Effect of Star Architecture on the Dynamics of 1,4-cis-Polyisoprene under Nanometer Confinement

Abstract

The dynamics of a series of cis-1,4-polyisoprene stars located inside nanoporous alumina was investigated as a function of functionality, f (2 <= f <= 64), arm molar mass, M (2.6 <= M <= 13.5 kg.mol(-1)), and degree of confinement (0.01 <= 2R(g)/d <= 0.6; where R-g is the radius of gyration and d is the pore diameter) by dielectric spectroscopy. In the bulk, dielectric spectroscopy revealed broadening of the chain modes with the increasing functionality. In addition, a slower dielectric process was found in the vicinity of the soft-colloidal process identified earlier by rheology. The latter associates with the cooperative reorganization of the stars and involves rotational and translational motions. The effect of confinement on the dynamics of stars was stronger than for linear chains. First, the dielectric strength of the normal modes was reduced in the stars and, second, the chain dynamics were slower. The reduced dielectric strength was employed as a measure of the thickness of the interfacial layer. Based on the dielectric strength, we can account for the possible arm star configurations in the vicinity of the pore walls. The slower chain dynamics reflect the increased entanglement density near the pore walls due to extra topological constraints imposed by the adsorbed arms. Functionalization of the pore walls partially restored the dielectric strength of the chain modes. Overall, star-shaped polymers are more prone to adsorption effects when confined in nanopores as compared to linear chains.