Alteration of mechanical properties in polymer films under nanoconfinement

Mastering mechanical properties of nanoconfined polymers is highly demanded yet remains challenging. Pioneering advances have determined Young's modulus (E) of thin polymer films, however, the results showed diverse trends, i.e., E can increase or decrease with reducing film thickness. In this talk, we show that nanoconfinement-induced chain conformations, and entropy-driven (above T_g) or energetic-driven deformations (below T_g) may account for the controversial results. We also show stiffening of PDMS films when lowering film thickness, and alteration of the ratio between elastic and viscous response in ultrathin PDMS films when changing external mechanical loading.