Influence of surfactants on shear-thickening behavior in concentrated polymer dispersions

Concentrated dispersions consisting of 310 nm poly(styrene-ethylacrylate) nanospheres and ethylene glycol, which exhibited pronounced shear-thickening behavior, were prepared in this work. The influence of surfactants on their shear-thickening behavior was investigated, which indicated that the surfactants affected the shear-thickening behavior by changing the surface force and interparticle force. Various surfactants, such as cationic, anionic, nonionic, and zwitterionic surfactants were added to the shear-thickening fluid (STF) and their rheological properties were measured. The results indicated that all kinds of surfactants could enhance shear-thickening behavior by changing their electrostatic, steric, or lubrication interaction, especially for nonionic surfactant Triton X-100 (TX100) and cationic surfactant cetyltrimethyl ammonium bromide (CTAB). TX100 led to the maximum viscosity up to 1,650 Pa s and CTAB enhanced the maximum viscosity up to 1,000 Pa s when the introduced surfactants were only 2 and 0.3 %, both values were nearly five times larger than the neat STFs. A plausible explanation for the enhancing mechanism by different kinds of surfactants was discussed.