Preformulation - Surfactants Flashcards
What is a surfactant?
Surface + active + agent
What is an interface?
Boundary between 2 phases
What is a surface?
Boundary between 2 phases, one of which is a gas
Is a surface an interface?
YES
Are all interfaces surfaces?
NO
What is surface energy?
Potential energy per unit SA
What do surfactants do?
Reduce surface tension
Describe surface tension
Apparent “film” on liquid surface that resists puncture
What interface is surface tension?
Liquid-gas interface
What does liquid acquire?
Minimal SA
Describe surface energy
Intermolecular bonding stabilises molecules + lowers their energy
What does surface energy do?
Net inward force exerted on “like” molecules on liquid by bulk
What do surface molecules not have?
No “like” neighbours above surface for bonding
What is surface tension?
Energy required to expand surface of a liquid by a unit area
For most liquids, what happens to surface tension as temperature increases?
Decreases
How do you measure surface tension?
Ring/plate placed in H2O till breaks water surface
Attached to hook that measures force
What is the contact angle?
Angle liquid makes contact with surface
What is the contact angle an indicator of?
Solid surface wettability
What does it mean if there is a smaller contact angle?
More wetter surface by liquid
What is wettability?
Tendency of liquid to adhere to solid surface
What is amphiphilic?
Has both hydrophilic + hydrophobic portions in same molecule
eg. surfactants
What is the contact angle equation?
ɣsg - ɣsl - ɣlg COSθ
ɣsg = solid + gas ɣsl = solid + liquid ɣlg = liquid + gas
What are the uses of surfactants?
Detergents Emulsifying agent Solubilising agent Wetting agent Foaming agent Flocculating agent
What does the hydrophilic part do?
Interact with H2O surface
What does the hydrophobic part do?
Try to get away
What happens when a liquid’s surface is saturated with surfactant molecules?
Excess surfactant molecules sink below liquid surface + self-aggregate into micelles
What is the Critical Micelle Conc (CMC)?
Minimum surfactant conc at which micelles begin to form
What happens to the CMC if there is a larger surfactant molecule?
Lower it is
What is Traube’s Rule?
Molar conc of surfactants needed to achieve a certain surface tension decrease by 3 fold with each -CH2 unit within the homologous series
