Polymer dynamics under 2D nanometer confinement

The effect of confinement on polymer dynamics and the associated liquid-to-glass temperature, T_g, has been an issue of great interest in polymer physics. In this study, we investigate the effect of nanometer confinement on the dynamics of several polymers including cis-1,4-polyisoprene with molecular weights both below and above the entanglement limit. As confining medium we employ self-ordered nanoporous alumina (AAO) with diameters, d, ranging from 400 nm to 25 nm resulting in a broad 2R_g/d range. We employ Broadband Dielectric Spectroscopy (BDS) and Temperature-Modulated Differential Scanning Calorimetry (TMDSC). BDS revealed consistently faster segmental dynamics under confinement with respect to the bulk, leading to a decrease in T_g with increasing degree of confinement (2R_g/d). This is discussed in terms of the role of interfacial energy. In addition, we provide evidence for an intermediate process with an Arrhenius temperature dependence whose dielectric strength increases with increasing degree of confinement. These results are discussed in view of recent theoretical and experimental progress in understanding polymer imbibition in nanopores.