Influence of molecular weight on molecular dynamics and dynamic rheology of polypropylene glycol filled with silica

Abstract

Molecular weight strongly influences the molecular dynamics and rheological responses of nanocomposites, which is far from being well understood. Herein molecular dynamics and rheological behaviors of hydrophilic fumed silica filled unentangled polypropylene glycol (PPG) were investigated as a function of weight averaged molecular weight (M_w) of PPG and volume fraction (∅) of silica. It is shown that M_w does not affect the glassy layers surrounding the nanoparticles and the segmental dynamics of the mobile PPG phase. On the other hand, the mobile PPG phase in the highly filled nanocomposites exhibits an abnormal “more fragile” to “stronger” transition with increasing M_w. The reinforcement and thinning behaviors are stronger in lower-M_w nanocomposites with the “more fragile” mobile PPG phase. The results suggest that reinforcement of nanocomposites affects the dynamic fragility of the mobile phase of the matrix.