To enhance the nucleation and crystallization properties of polyester (e.g., polyethylene terephthalate, PET), core-shell structured particles are used to improve these properties by controlling the inorganic di...To enhance the nucleation and crystallization properties of polyester (e.g., polyethylene terephthalate, PET), core-shell structured particles are used to improve these properties by controlling the inorganic dispersion properties in the polymers. In the paper, monodisperse particles of silica/polystyrene (PS) are prepared with both dispersion and emulsion polymerization techniques. The monodisperse silicon dioxide particles are first prepared with the seed growth method and modified by the coupling agents. Silica is properly modified with KH-570, and its size deviation is 3.0% or so. The modified silica then reacts with the mixture of ethanol, water medium, and monomer of styrene under dispersion polymerization. Results show that the dispersion polymerization technique is more suitable for monodisperse core-shell SiO2/PS particles than that of the emulsion. The morphology and molecular structure of the core-shell particles are investigated with the transmission electron microscope (TEM), and fourier transform infra-red spectroscopy (FTIR). The results show that the modified silica particles are successfully encapsulated with polystyrene. The average number of silica particles encapsulated into each polystyrene sphere decreases when the size of silica particles increases from 50 nm to 600 nm, and will approach one when the silica is greater than 380nm in size. The mass ratio for silica/PS particles in emulsion polymerization is 4.7/1, lower than that of 6.8/1 for dispersion polymerization, which is the first reported optimized data for preparing the similar monodisperse composite particles. Thus, the PS shell in the former is thinner than that in the latter.展开更多
Natural aluminum particles have the core-shell structure.The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences.The dynamic behavior of the structural...Natural aluminum particles have the core-shell structure.The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences.The dynamic behavior of the structural response of aluminum core-shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications.In this paper,an aluminum particle combustion experiment in a detonation environment is conducted and analyzed;the breakage factors of aluminum particles shell in detonation environment are analyzed.The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster.The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave.The detonation wave impacts the aluminum particles,resulting in shell cracking,and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product,the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.展开更多
Rupturing the alumina shell(shell-breaking)is a prerequisite for releasing energy from aluminum powder.Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina she...Rupturing the alumina shell(shell-breaking)is a prerequisite for releasing energy from aluminum powder.Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina shell.COMSOL Multiphysics was used to simulate and analyze the shell-breaking response of micron-scale aluminum particles with different particle sizes at 650℃in vacuum.The simulation results show that the thermal stability time and shell-breaking response time of 10μm–100μm aluminum particles are 0.15μs–11.44μs and 0.08μs–3.94μs,respectively.They also reveal the direct causes of shell breaking for aluminum particles with different particle sizes.When the particle size is less than 80μm,the shell-breaking response is a direct result of compressive stress overload.When the particle size is between80μm and 100μm,the shell-breaking response is a direct result of tensile stress overload.This article provides useful guidance for research into the energy release of aluminum powder.展开更多
Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine （〈100nm） ammonium sul...Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine （〈100nm） ammonium sulfate particles internally mixed with either succinic acid （slightly soluble） or levoglucosan （soluble） in different mixing structures （core-shell vs. well-mixed} were measured using a hygroscopicity tandem differential mobility analyzer （HTDMA）. During the hydration process （6-92% relative humidity （RH））, the size of core-shell particles （ammonium sulfate and succinic acid） remained unchanged until a slow increase in particle size occurred at 79Y~ RH; however, an abrupt increase in size （i.e., a clear deliquescence） was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles （80：20 by volume）. This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan＇s higher solubility relative to succinic acid. The growth factor （GF） of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.展开更多
Core/shell type acrylic-polyurethane hybrid microemulsions in which polyurethaneas the shell and acrylic polymer as the core were prepared successfully. Different cross-link-ing structures between core and shell can b...Core/shell type acrylic-polyurethane hybrid microemulsions in which polyurethaneas the shell and acrylic polymer as the core were prepared successfully. Different cross-link-ing structures between core and shell can be formed by introducing hydroethyl acrylate andadipoyl dihydrazine at the ends of the polyurethane chains. The photon correlation spec-troscopy studies revealed that the mean particle size of the emulsions were smaller than 200nm. The particle morphology results revealed the core/shell structure of the uncross-linkingtype microemulsions and interpenetrating networks of the cross-linking type microemulsions.展开更多
文摘To enhance the nucleation and crystallization properties of polyester (e.g., polyethylene terephthalate, PET), core-shell structured particles are used to improve these properties by controlling the inorganic dispersion properties in the polymers. In the paper, monodisperse particles of silica/polystyrene (PS) are prepared with both dispersion and emulsion polymerization techniques. The monodisperse silicon dioxide particles are first prepared with the seed growth method and modified by the coupling agents. Silica is properly modified with KH-570, and its size deviation is 3.0% or so. The modified silica then reacts with the mixture of ethanol, water medium, and monomer of styrene under dispersion polymerization. Results show that the dispersion polymerization technique is more suitable for monodisperse core-shell SiO2/PS particles than that of the emulsion. The morphology and molecular structure of the core-shell particles are investigated with the transmission electron microscope (TEM), and fourier transform infra-red spectroscopy (FTIR). The results show that the modified silica particles are successfully encapsulated with polystyrene. The average number of silica particles encapsulated into each polystyrene sphere decreases when the size of silica particles increases from 50 nm to 600 nm, and will approach one when the silica is greater than 380nm in size. The mass ratio for silica/PS particles in emulsion polymerization is 4.7/1, lower than that of 6.8/1 for dispersion polymerization, which is the first reported optimized data for preparing the similar monodisperse composite particles. Thus, the PS shell in the former is thinner than that in the latter.
基金Project supported by the National Natural Science Foundation of China(Grant No.11772058)
文摘Natural aluminum particles have the core-shell structure.The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences.The dynamic behavior of the structural response of aluminum core-shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications.In this paper,an aluminum particle combustion experiment in a detonation environment is conducted and analyzed;the breakage factors of aluminum particles shell in detonation environment are analyzed.The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster.The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave.The detonation wave impacts the aluminum particles,resulting in shell cracking,and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product,the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.
基金the National Natural Science Foundation of China(Grant No.11802160)。
文摘Rupturing the alumina shell(shell-breaking)is a prerequisite for releasing energy from aluminum powder.Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina shell.COMSOL Multiphysics was used to simulate and analyze the shell-breaking response of micron-scale aluminum particles with different particle sizes at 650℃in vacuum.The simulation results show that the thermal stability time and shell-breaking response time of 10μm–100μm aluminum particles are 0.15μs–11.44μs and 0.08μs–3.94μs,respectively.They also reveal the direct causes of shell breaking for aluminum particles with different particle sizes.When the particle size is less than 80μm,the shell-breaking response is a direct result of compressive stress overload.When the particle size is between80μm and 100μm,the shell-breaking response is a direct result of tensile stress overload.This article provides useful guidance for research into the energy release of aluminum powder.
基金supported by the National Leading Research Laboratory Program funded from the National Research Foundation of Korea (NRF) (No. 2011-0015548)an NRF grant (NRF-C1ABA001-2012-0005668)
文摘Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine （〈100nm） ammonium sulfate particles internally mixed with either succinic acid （slightly soluble） or levoglucosan （soluble） in different mixing structures （core-shell vs. well-mixed} were measured using a hygroscopicity tandem differential mobility analyzer （HTDMA）. During the hydration process （6-92% relative humidity （RH））, the size of core-shell particles （ammonium sulfate and succinic acid） remained unchanged until a slow increase in particle size occurred at 79Y~ RH; however, an abrupt increase in size （i.e., a clear deliquescence） was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles （80：20 by volume）. This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan＇s higher solubility relative to succinic acid. The growth factor （GF） of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.
文摘Core/shell type acrylic-polyurethane hybrid microemulsions in which polyurethaneas the shell and acrylic polymer as the core were prepared successfully. Different cross-link-ing structures between core and shell can be formed by introducing hydroethyl acrylate andadipoyl dihydrazine at the ends of the polyurethane chains. The photon correlation spec-troscopy studies revealed that the mean particle size of the emulsions were smaller than 200nm. The particle morphology results revealed the core/shell structure of the uncross-linkingtype microemulsions and interpenetrating networks of the cross-linking type microemulsions.
