Viscoelasticity and Dynamics of Confined Polyelectrolyte/Layered Silicate Nanocomposites: The Influence of Intercalation and Exfoliation

The influence of different confinement regimes on the linear viscoelastic properties of a polyelectrolyte, the protonated poly-[(dimethylamino) ethyl methacrylate] (PDMAEMAH), is investigated. PDMAEMAH is reinforced with the layered silicate montmorillonite (MMT). Neat MMT and MMT treated with sulfobetaine and ammonia-based surfactants (MMT/SB and MMT/NH, respectively) are utilized. Transmission electron microscopy and X-ray scattering show that MMT and MMT/NH produce intercalated morphology, whereas MMT/SB produces an exfoliated morphology. Thus, the polyelectrolyte is under different confinement regimes. The confinement produces the increase of glass transition temperature T-g; however, the increase is larger for the (highly confined) intercalated morphology. Master curves are constructed applying time-temperature superposition. Strikingly, the viscoelastic spectra evidence that the intercalated morphology produces twofold increase of rubber-like modulus, whereas the exfoliated morphology produces over fourfold reduction of rubber-like modulus, both at 3 wt% clay concentration. The reduction of rubber-like modulus suggests that an exfoliated morphology produces disruption of the entanglement density. Analysis in the segmental relaxation regime shows that the intercalated morphology induces longer relaxation times, that is, more dynamics retardation, in correlation with the increase of glass transition temperature. This research paves the road for better understanding of viscoelastic behavior and dynamics of molten polyelectrolytes under confinement.