Heterogeneous Glass Transition Behavior of Poly(Ethylene oxide)/Silica Nanocomposites via Atomistic MD Simulations
I. Tanis, Albert J. Power, Antony Chazirakis, Vagelis Harmandaris
Abstract
Adding nanofillers in polymer matrices results in a slowing down of the polymer dynamics for attractive polymer/nanofiller interactions. In this work, we perform atomistic molecular dynamics simulations in poly(ethylene oxide)/silica model nanocomposites to investigate the spatial heterogeneous glass transition behavior of the polymer chains. To address this, we compute both the “thermodynamic” and the “dynamic” glass transition temperature of polymer chains, as a function of the silica loading. The “dynamic” glass transition within specific domains is estimated via a novel method, based on the translational dynamics of the polymer monomers. A clear increase of the glass transition temperature of polymer chains with nanoparticle loading is found. In addition, a spatial gradient in the glass transition behavior is identified, in agreement with experimental studies in polymer nanocomposites with attractive polymer/nanofiller interactions. The local dynamical heterogeneities of polymer chains in the nanocomposites are further examined via a geometric analysis, by probing the evolution of the “slow” polymer regions, as temperature decreases. The “onset” of the glassy state, defined by the percolation of the slow regions, is found in qualitative agreement with the thermodynamic and dynamic approaches.