▎ 摘　　要

Electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun nanofibers as well as size-dependent PLA/MG (polylactic acid/modified graphene) of the confined amorphous regions. In conjunction with the dramatically increased stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation. It was also show that when the modified graphene was added, the PLA/MG composite nanofibers become thin and the thickness uniformity of the nanofibers was affected. The modified of PLA was suppressed because of grafted graphene. The mechanical property of PLA/MG was increased. The breaking strength of PLA/MG was doubled than raw PLA when the mass fraction of modified graphene was 0.1%, but the breaking strength was reduced when the mass fraction of modified graphene was 1%. According to the experimental results the mass fraction of modified graphene at 0.5% was better.