagonal boron nitride. Our annealing free, PC transfers enable the use of atomically-clean nanomaterials in biomolecule encapsulation and flexible electronic applications.
When heated, poly(lactic acid) (PLA) fibers depolymerize in a controlled manner, making them potentially useful as sacrificial fibers for microchannel fabrication. Catalysts that increase PLA ...depolymerization rates are explored and methods to incorporate them into commercially available PLA fibers by a solvent mixture impregnating technique are tested. In the present study, the most active catalysts are identified that are capable of lowering the depolymerization temperature of modified PLA fibers by ca. 100 °C as compared to unmodified ones. Lower depolymerization temperatures allow PLA fibers to be removed from a fully cured epoxy thermoset resin without causing significant thermal damage to the epoxy. For 500 μm diameter PLA fibers, the optimized treatment involves soaking the fibers for 24 h in a solvent mixture containing 60% trifluoroethanol (TFE) and 40% H2O dispersed with 10 wt % tin(II) oxalate and subsequent air-drying of the fibers. PLA fibers treated with this procedure are completely removed when heated to 180 °C in vacuo for 20 h. The time evolution of catalytic depolymerization of PLA fiber is investigated by gel permeation chromatography (GPC). Channels fabricated by vaporization of sacrificial components (VaSC) are subsequently characterized by scanning electron microscopy (SEM) and X-ray microtomography (Micro CT) to show the presence of residual catalysts.
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IJS, KILJ, NUK, PNG, UL, UM
Detonation in suspended aluminum dust is numerically simulated with two-phase flow model. The development and propagation process of detonation in suspended aluminum dust are obtained by numerical ...simulation with distribution of pressure, density, velocity, temperature in the flow field behind shock waves. Parameters of detonation of aluminum dust with different concentrations are calculated. Lower limit of detonation of aluminum dust is also obtained by calculation. At the same concentration, the nano aluminum dust detonation has higher pressure and faster detonation velocity compared with micro aluminum dust. Detonation of suspended aluminum dust in enclosed channel is numerically simulated. The result of numerical simulation shows distinctly that the shock front caused by initiation, and the combustion front of the aluminum particles caused by the high temperature behind the shock front, and the shock front pursued by burning front in aluminum dust and the formation of the detonation. Then the detonation wave is reflected in the wall, and the pressure and temperature increase greatly near the wall.
To study the deflagration to detonation transition process in granular explosive under thermal ignition condition, the conductive burning is introduced into the classical model. The novel space–time ...conservation element and solution element method is applied to solve the mathematical governing equations. The transition process in granular HMX bed which is packed to 85 % of theoretical maximum density is simulated. The development of conductive burning, convective burning and detonation is analyzed. In the early stage, the combustion propagates slowly. It moves no more than 0.2 mm within 8.16 ms. After onset of convective burning, it takes only 20 μs to form a steady detonation with the velocity of 8165 m s
−1
. The time to detonation increases with the decrease in particle diameter.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The reaction model of aluminum particles is the key to successfully simulate the two-phase detonation of aluminum suspensions. In this study, by considering the decomposition of the aluminum oxide ...(Al
2
O
3
) product at high temperature, the reaction model for aluminum particles is improved and is incorporated into the numerical code. Then numerical simulations for two-phase detonations of Al/air mixtures and Al/O
2
mixtures are performed, respectively, the simulated results for the peak pressure and the speed of the two-phase detonation wave are in agreement with the experimental results, which demonstrate the validity of the improved aluminum reaction model. Moreover, the detonation parameters and the distributions of the physical quantities around the detonation wave are analyzed.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We present a numerical study of the mechanisms of the deflagration to detonation transition (DDT) process of explosives to assess its thermal stability. We treated the modeling system as a mixture of ...solid explosives and gaseous reaction products. We utilized a one-dimensional two-phase flow modeling approach with a space-time conservation element and solution element (CE/SE) method. Simulation results show that in the chemical reaction process a plug area of high density with relatively slow chemical reactions preceeds the new violent reactions and the consequent detonation. We found that steady detonation occurs at the regions where physical characteristics, such as pressure, density, temperature, and velocity, peak simultaneously. These simulation results agree well with high-temperature DDT tube experiments.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The introduction of microchannels into traditional composites has numerous applications ranging from self-healing to autonomous cooling materials. However, current approaches for microvascularization ...are hindered by scalability and lack of compatibility with the composite manufacturing proceess. Herein, we present the development of a new procedure for incorporating microchannels into composites that overcome these limitations. Namely, the vaporization of sacrificial component (VaSC). The chosen sacrificial material, poly(lactic acid) (PLA), can be easily incorporated into composites and undergoes a solid-to-gas transition at ca. 280 °C, which allows for the extraction of the gaseous product from the composite leaving hollow spaces in the matrix. The fabrication of a microvascular composite by this method necessitated the development of PLA sacrificial fibers, and three distinct production techniques for producing the desired PLA fibers were explored (chemical modification of commercial PLA fibers, homespun PLA fibers, and micro-structuring of a PLA film). The dissertation also discusses the coated sacrificial fibers (CSFs) as a building block for biomimetic vascular structures. In addition, the fabrication of a microporous battery separator via a similar VaSC approach was developed. In order to improve the safety of automobile battery systems, we sought to apply produce a thermally stable battery separator that prevents cell shortage by establishing a high-temperature fabrication route. A solution containing PLA and polyimide (PI) was cast into form a biphasic film; thermal removal of the PLA phase left a microporous PI film. Experimental evidence showed that the microporous PI film that was fabricated using the PLA sacrificial component had superior thermal properties and could potentially replace current commercial separators.
Four undulating microchannels of a 3D microvascular network are integrated into a structural composite, as revealed by microCT imaging. Jeffrey S. Moore, Scott R. White, and co‐workers report that ...fabrication is accomplished by weaving sacrificial polylactide fibers into the preform prior to conventional composite manufacturing. A post‐curing process depolymerizes the polylactide, leaving behind high‐fidelity, inverse replicas of the original sacrificial fiber.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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