Colloid Stabilisation Flashcards
Creaming of an emulsion or sedimentation of a
given suspension can be reduced in? give 3
1.by forming smaller particles
2.by increasing the viscosity of the continuous phase
3.by decreasing the density difference between the
two phases.
Why colloidal dispersion is thermodynamically unstable?
they have tendency to separate and reduce the interfacial area,hence interfacial energy
What is the effect of droplet size on colloid stability?
When the radius of droplet increases, the tendency to aggregate increases
What is the effect of viscosity on colloid stability?
when the viscosity of dispersion medium increases, the sedimentation rate of an emulsion decreases
What DVLO theory trying to state?
The colloidal stability is determined by potential energy of van der waals force(attraction) and repulsive electrostatic interaction
V total = V attract + V repulse
What happen to half-life of emulsion when energy barrier is increases?
increases
How dispersed phase acquire surface charge when disperse in aqueous phase?
- adsorption of ionic species present in aqueous phase
2. presence of charge on f.g. of dispersed phase e.g. COOH, NH2
low zeta potential(0-5mV) are prone to rapid aggregation while zeta potential >30mV would remain dispersed . T/F
T
How to alter zeta potential of dispersed phase?
Altering conc of ions in solution. the higher the ion concentration, the lower the zeta potential,increase tendency to aggregation
How steric stabilisation works?
when the particles with the anchored long-chain molecules (particle with brushes surrounding) approach each other,steric interaction occur when the layers overlap,cause repulsion
steric stabilization can stabilize a colloid even in the absence of a significant zeta potential . T/F
T
Dispersions experiencing steric stabilisation rely on zeta potential.
T/F
F
In steric stabilisation, what are the properties the polymer must have to adsorb to the surface of dispersed droplet?
surfactant properties
As the distance between two particles with diameter 1 µm decreases,
Select one:
the thickness of the electrical double layer increases.
attractive potential increases.
the Stern layer is shifted closer to the particle surface.
flocculation is unavoidable.
attractive potential increases.
