EXP 8 (POST LAB) Flashcards
When phases exist together, the boundary between two of them is termed an
interface
The properties of the molecules forming the interface are often sufficiently different from those in the bulk of each phase that they are referred to as forming an
interfacial phase
Several types of interface can exist, depending on whether the two adjacent phases are in the solid, liquid or gaseous state.
Interfacial Phenomena
is a property of liquids that results from the tendency of liquids to minimize their surface area
Surface Tension
The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules
Surface Tension
This “tension” of surface, is the
force per unit length
This force, the surface tension, has the units
dyne/cm in the cgs system.
Surface Tension
– caused by _____ of surface molecules
cohesion
Application of Interfacial Phenomena in Pharmacy
� To control the droplet size of pharmaceutical drops (e.g. ophthalmic solutions)
� Emulsion formation and stability
� Dispersion of insoluble particles in liquid media to form suspensions
� Dissolution of drugs
� Spreadability of topical preparations
Factors affecting surface tension:
� Temperature
� Presence of impurities
� Intermolecular force
� Density
� Viscosity
� Addition of surfactants
Is the force per unit length existing at the interface between two immiscible liquid phases
Interfacial tension
Interfacial tension
� Is the force per unit length existing at the interface between two immiscible liquid phases and like surface tension, has the units of
dyne/cm
are the molecules and ions that are adsorbed at interfaces.
Surface-active agents or surfactants
Surface-active agents or surfactants are the molecules and ions that are ____ at interfaces.
adsorbed
Surface-Active Agents
This is also known as ______, which the molecule or ion has the affinity for both polar and nonpolar solvents.
Amphiphile
In an amphipilic structure there are groups with opposite properties, one with the affinity to ____ and one with the affinity to___
water; lipids
Anionic surfactants:
❑ carries a negative charge such as R-COO−, RSO4−, or RSO3−
❑ most widely and extensively in detergents, shampoos, and body cleansers
❑ e.g. sodium dodecyl sulfate, sodium stearate, alkylpolyoxyethylene sulfate, triethanolamine oleate
carries a negative charge such as R-COO−, RSO4−, or RSO3−
Anionic surfactants:
most widely and extensively in detergents, shampoos, and body cleansers
Anionic surfactants:
e.g. sodium dodecyl sulfate, sodium stearate, alkylpolyoxyethylene sulfate, triethanolamine oleate
Anionic surfactants:
Cationic surfactants:
❑ have a cationic group, a functional group that can be positively charged at certain pH values.
❑ most are quaternary ammonium compounds
❑ used in fabric softeners and hair conditioners
❑ have antibacterial activity
❑ e.g. benzalkonium chloride, cetrimide, cetylpyridinium chloride
❑ have a cationic group, a functional group that can be positively charged at certain pH values.
Cationic surfactants:
❑ most are quaternary ammonium compounds
Cationic surfactants:
❑ used in fabric softeners and hair conditioners
Cationic surfactants:
❑ have antibacterial activity
Cationic surfactants:
e.g. benzalkonium chloride, cetrimide, cetylpyridinium chloride
Cationic surfactants:
Non-ionic surfactants:
❑ contain ether and/or hydroxyl [–OH] hydrophilic groups
❑ commonly used for stabilizing oil-in-water (o/w) and water-in-oil (w/o) emulsions.
❑ e.g. Spans
Tweens
❑ contain ether and/or hydroxyl [–OH] hydrophilic groups
Non-ionic surfactants:
❑ commonly used for stabilizing oil-in-water (o/w) and water-in-oil (w/o) emulsions.
Non-ionic surfactants:
❑ e.g. Spans
Tweens
Non-ionic surfactants:
