Chain flexibility for tuning effective interactions in blends of polymers and polymer-grafted nanoparticles.

Abstract

We present molecular dynamics simulations of polymer-grafted nanoparticles in a homopolymer matrix to demonstrate the effect of chain flexibility on the potential of mean force (PMF) between various species in the nanocomposite. For a relatively high grafting density of Σg = 0.76 chains/σp(2) (where σp is the polymer monomer diameter), when the brush chain length is significantly smaller than (<∼ 1/4) the matrix chain length, the brushes exhibit autophobic dewetting with matrix polymers resulting in a strong attractive well in the particle-particle PMF. As the chain flexibility is decreased, we observe significant changes in particle-particle and particle-matrix PMFs that are strongly coupled with the length (or molecular weight) of grafted chains. For low molecular weight grafted chains, the change in the well-depth of particle-particle PMFs, with increasing chain stiffness, is non-monotonous, while that for longer grafted chains (still shorter than matrix chains), the attractive well exhibits a monotonous decrease in its depth. The particle-matrix PMF and the matrix penetration depth into the brush layer indicate that wetting of the grafted layer by matrix chains is enhanced with increasing chain stiffness.