Lecture 2 Flashcards
What is a cosmetic?
Product, except soap, intended to be applied to the human body for cleansing, beautifying, promoting attractiveness or altering the appearance.
When is cosmetic also a drug?
When it is intended to cleanse, beautify, or promote attractiveness as well as treat or prevent disease or otherwise affect the structure or any function of the human body.
Emulsion
A system of two of more immiscible materials in which one material is suspended/dispersed throughout the other material in separate droplets.
How does an emulsifier work?
Reduces the interfacial tension between the dispersed and continuous phases. Can be liquid, polymer or solid.
Characteristics of o/w emulsion
Stable pH
Can be diluted with water (lowering the viscosity)
Can be washed off skin with water
Will exhibit conductivity
Characteristics of w/o emulsion
Unstable pH
Will feel heavy and greasy
Can be diluted with oil
Cannot be readily washed off the skin
Bancroft’s Rule
Whichever phase the surfactant is most soluble in, is the continuous phase.
Van’t Hoff’s Rule
the velocity of chemical reactions is increased twofold or more for each rise of 10°C in temperature
Aggregation/Flocculation
particles approach each other (reversible)
Coalescence
particles approach each other and their films rupture (irreversible)
To prevent coalescence:
Steric and or electric barriers to keep droplets apart. This can be done by surfactant choice and viscosity enhancement.
Mechanism of Stabilization
A barrier forms around the emulsion droplets and strengthens the o/w interface. A gel network is then formed.
What are emulsifying “wax” systems?
Mixtures of hydrophilic and lipophilic emulsifiers, usually nonionic. These lead to “one step” emulsification, which are popular in high pH systems.
Characteristics of emulsifiers
Longer, hydrophobic chains with less branching and less unsaturation. There may be nonionic, anionic, or cationic headgroups. Mixtures are more efficient and effective, and particles can also stabilize an emulsion.
