Playing with Short Range Attractions and Long Range Repulsions Stefano Mossa, Francesco Sciortino, Piero Tartaglia, Emanuela Zaccarelli A new route to the formation of colloidal gels

Motivation: Segre et al PRL 86 (2001)

The quest for the ideal (thermoreversible) gel….model 1) Long Living reversible bonds 2)No Phase Separation 3) No Crystallization Are 1 and 2 mutually exclusive ? The quest Low Temperature Condensation Long Bond Lifetime

Repulsive Glass Attractive Glass Phase Diagram for Square Well (3%) Liquid+Gas Percolation Line Iso- diffusivity lines Spinodal AHS (Miller&Frenkel) A3

How to stay at low T without condensation ? The quest Reasons for condensation (Frank, Hill, Coniglio) Physical Clusters at low T ifthe infinite cluster is the lowest energy state How to make the surface more stable than the bulk ?

Cluster Ground State for the 2n-n potential (Lekkerkerker) The case of an attractive potential

AND POON ADD HERE SOME THING DISNMORE

Groenewold and Kegel Upper Limit Optimal Size How to make negative ?

How do clusters interact ?

Molecular Dynamics Data for Repulsive Yukawa Potential Several number densities n

Are the simulation data providing support for this picture ? The Optimal Size Controls if the system is going to be a cluster phase or an arrested disordered state (Wigner Glass)

The T-dependence of S(q) =0.15

T-dependence of the cluster size distribution

Dynamics... Collective Density autocorrelation function

T=0.15T=0.10

A case in which clustering is.... home made ! Star Polymers high f low f

The disordered arrest problem has been expressed in term of glass transition of cluster Colloidal Gels = Wigner Glasses Cluster Phase stabilized by the competition of Short-Ranged and Repulsive-Long-Ranged interactions