Shake gels based on Laponite-PEO mixtures: effect of polymer molecular weight

Disc-shaped clay particles (Laponite) with a thickness of 1 nm and a diameter of 25 nm were bridged into a physical gel (shake gel) by poly(ethylene oxide) (PEO) chains under shear. The shake gels formed transformed again into a liquid when the shear stopped. The critical concentrations of Laponite and PEO required for the shake gel formation were determined. The results show that the molecular weight of the polymer chains significantly affects the critical concentrations, as well as the mechanical properties of gels. Shake gels form under certain concentrations of Laponite and PEO, corresponding to a critical surface coverage value (n) over bar (PEO) of the Laponite particles by the polymer chains. The value of (n) over bar (PEO) decreases as the molecular weight of PEO is increased. It was shown that strong gels with a relaxation time longer than 30 min form if the polymer molecular weight is in the range of 2 x 10(5)-3 x 10(5) g/mol.