Multiscale model for polymer-based nanocomposites considering phase transition behavior

In this study, the particle size effect of polymer-based nanocomposites is estimated quantitatively below and above the glass transition temperature through molecular dynamics (MD) simulations. The thermoelasticity and thermal expansion coefficients (CTE) at each state are calculated for various particle radii under same particle volume fraction in order to characterize the size effect on thermomechanical properties. As a simulation result, the particle size effect is clearly observed in stiffness and CTE both in the glassy and rubbery state of nanocomposites because of the interphase formed by condensed matrix around the embedded particle. In order to develop the sequential bridging model which can explain the particle size effect and thermoelastic behavior in nanocomposites, the MD results are transferred into the multi inclusion micromechanics model which consists of particle, interphase, and matrix. The effective thermal strain is also considered in current micromechanics model to define the thermomechanical properties and the volume fraction of interphase as a function of the embedded particle radius and temperature. It is demonstrated that the current scale bridging model reproduce and predict the thermomechanical properties of the nanocomposites at a wide range of temperatures with reliable accuracy.