Shear induced self-thickening in chitosan-grafted polyacrylamide aqueous solution†
A remarkable shear induced self-thickening of chitosan-graft-polyacrylamide aqueous solution was observed. After the polyelectrolyte solution presenting shear thinning was subjected to a high-rate shear for several minutes, their viscosities recovered and then a much higher zero shear viscosity than the original one appeared. Obviously, the self-thickening differs from conventional shear thickening or viscous recovery, as reported previously. The mechanism of self-thickening was investigated by rheological methods together with TEM, 1H NMR and DLS, etc. It was found that some aggregates exist in original chitosan-graft-polyacrylamide aqueous solution and the scale of such aggregations would become larger within several minutes after a strong shear. The thickening was proven to be the result of an enhanced scale of GPAM aggregation in aqueous solution, and the mechanism of aggregation was proven to be intermolecular hydrogen bonding effects. Besides, the shear-induced self-thickening appears to be facile, maintainable and easily controllable by changing the shear conditions.