Effects on gelation transition by tuning the interaction of solvent-solute molecules in a bridging system

A mixed suspension of large hard spheres and small soft microgels with well-defined bridging interaction is used to construct a new short-range attractive system. Soft poly (N-isopropylacrylamide) microgels ($R_{\mathrm{\thinspace }}=$ 80 nm) are absorbable to the surface of hard polystyrene spheres ($R_{\mathrm{\thinspace }}=$ 960 nm) in aqueous solution. For a constant volume fraction of hard spheres ($\Phi _{\mathrm{MS}})$, gradually increasing amount of microgels ($\Phi _{\mathrm{MG}})$ leads to a liquid-gel-liquid transitions through bridging and steric stabilized mechanisms. Rheological measurements were performed on suspensions with $\Phi_{\mathrm{MS}}$ ranging up to 0.35 to carefully identify the transition boundaries between liquid-like and solid-like behaviors triggered by $\Phi_{\mathrm{MG.\thinspace }}$Meanwhile, neutron scattering technique with Baxter's sticky hard-sphere potential fit was used to investigate the effective interparticle potential at and around the gelation boundaries. By exhibiting a set of experimental results from this explicit model system and comparing with the theoretical data, we try to clarify a debate issue about the relative position of the gel line and the liquid-gas coexistence line in the potential $U -\Phi $ plane.