Importance of Sub-Nanosecond Fluctuations on the Toughness of Polycarbonate Glasses
Christopher L. Soles, Kanae N. Ito, Adam B. Burns, Edwin P. Chan, Robert M. Dimeo, Madhu Sudan Tyagi, Albert F. Yee, Jianwei Liu
This article explores the relationship between the nano- to picosecond dynamics, as quantified by elastic incoherent neutron scattering, in polycarbonate (PC) glasses with their mechanical toughness. We establish a robust correlation between mechanical toughness and these fast relaxations, suggesting that they are a critical pathway for dissipating energy under impact conditions. This understanding is developed across a series of PCs, where the impact strength is either systematically increased through the incorporation of 1,4-cyclohexyl linkages into the PC backbone or diminished through the addition of antiplasticizer molecules that embrittle the glass. Across this homologous series, a connection emerges between the level of anharmonicity in mean square-atomic displacements of different PCs and their impact strength. We interpret the level anharmonicity in these fast dynamics as a metric of the collective, many-atom relaxations, suggesting that collective relaxation processes on the timescale of nano- to picosecond are critical for toughness in polymer glasses.