Colloidal gelation induced by ring polymers

The computational results presented here have been achieved using the Vienna Scientific Cluster (VSC).-- QLUSTER Project (Quantum and Classical Ultrasoft Matter), Grant agreement ID: 101072964. Coordinated by CSIC (Centro de Física de Materiales, CFM). Partner/Coordinador principal: Ángel moreno Asegurado. ; We provide unambiguous experimental evidence that ring polymers are stronger depleting agents in colloidal suspensions than their linear counterparts. We use an intermediate volume fraction (ϕc=0.44) colloidal gel based on the classic poly(methyl methacrylate) (PMMA) hard spheres, in which the polystyrene depletant is either linear or ring of the same molar mass or the same size. We systematically increase the depletant concentration from zero (no attraction) to well above the gelation point and find that in the presence of rings, gels are formed at smaller concentrations and possess a larger storage modulus in comparison to those induced by the linear chains. Consequently, the yield stress is enhanced; however, the yield strain (gel deformability) remains concomitantly unaffected. Our experimental findings are in agreement with theoretical calculations based on effective interaction potentials. Hence, polymer architecture is a powerful entropic tool to tailor the strength of colloidal gels. ; S.A.E. acknowledges financial support from the Erwin Schrödinger International Institute for Mathematics and Physics (ESI) as a Senior Research Fellow. We acknowledge support by a FORTH synergy grant (RINGS) and from the European Union (Horizon-MSCA-Doctoral Networks) through the project QLUSTER (HORIZON-MSCA-2021-DN-01-GA101072964). ; Peer reviewed