Entropic Effects on the Mechanical Behavior of Dry Polymer Brushes During Nanoindentation by Atomic Force Microscopy

Abstract

We report on the dependence of the mechanical properties of confined polymers on the film architecture. Compared to spin-coated films, grafted polymer brushes showed higher elastic moduli, which is attributed to entropy effects, and required higher loads to achieve the same residual indentation depth when compared to spin-coated samples. The contribution of entropy changes to the mechanical response of brushes was evaluated. Although qualitative, this study tries for the first time to evaluate this entropic contribution. Therefore, the role of morphology and architecture of the polymer films during mechanical deformation is highlighted, showing that the change of surface thermodynamic properties (entropy in particular) changes accordingly the nanometer scale mechanical properties.