Temperature dependence of dynamic and mechanical properties in poly (acrylic acid)/graphene oxide nanocomposites
G Kritikos and K Karatasos, MATERIALS TODAY COMMUNICATIONS, 13, 359-366 (2017).
In this work we present a novel methodology with the use of which a new Equation of State (EoS) combined with molecular dynamics (MD) simulations may allow an accurate extrapolation of the dynamic and mechanical properties of polymer nanocomposites in the glassy region. By fitting the temperature dependence of the specific volume to the EoS, the super-Arrhenius increase in the activation energy can be determined. Based on a sigmoidal function of the activation energy, a VFT-like equation is derived which incorporates a new parameter (delta(g)) that determines the extent of the super-Arrhenius region. The new equation identifies two components for the diffusion immediately above and below the glass transition temperature, T-g. Application of the proposed methodology is demonstrated in Poly(acrylic acid) (PAA)/Graphene oxide (GO) nanocomposite systems. A shift of T-g at higher temperatures is predicted due to the addition of GO. Based on the temperature dependence of the viscosity, it is shown that the increase in T-g leads to improved mechanical properties in the composites. In case of an increase in dg at constant T-g, the ratio of the shear modulus of the nanocomposite over the shear modulus of the bulk shows an enhancement consistent with the well-known "Payne effect".
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