Viscoelasticity and Dynamics of Intercalated Polymer/Bentonite Nanocomposites

This research investigates confinement-induced dynamics retardation behavior in intercalated acrylic/clay nanocomposites. Nanostructured waterborne latex contains up to 3 wt% nanoclay, and transmission electron microscopy shows well-dispersed intercalated morphology. Dynamics in the melt is analyzed using the time-temperature superposition principle. Confinement induces dynamics retardation, and the entanglement relaxation time (e) increases over an order of magnitude. The cooperative motion retardation also reduces viscous dissipation, as measured by the damping tan. Moreover, the rubbery modulus increases >10-fold. The increase of rubbery modulus suggests that confinement hinders chain mobility. The system is then naturally segregated, with intercalated chains having slow dynamics. Hence, thermal analysis of freshly cast films shows one broad glass transition with temperature T-g,T-i for all the nanocomposites, and upon annealing the nanocomposites exhibits two T-g's. The T-g,T-high suggests regions of reduced chain mobility (i.e., intercalated chains); the T-g,T-low is associated to the bulk material with regions of higher mobility. The breadth T-g,T-high - T-g,T-low increases with clay content indicating that the regions of fast and slow dynamics become more decoupled as confinement increases.