Electrostatic stabilization

Question 1

What are polyelectrolytes?

Answer 1

~ polymers with an ionizable group

~ effective at forming concentration (>50%) deflocculated suspensions

Question 2

What are examples of polyelectrolytes?

Answer 2

~ PMAA and PAA (Darvan)

~ both have a carboxylic acid functional group (COOH) that can dissociate in aqueous solution: A-COOH + H2O –> A-COO- + H3O+

Question 3

What effects the extent of ionization?

Answer 3

~ ionization increases with increasing pH (lower H3O+ conc.)

Question 4

What happens at high pH?

Answer 4

~ the polymer forms highly open coils because of mutual electrostatic repulsion of polymer chains

Question 5

When is adsorption of polyelectrolyte onto particle surfaces highly favored?

Answer 5

~ if they are of opposite charge

Question 6

What is the isoelectric point of alumina? What effect does this have on PMAA-Na?

Answer 6

~ 8.5

~ PMAA-Na (H in COOH is replaced by Na+) should be attracted to the surface at pH values BELOW 8.5

Question 7

What happens at a lower pH?

Answer 7

~ the more polymer adsorption onto the surface

~ the more compressed the polymer

Question 8

What is the effects of vaying particle separation?

Answer 8

~ larger particle separation: electerostatic repulsion dominates
~ smaller particle separation: steric repulsion is more pronounced