A simulation study on the effect of polymer-NP interaction strength on the glass transition temperature and phase separation in polymer nanocomposites

The impact of the interaction strength between polymer and nanoparticles (NPs), epsilon(NP), on the glass transition temperature, T-g, and the phase separation in polymer nanocomposites (PNCs) is explored by employing molecular dynamics simulations. The variation of the T-g with respect to epsilon(NP) shows interesting behaviors at low and high-volume fractions of nanoparticles (f(NP)). For epsilon(NP) < 2, the T-g curves seem to diverge, whereas for epsilon(NP) > 2, they almost coincide. Interestingly, no sign of any phase separation is witnessed in the investigated PNCs at low f(NP). However, at high f(NP), obvious phase separation is noticed for low epsilon(NP). For both cases, there is no phase separation for epsilon(NP) > 2. The measurement of the diffusion constants also reveals that the polymer dynamics become independent of the volume fraction of NPs for epsilon(NP) > 2. We strongly recommend considering this critical value of epsilon(NP) to avoid phase separation and T-g instability in the case of a high-volume fraction of NPs incorporated into PNCs. Briefly, different behaviors of Tg as the interaction strength between nanoparticles and polymer is increased in relevance to different inserted volume fractions of NPs are observed. Thus, the findings of this work could yield a high impact on the experimental techniques implemented in the fabrication and characterization of NPs-Polymers nanocomposites.