A direct static scattering evidence on the dynamic nature of glass formation process in polystyrene*

The combination of neutron total scattering, high concentration labelling and molecular dynamics (MD) simulation enable us to visualize the temperature dependence most-probable all-atom positions in atactic polystyrene (PS), and find out the dynamic nature of its glass forming. The scattering profiles from MD simulation are in agreement with all of the neutron scattering curves, as well as the X-ray scattering data in literatures at different temperatures. Two main scattering peaks at ~0.6 Å^-1 and 1.4 Å^-1 can thus be allocated. The peak at ~0.6 Å^-1 is from the segment-segment interaction, which is a combination of backbone-backbone and backbone-phenyl interactions. And the peak at 1.4 Å^-1 is mainly from phenyl-phenyl interaction. Below glass formation temperature, both peaks keep almost constant. Their heights jump during glass formation, revealing the melting of the configuration variation and development of dynamic heterogeneity.