Equilibrium Gels

Equilibrium gels provide physically attractive counterparts of nonequilibrium gels, allowing statistical understanding and design of the equilibrium gel structure. In this project, we assemble two-dimensional equilibrium gels from limited-valency “patchy” colloidal particles and follow their evolution at the particle scale to elucidate cluster-size distributions and free energies. By finely adjusting the patch attraction with critical Casimir forces, we let a mixture of 2-valent and pseudo 3-valent patchy particles approach the percolated network state through a set of equilibrium states. The picture above shows a confocal microscope image of the assembled equilibrium gel, in which the bonding particle patches appear bright. Comparing this equilibrium route with a deep quench, we find that both routes approach the percolated state via the same equilibrium states, revealing that the network topology is uniquely set by the particle bond angles, independent of the formation history. The limited-valency system follows percolation theory remarkably well, approaching the percolation point with the expected universal exponents.