Natural and Mathematical Sciences

Permanent URI for this collectionhttps://hdl.handle.net/10679/313

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Browsing by Institution Author "KAYMAKSÜT, Hande Öztürk"

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    Combining tensile test results with atomistic predictions of elastic modulus of graphene/polyamide-6,6 nanocomposites
    (Elsevier, 2023-06) Batyrov, Merdan; Dericiler, K.; Palabıyık, Büşra Akkoca; Okan, B. S.; Öztürk, Hande; Fındıkçı, İlknur Eruçar; Mechanical Engineering; KAYMAKSÜT, Hande Öztürk; FINDIKÇI, Ilknur Eruçar; Batyrov, Merdan; Palabıyık, Büşra Akkoca
    In this work, we combined tensile test results with atomistic simulations to investigate the effect of filler parameters including distribution, stacking, loading and lateral graphene size on elastic moduli of graphene/PA-6,6 nanocomposites. Stacked and randomly distributed atomistic models were adapted in Molecular Dynamics (MD) simulations to establish the limits of stiffness enhancement in graphene reinforced PA-6,6 nanocomposites with loading ratios changing from 0 to 1 wt%. Experimental results showed that incorporating of 0.3–0.4 wt% graphene loading improved the elastic modulus of the neat polymer by 41.7%−43.5%. While the test sample behaved close to the computational results of the stacked atomistic model at low graphene loadings up to 0.4 wt%, it overshot the predictions of the randomly distributed model at all considered loadings up to 1 wt%. Elastic moduli of graphene-based PA-6,6 nanocomposites increased linearly with graphene loading in the stacked model, however, no such relation was detected in the randomly distributed model. The lower stiffness enhancement provided by the randomly distributed model compared to the stacked model was revealed as the small lateral size of graphene plates in PA-6,6 matrix. As the graphene size increased, the elastic modulus of the graphene dramatically increased, directly improving the elastic modulus of the nanocomposite. The developed computational approach is highly useful to estimate the boundaries of stiffness enhancement provided by graphene dispersions in macroscale nanocomposite samples.
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    Size dependent change of mean square displacement in gold nanocrystals: A molecular dynamics simulation
    (Wiley, 2023-11-01) Batyrow, Merdan; Fındıkçı, İlknur Eruçar; Öztürk, Hande; Mechanical Engineering; FINDIKÇI, Ilknur Eruçar; KAYMAKSÜT, Hande Öztürk; Batyrow, Merdan
    Thermally activated atomic vibrations significantly decrease the x-ray diffraction intensities of nanocrystalline powders. Hence their quantification is critical for accurate structural characterization of small nanocrystals by x-ray diffraction. In this study, atomic vibrations in the form of mean square displacements (MSDs) in 5, 10, 15, 20, and 30 nm diameter spherical gold nanocrystals were computed by molecular dynamics (MD) simulations at room temperature and below. A strong size and temperature dependency of MSD was observed from spherical gold nanocrystals. Moreover, these displacements increased radially from the center of the nanocrystals and reached a maximum at the surface layers due to the presence of undercoordinated surface atoms and their relatively unrestricted motions. High temperature simulations were performed to investigate the evolution of structural stability of nanoparticles with increasing temperature. Surface melting was observed before complete melting of nanocrystals. Results of this work will be useful to understand the effect of nanocrystal size on the amplitude of thermally activated atomic vibrations and their quantification in measured intensities by x-ray diffraction experiments.