title: Unraveling the Mechanism of Nanoscale Mechanical Reinforcement in Glassy Polymer Nanocomposites.
abstract: The mechanical reinforcement of polymer nanocomposites (PNCs) above the glass transition temperature, Tg, has been extensively studied. However, not much is known about the origin of this effect below Tg. In this Letter, we unravel the mechanism of PNC reinforcement within the glassy state by directly probing nanoscale mechanical properties with atomic force microscopy and macroscopic properties with Brillouin light scattering. Our results unambiguously show that the "glassy" Young's modulus in the interfacial polymer layer of PNCs is two-times higher than in the bulk polymer, which results in significant reinforcement below Tg. We ascribe this phenomenon to a high stretching of the chains within the interfacial layer. Since the interfacial chain packing is essentially temperature independent, these findings provide a new insight into the mechanical reinforcement of PNCs also above Tg.
authors.forename: Shiwang
authors.initials: S
authors.lastname: Cheng
authors.forename: Vera
authors.initials: V
authors.lastname: Bocharova
authors.forename: Alex
authors.initials: A
authors.lastname: Belianinov
authors.affiliation: Department of Mechanical Engineering, University of California Berkeley , Berkeley, California 94720, United States.
authors.forename: Shaomin
authors.initials: S
authors.lastname: Xiong
authors.forename: Alexander
authors.initials: A
authors.lastname: Kisliuk
authors.forename: Suhas
authors.initials: S
authors.lastname: Somnath
authors.forename: Adam P
authors.initials: AP
authors.lastname: Holt
authors.forename: Olga S
authors.initials: OS
authors.lastname: Ovchinnikova
authors.forename: Stephen
authors.initials: S
authors.lastname: Jesse
authors.forename: Halie
authors.initials: H
authors.lastname: Martin
authors.forename: Thusitha
authors.initials: T
authors.lastname: Etampawala
authors.forename: Mark
authors.initials: M
authors.lastname: Dadmun
authors.forename: Alexei P
authors.initials: AP
authors.lastname: Sokolov
keywords: Brillouin light scattering; Polymer nanocomposites; band excited atomic force microscopy; interfacial layer; mechanical reinforcement