Fracture Toughness of Polymer Interfaces Compatibilized with Nanoparticle Brushes

Abstract

Surface-active particles at immiscible polymer/polymer interfaces can provide unparalleled stability against droplet coalescence. However, they often deteriorate the fracture toughness (Gc) of the interface because their rigid cores act as stress concentrators. Here, we draw on the knowledge developed for the interfacial strengthening mechanisms of block and random copolymers to design analogous particle-based systems. We use silica nanoparticles “grafted-from” with poly(styrene-r-methyl methacrylate) (PS-r-PMMA) chains to strengthen PS/PMMA interfaces. In this manner, the silica cores suppress droplet coalescence, while the PS-r-PMMA grafts entangle with the homopolymers and transmit stress across the interface. Interestingly, we show that Gc for the interfaces compatibilized with these particle brushes can exceed that of the interfaces compatibilized with ungrafted copolymer analogues. Rheology experiments attribute this phenomenon to increased connectivity between the entanglement points in these hybrid particle brush systems.