We discuss the use of rheological tools to study the phase behavior of aqueous suspension of charged
discotic clay particles of LAPONITE®, a highly contested
system in the literature. While scattering studies suggest a transition from attractive gel (<2
wt%) to repulsive
Wigner glass (>2 wt%), our time-resolved rheometry over 1–4 wt% reveals
linear viscoelastic signatures of a sol-gel
transition typical of crosslinking polymers, indicating a critical gel state with a percolated network, confirmed by cryo-TEM images. This contradicts scattering results and supports an attractive gel across the studied range.
We also discuss
rheological distinctions between
gels and glasses and the source of discrepancy with scattering.
In the second part, we show how Laponite
obeys scaling and hyperscaling laws near the critical gel state, marked by power-law
divergence of zero-shear viscosity, low-frequency modulus, and longest relaxation time, reinforcing its gel-like
microstructure.