Glassy Dynamics of Polymers with Star-Shaped Topologies: Roles of Molecular Functionality, Arm Length, and Film Thickness

作者：Frieberg Bradley R; Glynos Emmanouil; Stathouraki Malvina; Sakellariou Georgios; Green Peter F^*

来源：Macromolecules, 2017, 50(9): 3719-3725.

DOI：10.1021/acs.macromol.7b00091

Structural relaxations of a substance quenched to a temperature T-age below its glass transition temperature T-g enable the structure of the substance to approach equilibrium. This phenomenon, also known as physical aging, has been studied for many decades in bulk linear-chain polymer systems, where the aging rates are generally, to first order, independent of chain length. More recently, the phenomenon has been of keen interest in thin films, where the aging rate is shown to be film thickness H dependent, for films in the thickness range of nanometers to a few hundred nanometers. We show here, based on a study of polystyrene star-shaped polymers of a wide range of functionalities 2 <= f <= 64 and M-arm molecular weights M-arm, that in the limit of sufficiently large values of M-arm. the aging behavior is similar to that of linear chains-independent of M-arm and f. More importantly, in the limit of sufficiently small M-arm and large f, the aging rate is independent of film thickness. Otherwise, the rate is a nonmonotonic function off, for constant M-arm, and H. We present a general physical picture that rationalizes the H, f, and M-arm dependencies of the aging rates of these star-shaped macromolecules-this behavior may be entirely understood in terms of T-age - T-g(x), where T-g(x) is the T-g at distance x from an interface and is a function of H, M-arm, and f.

• 出版日期2017-5-9