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Gelation of Large Hard Particles with Short-Range Attraction Induced by Bridging of Small Soft Microgels



Junhua Luo, Guangcui Yuan, Chuanzhuang Zhao, Charles C. Han, Jie Chen, Yun Liu


In this study, mixed suspensions of large hard polystyrene microsphere and small poly(N-isopropylacrylamide) microgel is used as model systems to investigate the static and viscoelastic properties of suspensions which go through liquid to gel transitions. The microgels cause short-range attraction between microspheres through bridging and depletion mechanism whose strength can be tuned by the microgel concentration. Rheological measurements are performed on suspensions with the volume fraction (φ)of microsphere ranging from 0.02 to 0.15, and the transitions from liquid-like to solid-like behaviors triggered by the concentration of microgels are carefully identified. Three gel lines, two due to bridging attraction under unsaturated conditions and one due to depletion attraction under over saturated situation, are obtained. Ultra-small angle neutron scattering is used to probe the thermodynamic properties of suspensions approaching to the liquid-solid transitions. Baxter¿s sticky hard-sphere model is used to extract the effective inter-microsphere interaction introduced by bridging or depletion of microgels despite the fact that the physical mechanisms of bridging attraction and depletion attraction are different at a molecular level. It is found that the strength of attraction (characterized by a single stickiness parameter τ ) on the gel lines formed either by bridging or by depletion mechanism are similar. Moreover, the τ values for the gel lines are very close to the theoretical value for spinodal line in the τ - φ phase diagram predicted by Baxter¿s model. This indicates that the nature of gel state may have the same thermodynamic origins, independent of the detailed mechanism of the short-range attraction (bridging or depletion).
Soft Matter


USANS, Neutron Scattering, Gelation, Colloidal Interaction


Luo, J. , Yuan, G. , Zhao, C. , Han, C. , Chen, J. and Liu, Y. (2015), Gelation of Large Hard Particles with Short-Range Attraction Induced by Bridging of Small Soft Microgels, Soft Matter, [online], (Accessed April 14, 2024)
Created March 17, 2015, Updated October 12, 2021