G. Wall slip during and after shear

During shear

PTV allows us to observe wall slip upon a startup shear. Movie 13 shows no slip at the beginning, sample recoils from the top surface upon slip, undergoes plug-like flow and finally recoil upon shear cessation.

After shear: arrested wall slip

Our PTV observations on step shear described above in D, have provided sufficient insight into a new theoretical picture. Our new theoretical considerations have led us to make powerful predictions of unexpected phenomena. Specifically, we have anticipated occurrence of arrested wall slip: a melt under simple shear would maintain no-slip boundary condition during shear, yet strong slip would occur upon shear cessation. Current theoretical understanding cannot explain this behavior. See Movie 13' for this arrested slip behavior. A paper on it will appear soon in Macromolecules.