Preformulation - surfactants Flashcards
What are the two phase boundaries?
- Interface: Boundary between two phases
- Surface: Boundary between two phases, one of which is a gas
What is surface energy?
- Surface energy: potential energy per unit surface area
- Spatial density of ‘unfulfilled bonds’.
- Intermolecular bonding stabilises molecules and lowers their energy.
Describe surface tension.
- Liquid-gas interface (surface).
- Apparent ‘film’ on liquid surface resists puncture.
- Liquid acquires minimal surface area, i.e. spherical droplet.
Define surface tension.
- Energy required to expand the surface of a liquid by a
unit area - For liquids, surface tension and surface energy are quantitatively equivalent
and often used interchangeably.
Describe the relationship between surface tension and temp.
- For most liquids, surface tension declines with increasing temperature
What do surfactants do?
Reduce surface tension
Define contact angle.
Indicator of solid
surface wettability
Define wettability
Tendency of liquid to adhere to solid surface
Describe an amphiphilic surfactant .
Has both hydrophilic and hydrophobic portions in the same molecule
State some uses of surfactants.
- Detergent
- Emulsifying agent
- Solubilising agent
- Wetting agent
- Foaming agent
- Flocculating agent
Describe micelle formation.
When the liquid surface is saturated with surfactant molecules, excess surfactant molecules sink below the liquid surface and self-aggregate into micelles.
What is critical micelle concentration?
Minimum surfactant concentration at which micelles begin to form.
Generally, the larger the surfactant molecule, the lower the molar CMC.
State traube’s rule?
- Molar concentration of surfactant needed to achieve a certain surface tension
decreases by ~3 fold with each —CH2 unit within a homologous series.
