Gelation in dilute aqueous L-cysteine-AgNO₃ solutions

Abstract

Gelation in dilute aqueous L-cysteine solutions containing various electrolytes is studied by rotational viscometry in different dynamic regimes. It is revealed that gels are formed at rather low concentrations of cysteine of no higher than 0.1 vol %. In the linear range of mechanical actions, gels of all examined compositions behave as elastic solid-like media; their elastic moduli, which lie in a range of 10–100 Pa, are independent of frequency and their mechanical losses are low. However, these gels exhibit dualistic properties and can flow at low shear stresses with a Newtonian viscosity on the order of 10³–10⁵ Pa s. On reaching a critical stress (yield point), gels are destroyed, their viscosity decreases by six to seven decimal orders of magnitude, and they are transformed into low-viscosity liquids. At rest, the initial structure and properties are recovered. Mechanisms of percolation network formation are proposed.