Emulsion and Suspension Stability (3)Physical Forces that Govern Stability Recap

Question 1

What particles are subject to Brownian Motion?

Answer 1

Particles less than about 2 microns in diameter, constantly moving due to BM

Question 2

What factors affect BM / kinetic energy?

Answer 2

Temperature and external forces such as shaking

Question 3

As particles approach one another what forces do they experience?

Answer 3

Forces of repulsion due to electrostatic interactions (Vr)
Forces of attraction due to VDW forces (Va)
Steric forces if they have a non-ionic surfactant on their surfaces (Energy of steric interactions (hinderance) =Vs
These energies combine to give total overall potential energy

Question 4

What is the primary minimum?

Answer 4

Permanent aggregation of particles when attraction is maximum and repulsion is minimum

Question 5

What is the primary maximum?

Answer 5

Repulsive barrier to aggregation when attraction is moderate and repulsion is moderate
Stable suspension / emulsion

Question 6

What is the secondary minimum?

Answer 6

Repulsion is minimal, attraction is weak but enough to cause flocculation