Rheology of Nanosilica-Compatibilized Immiscible Polymer Blends: Formation of a "Heterogeneous Network" Facilitated by Interfacially Anchored Hybrid Nanosilica

Exclusive localization of nanofillers at the interface of immiscible polymer blend has been confirmed to be effective in improving compatibility and facilitating the formation of nanofiller-network with very low percolation threshold, while the rheology of such nanofiller compatibilized blends has seldom been investigated. Herein, we present a systematic rheological study on nanosilica-compatibilized PVDF/PLLA (poly(vinylidene fluoride)/poly(L-lactide)) blends. The linear viscoelastic properties of the systems are evaluated using small amplitude oscillatory shear (SAOS). It is found that the interfacial jammed Janus grafted silica (JGS) located at the interface increases dynamic moduli at low frequency even with very low filler loadings. The nonterminal effects become more pronounced with increasing JGS loadings. Weighted relaxation spectra inferred from SAOS reveals that the shape relaxation of PVDF-droplets is strongly influenced by addition of JGS. The solid-like behavior of JGS-filled blends has been attributed to both the orderly arrangement of JGS at PVDF-PLLA interface and the molecular entanglement between the grafted long tails of JGS with the molecular chains of the component polymers. In other words, JGS at the interface not only promotes strong interfacial interactions between phases, but also stimulates the formation of unique nanoparticle-polymer hybrid network, termed as "heterogeneous network" with the silica as the junctions.