Preformulation Flashcards
What is an emulsion?
Metastable dispersion of liquid droplets in an immiscible liquid
What is a single emulsion?
A 2 component system- Liquid droplets in another liquid
e.g O/W emulsion or W/O emulsion
Disperse phase (droplets)
Continuous phase (liquid)
What is a double emulsion?
3 component system
Primary emulsion droplets in another liquid
W/O/W double emulsion
O/W/O double emulsion
What are colloids?
Multi-component dispersed phase systems where
the disperse phase is within the size range of 1–1000 nm.
Which type of emulsions are most common?
O/W emulsions
How do you make emulsion droplets last?
Emulsifier- form interfacial film around droplets, stabilise them by lowering interfacial energy
Viscosity enhancer- inhibit droplet diffusion, prevents coalescence (coming together)
Describe the stability of emulsions.
Emulsions are metastable
The droplets undergo Brownian motion and may interact with each other
Attraction promotes droplet consolidation and causes instability
Repulsion promotes droplet separation and causes stability
What does Bancroft’s rule say and what does this help to explain?
“The phase in which the emulsifier is more soluble is the continuous phase” (Like associate with like)
Hydrophilic emulsifiers produce O/W emulsions
Lipophilic emulsifiers produce W/O emulsions
Explains the type of emulsion that will be formed.
What are the 4 types of emulsion instability? and say whether they are reversible or irreversible.
Creaming (Reversible)- Where fat floats to the top
Sedimentation (Reversible)- fat floats to bottom
Cracking- Irreversible
Flocculation (Reversible), Coalescence (Irreversible)
-Flocculation come together but don’t merge
What is the DLVO theory?
Electrical repulsion- electrical double layer
Van der Waals attraction- induced dipole-dipole interactions
The attraction (VA) and repulsive (VR) change at different rates with different particle distance
The sum of these energies (VT) explains particle dispersion or flocculation
VT= VA + VR
What is sedimentation and what promotes it?
Particles (droplets) sink in the continuous phase under opposing forces
Promoted by:
Greater density difference
Lower fluid viscosity
What does the HLB number tell you?
HLB<10= More soluble in oil
HLB>10= More soluble in water
What is the HLB value for a W/O emulsifier?
3-6
What is the HLB value for an O/W emulsifier?
8-16
Define surface tension.
Energy required to expand the surface of a liquid by a unit area
Define surface energy.
Potential energy per unit surface area
What are the phase boundaries?
Interface- boundary between two phases
Surface- boundary between two phases, one of which is a gas
A surface is an interface, but not all interfaces are called surfaces
How does temperature affect surface tension for most liquids?
For most liquids, surface tension declines with increasing temperature
How can surface tension be determined?
Using the Wilhelmy plate method or the du Nouy ring method
How do surfactants affect surface tension?
Surfactants reduce surface tension
What does the correct angle mean?
Indicator of solid surface wettability
What does wettability mean?
Tendency of liquid to adhere to solid surface
What are some uses of surfactants?
Detergent, emulsifying agent, solubilising agent, wetting agent, foaming agent, flocculating agent
What is the critical micelle concentration (CMC)? How does the size of a surfactant molecule affect the CMC?
Minimum surfactant concentration at which micelles begin to form
Generally, the larger the surfactant molecule, the lower the molar CMC.
