Dispersion Interfaces and Amphiphilic Molecules + DLVO Theory and the Gibbs-Marangoni-Effect

Question 1

What role do amphiphilic molecules play in dispersions?

Answer 1

Amphiphilic molecules (surfactants) reduce interfacial tension, stabilize emulsions, and slow down processes like Ostwald’s ripening by balancing hydrophobic and hydrophilic interactions.

Question 2

What is the significance of the HLB (Hydrophilic-Lipophilic Balance) value in emulsifier selection?

Answer 2

HLB values help determine the suitability of an emulsifier for a specific emulsion type; values of 8-16 are ideal for oil-in-water emulsions, while 3-6 are suitable for water-in-oil emulsions.

Question 3

Explain the Gibbs-Marangoni effect.

Answer 3

The Gibbs-Marangoni effect is the mass transfer along an interface due to a surface tension gradient, leading to the redistribution of emulsifiers and stabilizing the droplets by pushing them apart (repulsion)

Question 4

Describe the DLVO theory in relation to dispersion stability.

Answer 4

DLVO theory explains the balance of van der Waals attraction and electrostatic repulsion between charged droplets in a continuous phase, influencing their stability and potential for aggregation.

Question 5

What can occur if an incorrect HLB value is selected for an emulsion?

Answer 5

Selecting an incorrect HLB value can lead to phase inversion, destabilizing the emulsion and causing undesirable separation of phases.