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Joonmyung Choi - One of the best experts on this subject based on the ideXlab platform.

  • Elastic Stiffness and filler size effect of covalently grafted nanosilica polyimide composites molecular dynamics study
    ACS Applied Materials & Interfaces, 2012
    Co-Authors: Seunghwa Yang, Joonmyung Choi
    Abstract:

    The filler size-dependent Elastic Stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young’s and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in Elastic Stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization ...

  • Elastic Stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.
    ACS applied materials & interfaces, 2012
    Co-Authors: Seunghwa Yang, Joonmyung Choi, Maenghyo Cho
    Abstract:

    The filler size-dependent Elastic Stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in Elastic Stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface.

Seunghwa Yang - One of the best experts on this subject based on the ideXlab platform.

  • Elastic Stiffness and filler size effect of covalently grafted nanosilica polyimide composites molecular dynamics study
    ACS Applied Materials & Interfaces, 2012
    Co-Authors: Seunghwa Yang, Joonmyung Choi
    Abstract:

    The filler size-dependent Elastic Stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young’s and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in Elastic Stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization ...

  • Elastic Stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.
    ACS applied materials & interfaces, 2012
    Co-Authors: Seunghwa Yang, Joonmyung Choi, Maenghyo Cho
    Abstract:

    The filler size-dependent Elastic Stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in Elastic Stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface.

Maenghyo Cho - One of the best experts on this subject based on the ideXlab platform.

  • Elastic Stiffness and filler size effect of covalently grafted nanosilica polyimide composites: molecular dynamics study.
    ACS applied materials & interfaces, 2012
    Co-Authors: Seunghwa Yang, Joonmyung Choi, Maenghyo Cho
    Abstract:

    The filler size-dependent Elastic Stiffness of nanosilica (α-quartz)-reinforced polyimide(s-BPDA/1,3,4-APB) composites under the same volume fraction and grafting ratio conditions was investigated via molecular dynamics(MD) simulations. To enhance the interfacial load transfer efficiency, we treated the surface oxygen atoms of the silica nanoparticle with additional silicon atoms attached by a propyl group to which the aromatic hydrocarbon in the polyimide is directly grafted. As the radius of the embedded nanoparticle increases, the Young's and shear moduli gradually decrease, showing a prominent filler size effect. At the same time, the moduli of the nanocomposites increase as the grafting ratio increases. The contribution of different nanoparticles to the filler size dependency in Elastic Stiffness of the nanocomposites can be elucidated by comparing the normalized adhesive interaction energy between the particle and matrix which exhibits prominent filler size dependency. Because of the immobilization of the matrix polymer in the vicinity of the nanoparticles, which was confirmed by the self-diffusion coefficient, the highly grafted interface is found to bring about a greater reinforcing effect than the ungrafted interface.

Y C Zhou - One of the best experts on this subject based on the ideXlab platform.

  • ab initio Elastic Stiffness of nano laminate mxm 2 x alc m and m ti v and cr solid solution
    Journal of Physics: Condensed Matter, 2004
    Co-Authors: J Y Wang, Y C Zhou
    Abstract:

    We have investigated the Elastic Stiffness and electronic band structure of nano-laminate solid solutions, where M and and Cr, by means of the ab initio pseudopotential total energy method. The second-order Elastic constants, bulk moduli and anisotropic Young's moduli are computed for the solid solutions, in which x is changed from 0 to 2 in steps of 0.5. The bulk moduli of is found to be approximately the average of the two end M2AlC and phases as the substitution content x, as well as the valence electron concentration (VEC), varies in the compounds. On the other hand, the shear modulus c44, which by itself represents a pure shear shape change and has a direct relationship with hardness, saturates to a maximum as VEC is in the range 8.4?8.6. It implies that solid solution hardening may be operative for alloys having VEC values in this range. Furthermore, trends in the Elastic Stiffness are interpreted in terms of the electronic band structure. We show that monotonically incrementing the bulk moduli is attributed to the occupying states involving transition-metal d?Al p covalent bonding and metal-to-metal dd bonding. The maximum in c44, on the other hand, originates from completely filling the shear resistive transition-metal d?Al p bonding states. Most importantly, we predict a method to optimize the desired Elastic Stiffness by properly tuning the valence electron concentration of ceramics.

  • Ab initio Elastic Stiffness of nano-laminate (MxM '(2-x))AlC (M and M ' = Ti, V and Cr) solid solution
    Journal of Physics: Condensed Matter, 2004
    Co-Authors: J Y Wang, Y C Zhou
    Abstract:

    We have investigated the Elastic Stiffness and electronic band structure of nano-laminate solid solutions, where M and and Cr, by means of the ab initio pseudopotential total energy method. The second-order Elastic constants, bulk moduli and anisotropic Young's moduli are computed for the solid solutions, in which x is changed from 0 to 2 in steps of 0.5. The bulk moduli of is found to be approximately the average of the two end M2AlC and phases as the substitution content x, as well as the valence electron concentration (VEC), varies in the compounds. On the other hand, the shear modulus c44, which by itself represents a pure shear shape change and has a direct relationship with hardness, saturates to a maximum as VEC is in the range 8.4?8.6. It implies that solid solution hardening may be operative for alloys having VEC values in this range. Furthermore, trends in the Elastic Stiffness are interpreted in terms of the electronic band structure. We show that monotonically incrementing the bulk moduli is attributed to the occupying states involving transition-metal d?Al p covalent bonding and metal-to-metal dd bonding. The maximum in c44, on the other hand, originates from completely filling the shear resistive transition-metal d?Al p bonding states. Most importantly, we predict a method to optimize the desired Elastic Stiffness by properly tuning the valence electron concentration of ceramics.

Yanchun Zhou - One of the best experts on this subject based on the ideXlab platform.

  • theoretical Elastic Stiffness structure stability and thermal conductivity of la2zr2o7 pyrochlore
    Acta Materialia, 2007
    Co-Authors: Jingyang Wang, Yanchun Zhou, Ting Liao, Fangxing Li
    Abstract:

    Elastic Stiffness and electronic structure of La2Zr2O7 were calculated by means of the first-principles pseudopotential total energy method. The equation of state (EOS), Elastic parameters (including the full set of second-order Elastic coefficients, bulk modulus and Young's modulus) and Elastic anisotropy were reported. Furthermore, pressure dependence of crystal structure, electronic structure, and bond strengths were investigated. It is found that, although the La2Zr2O7 lattice is stable at high pressures, its electronic structure and atomic bonding are definitely disturbed by the applied pressure. The crystal structure of La2Zr2O7 approaches that of the fluorite-type lattice at high pressures. The strengths of different interatomic bonds in La2Zr2O7 are examined by considering bond-length contractions at various pressures. In addition, the results based on quantum-mechanical-scale calculation clarify the nature of low thermal conductivity of La2Zr2O7 at elevated temperatures. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • theoretical Elastic Stiffness structure stability and thermal conductivity of la2zr2o7 pyrochlore
    Science & Engineering Faculty, 2007
    Co-Authors: Jingyang Wang, Yanchun Zhou, Ting Liao, Fangxing Li
    Abstract:

    Elastic Stiffness and electronic structure of La 2 Zr 2 O 7 were calculated by means of the first-principles pseudopotential total energy method. The equation of state (EOS), Elastic parameters (including the full set of second-order Elastic coefficients, bulk modulus and Young's modulus) and Elastic anisotropy were reported. Furthermore, pressure dependence of crystal structure, electronic structure, and bond strengths were investigated. It is found that, although the La 2 Zr 2 O 7 lattice is stable at high pressures, its electronic structure and atomic bonding are definitely disturbed by the applied pressure. The crystal structure of La 2 Zr 2 O 7 approaches that of the fluorite-type lattice at high pressures. The strengths of different interatomic bonds in La 2 Zr 2 O 7 are examined by considering bond-length contractions at various pressures. In addition, the results based on quantum-mechanical-scale calculation clarify the nature of low thermal conductivity of La 2 Zr 2 O 7 at elevated temperatures.

  • first principles Elastic Stiffness of lapo4 monazite
    Applied Physics Letters, 2005
    Co-Authors: Jingyang Wang, Yanchun Zhou
    Abstract:

    In this letter, the full set of Elastic coefficients of LaPO4 monazite is presented based on the first-principles plane-wave pseudopotential total energy method. Mechanical parameters (bulk modulus, shear modulus, Young's moduli, and Poisson's ratio) are also presented and compared with experimental results for polycrystalline monazite. The responses of electronic structure and chemical bonds to a series of {010} shear strains are examined in order to study the mechanism of low shear strain resistance. The results show that small shear moduli originate from the inhomogeneous strengths of atomic bonds. For example, the weak La-O bonds accommodate the shear strain locally, while the PO4 tetrahedra are almost rigid. The theoretical Elastic Stiffness may be useful to understand the deformation mechanisms of LaPO4 monazite. (c) 2005 American Institute of Physics.

  • dependence of Elastic Stiffness on electronic band structure of nanolaminate m2alc m ti v nb and cr ceramics
    Physical Review B, 2004
    Co-Authors: Jingyang Wang, Yanchun Zhou
    Abstract:

    We investigate the Elastic Stiffness and electronic band structure of nanolaminate M2AlC (M=Ti,V,Nb, and Cr) ceramics by using the ab initio pseudopotential total energy method. The relationship between Elastic Stiffness and valence electron concentration (VEC) is discussed. The results show that the bulk and shear moduli enhance monotonously as VEC increases in M2AlC. The shear modulus c(44), which by itself represents a pure shear shape change and is directly related to hardness, reaches its maximum when the VEC is in the range of 8.4-8.6. This implies that the bulk modulus, shear modulus, and hardness vary in different trends when the VEC changes in M2AlC. Furthermore, trends in the Elastic Stiffness are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level of M2AlC. We show that increments of bulk and shear moduli originate from additional valence electrons filling states involving Md-Alp covalent bonding and metal-to-metal t(2g) and e(g) orbitals. For the case of c(44), strengthening the M-Al pd covalent bonds effectively enhances the shear resistance and excessive occupation of dd orbitals gives rise to a negative contribution. The maximum of c(44) is attributed to the complete filling of the Md-Alp bonding states.