(164e) Molecular Dynamics In Amorphous Polymers and Self-Assembling Molecular Glasses

A major challenge in molecular engineering is to understand and control inter- and intra-molecular dynamics. Often, such systems are designed by a trial and error process due to the lack of quantitative information relating to molecular interactions occurring in the desired device configuration (e.g., thin films). Here, we provide a framework to obtain such information based on nanoscale experimental investigations of molecular mobility in two systems of interest: (1) a model polymer system, monodisperse, atactic polystyrene and (2) a series of molecular glasses that form self-assembled ‘physically-linked' polymers by aromatic-pefluorophenyl dispersion interactions.

We show that, for the model system, critical relaxation temperatures and apparent Arrhenius-type activation energies can be deduced via a variety of scanning probe-based techniques including shear modulation force microscopy (SM-FM) and intrinsic friction analysis (IFA). Furthermore, we show that, with regard to IFA data, direct separation of cooperative (entropic) contributions to the apparent Arrhenius activation energy from non-cooperative (enthalpic) contributions is possible by employing a combination of absolute rate theory and the Erying model. As such, the degree of cooperativity for various molecular relaxations in the system is readily apparent.

The second system, a series of three self-assembling molecular glasses with phenyl-perfluorophenyl, naphthyl-perfluorophenyl and anthryl-perfluorophenyl moieties, was also experimentally investigated on the nanoscale using SM-FM and IFA. In these systems, we were able to determine specific temperatures regimes of varying cooperativity. Apparent Arrhenius activation energies and the degree of cooperativity were determined for these regimes, providing fundamental insight into the underlying cooperative molecular relaxation phenomena.