Dr. Daniele Cangialosi "Universal features in the vitrification and other non-equilibrium phenomena in polymer glasses"

Vitrification on cooling amorphous polymers entails the transformation from a supercooled melt into a non-equilibrium glass. This phenomenon, generally addressed as “the glass transition”, is intimately related to the polymer molecular mobility. In particular, the connection to the main relaxation, that is, the alpha-process, has been generally established. In the present contribution, the vitrification kinetics of poly-4-tert-butylstyrene (PTBS) confined at the micrometer scale is presented [1]. To do so, we have employed fast scanning calorimetry, allowing covering four orders of magnitude in cooling rate. By changing the confinement length scale, that is, the sample size, and the cooling rate, our results show that vitrification can take place in three different regimes. For large samples and at high cooling rates, it follows the standard alpha-process behavior, with large activation energy. On lowering the sample size and the cooling rate, vitrification kinetics shifts to two different regimes with progressively decreasing activation energies. By comparing vitrification data with those of other non-equilibrium phenomena, such as polymer adsorption and dewetting in thin polymer films, we propose that the latter may be driven by the same molecular mechanisms as those relevant for vitrification. Within this framework, all non-equilibrium phenomena in amorphous polymers, depending on the experimental conditions, would be driven by one of the three different regimes relevant for vitrification.

[1] X. Monnier and D. Cangialosi, Phys. Rev. Lett. 121, 137801 (2018)

invited by Dr. Sivasurender Chandran