Direct observation of nanoscale bond-ordering in amorphous polystyrene

Abstract

We used Fluctuation Electron Microscopy (FEM) to measure the correlation length of bond ordering on the nanoscale in atactic polystyrene samples of molecular weight of 350 kg/mol. After annealing, the bond correlations became more pronounced and moved to a shorter length scale of ∼15Å, within the range of agreement with small-angle neutron scattering estimates of persistence length. We also observe on a very local scale (<1 μm) a degree of liquid crystallinity that has not been reported previously in averaged diffraction measurements, most likely because the material is globally, but not locally, isotropic. The method we used, which relies on the sensitivity of FEM to bond–bond correlations, provides a new measure of bond persistence in a polymer, which can be accomplished on nanoscale volumes, particularly important for understanding the structure and properties of nanostructured polymers and polymer thin films and interfaces.