Reconciling Computational and Experimental Trends in the Temperature Dependence of Interfacial Mobility in Polymer Films
Jack F. Douglas, Wengang Zhang, Francis W. Starr
Many measurements have indicated that thin polymer ﬁlms in their glass state exhibit an interfacial layer of enhanced mobility that grows in thickness upon heating, as found also in crystalline materials approaching their melting temperature Tm, while simulations and limited measurements of glass-forming liquids at temperature above the glass-transition temperature Tg,c instead exhibit a growing length scale ξ of enhanced mobility upon cooling. To better understand these contradictory trends, we perform molecular dynamics simulations over a temperature regime for which our simulated polymer ﬁlm enters a glassy state, and ﬁnd that the relaxation time within the ﬁlm interior relative to the polymer-air interfacial regime exhibits a maximum near the observed computational glass transition, Tg,c, reconciling previous measurements and simulations of polymer ﬁlms in their glass and liquid states. Correspondingly, we also observe that the interfacial mobility scale exhibits a maximum near Tg,c, but the scale of collective polymer segment exchange motion increases monotonically upon cooling so that the interfacial mobility scale is no longer linked to the scale of collective motion in the glass state.
Journal of Chemical Physics
mobile interfacial layer, amorphous polymer films, crystalline materials, glass transition, density interfacial scale
, Zhang, W.
and Starr, F.
Reconciling Computational and Experimental Trends in the Temperature Dependence of Interfacial Mobility in Polymer Films, Journal of Chemical Physics
(Accessed October 17, 2021)