Interfacial Phenomena Flashcards
What is an interface?
a boundary between phases
What do interfacial phenomena affect?
4
- absorption onto solid adjuncts
- penetration through biological membranes
- emulsion formulation
- dispersion (suspensions)
Interfacial/surface tension definition
the force that must be applied parallel to the surface to counteract the net inward pull
dyne/cm
Interfacial tension
liquid-liquid interfaces
Surface tension
liquid-vapor or solid-vapor interfaces
Surface free energy
work done in increasing the surface area
cohesion
attraction between like substances
adhesion
attraction between unlike substances
Meaning of spreading coefficient
positive: spreading occurs (free energy of new surface interface is lower than free energy of old surface)
negative: spreading does not occur
L2 = gamma D t / 4 n
cookie dunking optimization
When do we use spreading coefficients in pharmacy?
3
- topicals
- emulsions
- other liquids
Positive adsorption
molecules move toward the surface interface
Negative adsorption
molecules move toward the bulk
Where are surface active agents used in pharmacy?
3
- emulsions
- suspensions
- foams
oil in water (o/w) emulsion examples
Noxema, Eucerin
water in oil (w/o) emulsion examples
Lanolin, Nivea
Hydrophile-lipophile balance (HLB)
describes surfactants (higher –> hydrophilic)
one surfactant’s HLB should be higher and one surfactant’s HLB should be lower than the RHLB (required HLB)
Pharmaceutical relevance of solid-liquid adsorption?
2
- tablet wetting
2. activated charcoal for overdoses
What is the most important action of a wetting agent?
lowering the contact angle
Wettability of tablet surfaces influences what?
3
- disintegration
- dissolution
- subsequent release
lower contact angle, higher work of adhesion –> better wetting
:)
Where are surfactants used in pharmacy?
5
- emulsions
- suspensions
- creams/ointments/lotions
- antibacterials (are themselves a drug agent)
- aid absorption
