Counterion distribution of a polyelectrolyte under oscillatory shear

The distribution of counterions of a model polyelectrolyte, sodium polystyrene sulfonate (NaPSS), under oscillatory shear in its aqueous solution is investigated by single molecule fluorescence spectroscopy. By monitoring the local hydronium concentration at the vicinity of PSS main chain using a pH-sensitive fluorescence probe with the application of shear, it is discovered that the local counterion concentration decreases with shear strain and shear rate. Systematic investigations into the dependence on molecular weight and salt concentration as well as polymer concentration are conducted and the results demonstrate a correlation between the saturation shear frequency and the shear strain, showing that the application of the shear alters the structure of the solution against the randomization process caused by diffusion. The results provide helpful experimental evidence to the understanding of rheological properties of polyelectrolyte solutions.