Segmental Equilibration Governs the Adsorption of Confined Polymers

Abstract

Equilibration of the segmental dynamics following a thermal perturbation in the vicinity of T_g and chain adsorption under confinement are closely linked. Here we show that segmental equilibration acts as a kinetic precursor to adsorption. The segmental equilibration time, τ^segm_eq, involves dipole–dipole interactions of polymer segments near the pore walls establishing orientational order. In situ nanodielectric spectroscopy is employed in linear, star-shaped, and bottlebrush polyisoprenes confined in self-ordered nanoporous alumina to determine the second characteristic time, τ_ads. In this mechanism, incoming chains replace the already adsorbed chains by overcoming a low potential barrier U*. Both times exhibit an Arrhenius temperature dependence with identical activation energies and share the same molar mass dependence being independent of the polymer architecture. A relation, τ_ads = exp[E_act/U*]τ^segm_eq, provides the link between adsorption and equilibration and can be used to predict the slower time scale (adsorption) at lower temperatures, where the latter is practically inaccessible.