The influence of water vapor on silica membrane with pore size of ,-4A has been investigated in terms of adsorption properties and percolation effect at 50 and 90 ℃. Two methods are employed： spectroscopic ellipsome...The influence of water vapor on silica membrane with pore size of ,-4A has been investigated in terms of adsorption properties and percolation effect at 50 and 90 ℃. Two methods are employed： spectroscopic ellipsometry for water vapor adsorption and gas permeation of binary mixture of helium and H2O The adsorption behaviors on the silica membrane comply with the first-order Langmuir isotherm. The investigation demonstrates that helium flux through the silica membrane decreases dramatically in presence of H20 molecules. The transport of gas molecules through such small pores is believed not to be continuous any more, whereas it is reasonably assumed that the gas molecules hop from one occupied site to another unoccupied one under the potential gradient. When the coverage of H20 molecules on the silica surface increases, the dramatic decrease of helium flux could be related to percolation effect, where the adsorbed H20 molecules on the silica surface block the hopping of helium molecules.展开更多
The electrical and optical properties of the indium tin oxide （ITO）/epoxy composite exhibit dramatic variations as functions of the ITO composition and ITO particle size. Sharp increases in the conductivity in the v...The electrical and optical properties of the indium tin oxide （ITO）/epoxy composite exhibit dramatic variations as functions of the ITO composition and ITO particle size. Sharp increases in the conductivity in the vicinity of a critical volume fraction have been found within the framework of percolation theory. A conductive and insulating transition model is extracted by the ITO particle network in the SEM image, and verified by the resistivity dependence on the temperature. The dependence of the optical transmittance on the particle size was studied. Further decreasing the ITO particle size could further improve the percolation threshold and light transparency of the composite film.展开更多
Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells （SOFC） and lithium-ion batteries （LIB）. For this, the porous electrode structures of both SOFC and LIB a...Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells （SOFC） and lithium-ion batteries （LIB）. For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB： the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete el- ement approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the con- nectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, es- pecially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of cal- endering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.展开更多
Poly(methyl methacrylate)(PMMA)/polystyrene(PS)/carbon black(CB)and poly(ethyl methacrylate)(PEMA)/PS/CB ternary composite films were obtained using solution casting technique to investigate double percolation effect....Poly(methyl methacrylate)(PMMA)/polystyrene(PS)/carbon black(CB)and poly(ethyl methacrylate)(PEMA)/PS/CB ternary composite films were obtained using solution casting technique to investigate double percolation effect.In both PMMA/PS/CB and PEMA/PS/CB ternary composite films,the CB particles prefer to locate into PS phase based on the results of calculating wetting coefficient,which is also confirmed by SEM images.The conductivity of the films was investigated,and the percolation threshold(￠c)of both ternary composite films with different polymer blend ratios was determined by fitting the McLachlan GEM equation.Conductivity of PMMA/PS/CB ternary composite films showed a typical double percolation effect.However,due to the double emulsion structure of PEMA/PS polymer blends,the PEMA/PS/CB ternary composite films(PEMA/PS=50/50)showed a higher￠c,even CB only located in PS phase,which conflicts with the double percolation effect.A schematic diagram combined with SEM images was proposed to explain this phenomenon.展开更多
基金This work was supported by the Fhndamental Research Funds for the Central Universities （No.XDJK2015C002） and the National Natural Science Foundation of China （No.51402243）. Special thanks are given to Prof. H. J. M Bouwmeester and Dr. N.E. Benes from University of Twente for fruitful discussion.
文摘The influence of water vapor on silica membrane with pore size of ,-4A has been investigated in terms of adsorption properties and percolation effect at 50 and 90 ℃. Two methods are employed： spectroscopic ellipsometry for water vapor adsorption and gas permeation of binary mixture of helium and H2O The adsorption behaviors on the silica membrane comply with the first-order Langmuir isotherm. The investigation demonstrates that helium flux through the silica membrane decreases dramatically in presence of H20 molecules. The transport of gas molecules through such small pores is believed not to be continuous any more, whereas it is reasonably assumed that the gas molecules hop from one occupied site to another unoccupied one under the potential gradient. When the coverage of H20 molecules on the silica surface increases, the dramatic decrease of helium flux could be related to percolation effect, where the adsorbed H20 molecules on the silica surface block the hopping of helium molecules.
基金supported by the National Natural Science Foundation of China(Grant Nos.61222501 and 61335004)
文摘The electrical and optical properties of the indium tin oxide （ITO）/epoxy composite exhibit dramatic variations as functions of the ITO composition and ITO particle size. Sharp increases in the conductivity in the vicinity of a critical volume fraction have been found within the framework of percolation theory. A conductive and insulating transition model is extracted by the ITO particle network in the SEM image, and verified by the resistivity dependence on the temperature. The dependence of the optical transmittance on the particle size was studied. Further decreasing the ITO particle size could further improve the percolation threshold and light transparency of the composite film.
基金supported by the Helmholtz Portfolio "elektrochemische Speicher",particularly the work related to lithium-ion batteriespartially supported as part of the HeteroFoam Center,an Energy Frontier Research Center funded by the U.S.Department of Energy,Office of Science, Basic Energy Sciences(DE-SC0001061)+1 种基金support from the Center for Scientific Computing at the CNSI and MRL:an NSF MRSEC(DMR-1121053) and NSF (CNS-0960316)Australian Research Council Grant DE130101639
文摘Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells （SOFC） and lithium-ion batteries （LIB）. For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB： the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete el- ement approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the con- nectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, es- pecially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of cal- endering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.
基金the China Scholarship Council for funding a scholarship
文摘Poly(methyl methacrylate)(PMMA)/polystyrene(PS)/carbon black(CB)and poly(ethyl methacrylate)(PEMA)/PS/CB ternary composite films were obtained using solution casting technique to investigate double percolation effect.In both PMMA/PS/CB and PEMA/PS/CB ternary composite films,the CB particles prefer to locate into PS phase based on the results of calculating wetting coefficient,which is also confirmed by SEM images.The conductivity of the films was investigated,and the percolation threshold(￠c)of both ternary composite films with different polymer blend ratios was determined by fitting the McLachlan GEM equation.Conductivity of PMMA/PS/CB ternary composite films showed a typical double percolation effect.However,due to the double emulsion structure of PEMA/PS polymer blends,the PEMA/PS/CB ternary composite films(PEMA/PS=50/50)showed a higher￠c,even CB only located in PS phase,which conflicts with the double percolation effect.A schematic diagram combined with SEM images was proposed to explain this phenomenon.
