Control of Particle Dispersion with Autophobic Dewetting in Polymer Nanocomposites

Abstract

Good particle dispersion in polymer nanocomposites (PNCs) is often hampered by autophobic dewetting where the matrix polymers are expelled from the grafted polymer, generally believed to result in increased particle aggregation and enhanced mechanical properties in dilute particle regime. However, we found that autophobic dewetting with highly extended short-chain polymers improves/disrupts particle dispersity, strongly dependent on particle volume fraction. Under strong autophobic condition given with the highmolecular-weight ratio between the matrix, P, and grafted polymer, N, (P/N >> 1), silica nanoparticles grafted with dopamine-modified poly(ethylene glycol) (DOPA-mPEG) brush polymer are dispersed in the PEG matrix by varying the surface grafting rate. In the dilute particle regime, we found that increasing grafting rate ironically improves particle dispersion and reduces the shear modulus as dewetted polymers cannot bridge the particles. In the concentrated particle regime, on the contrary, particles become more aggregated and the corresponding mechanical strength increases with grafting rate as a denser particle network is formed by depletion attractions. Investigating the microstructures, dynamics, and rheological properties of PNCs with small-angle X-ray scattering, time-domain proton NMR, and oscillatory rheometry experiments, respectively, this study provides additional design guidelines for controlling the detailed structure and properties of PNCs.