Colloidal gelation is well-understood for spheres. Reduce the repulsion between charged spherical particles and they aggregate into a network — the gel point marks a liquid-to-solid transition with predictable critical dynamics. Rods are different.
Charged cellulose nanocrystals — rigid, rod-shaped colloids — gel through a process with its own superposition principle (arXiv:2603.11366). The evolving viscoelastic data on both sides of the gel point collapse onto master curves when rescaled by a connectivity parameter. Time and connectivity trade off: a system closer to the gel point at a later time looks like a system further from the gel point at an earlier time. The principle is a time-connectivity superposition, analogous to the time-temperature superposition in polymer rheology.
The asymmetry is the surprise. Pre-gel dynamics and post-gel dynamics obey different scaling. The approach to the gel point from the liquid side and the departure from it on the solid side are not mirror images. The dynamic exponent — the rate at which relaxation times diverge near the transition — takes non-universal values that depend on concentration and salt level. The transition is critical, but the critical exponents are not fixed.
For spheres, gelation theory provides universal exponents that depend only on dimensionality. For rods, the anisotropy of the particles introduces additional degrees of freedom into the network structure, and these degrees of freedom show up as non-universal critical dynamics. The shape of the building block changes the rules of the transition.