13. Colloidal Stability

Question 1

As two charged particles in a fluid approach, ions in the fluid move to maintain _________ _________.

Answer 1

Electrical neutrality

Question 2

Give the equation for potential decay between two charged plates in an electrolyte

Answer 2

V(x) = potential
V0 = initial potential
1/κ = Debye screening length
x = position

Question 3

Give the equation for the Debye screening length

Answer 3

1/κ = Debye screening length
ε = permittivity
kB = Boltzmann’s constant
T = temperature
n0 = number density of particles far from gap
z = atomic number
e = electron charge

Question 4

What is the Debye screening length?

Answer 4

The distance over which a charged particle’s potential can be felt

Question 5

What is the electrostatic screening of particles affected by?

Answer 5

The concentration of ionic charges in solution (the greater the concentration of ions, the shorter the screening length).

Question 6

Is osmotic pressure attractive or repulsive?

Answer 6

Repulsive

Question 7

Give the equation for osmotic pressure in the gap between two charged surfaces in terms of the Debye screening length

Answer 7

Π = osmotic pressure
n0 = number density of particles far from gap
z = atomic number
e = electron charge
V0 = initial potential
kB = Boltzmann’s constant
T = temperature
1/κ = Debye screening length
D = separation between two charged surfaces

Question 8

Give the equation for the total pressure between two charged surfaces

Answer 8

Question 9

What does the total pressure between two charged surfaces determine?

Answer 9

Whether particles come together and stick or stay separate in suspension.