Interfacial entropic interactions tunes fragility and dynamic heterogeneity of confined polymer glasses with embedded nanoparticles.*

The nature of nanoparticle-polymer interfacial layer is known to play a vital role in determining various physical properies of polymer glasses. The influence of interfacial interactions on viscosity, fragility and dynamical heterogeneity of athermal melts are explored in this study¹. Dynamical parameters are studied using X-ray photon correlation spectroscopy and results are corroborated with molecular dynamics simulations. Influence of various microscopic parameters such as interfacial layer diffusivity, matrix chain penetration depth etc on fragility of polymer glasses are demonstrated combining experiment and simulation results. Thin film-substrate interface adsorbed layer effects on dynamical properties of confined glasses are also investigated. Reduction (enhancement) in viscosity is observed for melts with low (high) entropic compatibility parameter, f (molecular weight ratio of graft to matrix chains). Fragility is found to increase with increasing f. Anticorrelation between fragility and dynamical heterogeneity is found in these systems, which are contrary to various earlier studies on glass froming polymers.

1. Begam, Nafisa, et al., Soft Matter, 2018, DOI: 10.1039/C8SM01729H.