Role of Nanoparticle Self-Assembly on Polymer Spherulitic Growth Kinetics

The role of self-assembled nanoparticle (NP) structures on the crystallization kinetics of semicrystalline polymers is systematically investigated. A bimodal brush of polystyrene and poly(methyl methacrylate) is tethered to the surface of silica NPs, which are dispersed into the poly(ethylene oxide) (PEO) matrix. This provides access to a range of self-assembled structures by exploiting the surfactancy of the NPs. While the addition of NPs slows down the spherulite growth rate, it was found that the NP self-assembly does not change the temperature dependence of the spherulite growth rate. Instead, growth rate retardation is mainly attributed to the increase of the PEO melt viscosity and tracks well with the rheologic measurements. Surprisingly, two “universal” trends are observed when measuring the relative spherulite growth reduction as a function of confinement. As long as the self-assembled NP structures are on the nanometer scale, the NPs appear to follow an indistinguishable trend in retarding the spherulitic growth kinetics. However, larger micron-sized aggregates and bare NPs show a weaker effect on the spherulitic growth.