Characterization of PS and PMMA Chain Mobility Confined in AAO

Understanding and controlling the glass transition temperature (T_g) and dynamics of polymers in confined geometries are of significance in both academia and industry. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) nanofibers confined in AAO templates are investigated. At fast cooling rates, the imparted thermal stress would overcome the yield stress of polymer and peel chains off the pore walls, while at slow cooling rates, chains are kept in contact with the pore walls due to timely dissipation of the produced thermal stress during vitrification. Results of differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) clearly identified two glass transition temperatures during an ultraslow cooling process (0.1K/min) across the T_g. A dramatic change in the glass transition behaviors is detected when the cooling rate is changed from 40 to 0.1 K/min, which reflects the inherent evolution between the shell and the core through a non-equilibrium interlayer. Our findings provide insight into achieving stable glassy polymer structures confined in nanopores by balancing the geometric curvature, interfacial interactions and cooling rate.