emulsions and creams 1

liquid emulsions for oral use are usually what type

o/w

what does the type of emulsion formed depend on?

phase volume ratio- larger volume phase is usually the continuous phase

which emulsion will conduct electricity?

o/w

In the dye test, which emulsion turns red and which turns pink?

W/O turns red, O/W turns pink

why are emulgents for o/w creams used in excess?

the excess emulgent gives structure to the continuous phase which enhances stability by increasing viscosity (rheological barrier), impeding the approach and coalescence of droplets.

how do emulgent systems create structure

by forming crystalline hydrates and/or swollen gel phase.

when an emulsion has a high surface free energy, what does that mean?

it is thermodynamically unstable

what are the types of physical instability of emulsions (5)

• creaming/sedimentation

• flocculation

• Ostwald ripening

• Coalescence/ cracking

• Phase inversion

explain the physical instability of creaming / sedimentation

Formation of a relatively concentrated emulsion at the surface (creaming) or bottom (sedimentation) of the emulsion. it is reversible- shaking the emulsion will restore it.

explain the physical instability of flocculation

Clustering of emulsion droplets – attracted to each other but remain separated by continuous phase. DLVO secondary minimum effect. reversible

explain the physical instability of Ostwald ripening

• only happens in a system of partially miscible liquids

• Growth of large droplets at the expense of small droplets

• droplets do not need to make contact with each other

• Irreversible

explain the physical instability of cracking / coalescence

• the merging or droplets to form larger droplets

• irreversible

what is phase inversion

when a w/o becomes an o/w

explain phase inversion

• may happen deliberately; as a change of water solubility of non-ionic surfactant with temp OR deliberate alteration of phase volume ratio

• may occur due to instability if the original phase volume ratio was too high or when an incompatible agent is added that changes the nature of the emulgent

• Irreversible

the presence of electrolytes can…

• reduce the energy of interaction between adjacent globules

• have a salting-out effect (high concentrations of electrolytes can strip emulsifying agents of their hydrated ayers and so cause their precipitation).

• phase inversion may occur, e.g. addition of divalent metal ion to a sodium soap (O/W) emulsion, will form divalent metal soap, which forms a w/o emulsion.

what are some disadvantages of oral emulsions

• Effective shaking before use required

• Stability affected by storage conditions

• Prone to microbial contamination may cause instability

what are the 3 types of fixed ratios for primary emulsions

1. fixed oil = 4,2,1

2. mineral oil= 3,2,1

3. volatile oil = 2,2,1

what is the difference between dry gum and wet gum method of creating emulsions