Effect of Surface Roughness on the Rheology of Silica-Coated Styrene/Acrylic Acid Copolymer Suspensions

Hypothesis: 

Today, due to the widespread use of coarse particle suspensions in chemical industry, the tendency to study the rheological behaviour of suspensions has increased significantly. One of the most important research fields is the study on friction of particles between them and the shear thickening behavior of their suspensions. In high-filled suspensions, the viscosity and the thickness of shear are proportional to the thickness of the suspended particles. 

This research is based on the syntheses of smooth particles (styrene/acrylic acid copolymers) and rough particles (silica-coated styrene/acrylic acid copolymers), with a volume proportion of 20%, 34% and 49% in the ethanol/water solution. The initial critical shear rate of suspension thickening regions was obtained in different ratios of rough and smooth particles. In addition, experimental and semi-empiric models such as Herschel Barclay and Gopalakrishnan have been used to describe the relationship between suspension rheology and microstructure. 

 It was observed that with the increase in roughness of the composition of the same percentage of particles, a more severe shear thickening behavior occurs in smaller amounts of rough particles. It was also observed that hydro-clusters were formed in samples that contain the highest proportion of suspension composition and consist of 100% coarse particles with the lowest amount of Peclet.  An increase in the amount of rough particles leads the system to an increase in viscosity at lower shear rates. Furthermore, the adaptation of the Gopalakrishnan model to experimental data clearly shows that an increase in roughness leads to a reduction in the critical value of Pe at the beginning of the shear thickening zone and a stronger shear thickness behavior in the system.