Question

Discuss how the viscosity of an Al2O3 suspension would change depending on the order in which poly (acrylic acid) and poly (vinyl alcohol) are added to the suspension.

Answer 1

The viscosity of an Al₂O₃ suspension decreases as the poly (acrylic acid) concentration increases when it is added to the suspension .
At some critical poly (acrylic acid) concentration which corresponds to the amount required to form a complete monolayer on the particle surface and thus at low plateau region where it is independent of poly (acrylic acid) concentration this change in viscosity reflects the change from the flocculated suspension at low poly (acrylic acid) concentration to an electrosterically stabilized system at above the critical poly (acrylic acid) concentration. After the critical concentration is reached further addition of the in which poly (acrylic acid) means to produce polymer in the solution and viscosity of suspension starts to increase again at higher concentration.

Upto the critical point viscosity is same as poly (acrylic acid) but as the concentration of poly (vinyl alcohol) ​ increases the vicosity increase and also when poly (vinyl alcohol) added to the suspension adsorption process takes place as its concentration increases thus the particle surface became more saturated and a plateau region occur in adsorption isotherm. Further increases in concentration woluld lead to the second plateau region to occur in the adsorption isotherm it's due to the development of denser packing in the adsorbed polymer.