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  • 1.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular Dynamics Studies of the Influence of Single Wall Carbon Nanotubes on the Mechanical Properties of Poly(vinylidene fluoride)2013Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 68, s. 73-80Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations and geometry optimizations based on the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field were performed to understand the effect of Single Wall Carbon Nanotubes (SWCNTs) on the mechanical properties of Poly(vinylidene fluoride) (PVDF). In particular, the Young’s modulus, bulk and shear modulus, pullout energy, pullout force, interfacial shear stress and interfacial bonding energy were calculated. The presence of the SWCNTs can increase the Young’s modulus of the systems studied here by 1 GPa in the direction of the SWCNT axis, although this depends on the distance between neighboring SWCNTs. The calculated interfacial shear stress was between 100 and 129 MPa, which is in agreement with results obtained for other SWCNT-polymer systems. The results, and in particular those obtained for the bulk and shear modulus, show that SWCNTs do not have a significant effect on the bulk mechanical properties. Functionalizing the SWCNTs may yield stronger adhesion between the nanotube and the polymer, thereby achieving improved mechanical properties. ⺠Computational studies using molecular dynamics and molecular mechanics. ⺠Effect of single wall carbon nanotubes on the mechanical properties of Poly(vinylidene fluoride). ⺠Alignment of the nanotubes plays a crucial role for the reinforcing effect. ⺠When aligned, an increase in Young’s modulus of approximately 1 GPa could be observed. ⺠The interfacial shear stress was calculated to be in the range of 100–129 MPa.

  • 2.
    Haghighatpanah, Shayesteh
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular-level computational studies of single wall carbon nanotube: polyethylene composites2013Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 69, s. 443-454Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Minimum energy structures of short (3,3) single wall carbon nanotube (SWCNT)–polyethylene (PE) structures, as well as the binding energy between the SWCNT and PE, were obtained from three commonly used molecular mechanics force fields and first principles methods. The molecular force fields were the Dreiding, Universal and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields and the first principles methods included the B3LYP density functional and MP2 post-Hartree Fock methods with, typically, 6-311G, 6-311G(d,p) and 6-311G(2d,2p) basis sets. These calculations show that the results obtained from all force fields are in qualitative agreement with the first principles results, and that PE prefers to be aligned with a non-zero angle along the SWCNT axis, where the angle depends on the force field or first principles method used. This indicates that longer PE chains may wrap around SWCNTs. This was studied using the COMPASS force field with longer (5,5) SWCNTs interacting with a PE chain and, in agreement with the minimum energy calculations, the PE wrapped around the SWCNT thereby increasing the radius of gyration of the PE. This force field was also used to assess the effect of (5,5) SWCNTs on the mechanical properties of PE nanocomposites. The calculated interfacial shear stress and interfacial bonding energy of SWCNT–PE structures was 141.09 MPa and 0.14 N/m. The simulations show that using short SWCNTs as reinforcement does not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWCNTs increased the Young’s modulus in the SWCNT axial direction.

  • 3. Samadikhah, Kaveh
    et al.
    Larsson, Ragnar
    Bazooyar, Faranak
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Continuum-molecular modelling of graphene2012Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 53, nr 1, s. 37-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    membranes using a hierarchical modeling strategy to bridge the scales required to describe and understand the material. Quantum Mechanical (QM) and optimized Molecular Mechanical (MM) models are used to describe details on the nanoscale, while a multiscale continuum mechanical method is used to model the graphene response at the device or micrometer scale. The complete method is obtained on the basis of the Cauchy Born Rule (CBR), where the continuum model is coupled to the atomic field via the CBR and a local discrete fluctuation field. The MM method, often used to model carbon structures, involves the Tersoff--Brenner (TB) potential; however, when applying this potential to graphene with standard parameters one obtains material stress behavior much weaker than experiments. On the other hand, the more fundamental Hartree Fock and Density Functional Theory (DFT) methods are computationally too expensive and very limited in terms of their applicability to model the geometric scale at the device level. In this contribution a simple calibration of some of the TB parameters is proposed in order to reproduce the results obtained from QM calculations. Subsequently, the fine-tuned TB--potential is used for the multiscale modeling of a nano indentation sample, where experimental data are available. Effects of the mechanical response due the calibration are demonstrated.

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