Search

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 (ϕ_{c}=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.

The mixture of nanoparticles and polymers can dramatically alter the dynamics of the resulting system, but the detail is still under debate. Here, Baeza et al. show the formation of a percolated network by polymer bridging between adjacent nanoparticles as nanoparticle concentration increases.