N. Willenbacher, UNUSUAL THIXOTROPIC PROPERTIES OF AQUEOUS DISPERSIONS OF LAPONITE RD, Journal of colloid and interface science, 182(2), 1996, pp. 501-510
The rheological properties of aqueous dispersions of the synthetic hec
torite clay Laponite RD that form gel-like structures have been invest
igated. Special emphasis has been laid on the phenomenon of thixotropy
. Structural recovery at rest after steady shear is considered a funda
mental thixotropic process and has been characterized by small amplitu
de oscillatory shear measurements. A special sealing technique was use
d to prevent the evaporation of water during these experiments. After
cessation of steady shear \eta\ increases monotonically with time and
even after 16 days no equilibrium viscosity value is reached. A singl
e power law \eta\similar to t(n) holds within the time regime from 10
to 10(6) s. The exponent n=0.13+/-0.02 is independent of clay concent
ration and mechanical pre-treatment of the material. This type of kine
tics has not been reported so far for the thixotropic recovery of any
clay dispersion and it does not fit the common definition of thixotrop
y. The reorganization of the gel structure determining this thixotropi
c phenomenon is interpreted as a cooperative self delaying process sim
ilar to the aging of glassy polymers or precipitation from supersatura
ted solid solutions. (C) 1996 Academic Press, Inc.