3-10 Exam 14 Dispersed Systems Rheology

Front 1

What are pharmaceutical dispersed or two phase systems?

Back 1

Liquid dosage forms – containing underdissolved or immiscible drug distributed throughout a medium (vehicle or solvent).

All systems in thermodynamic equilibrium are disperse systems.

Front 2

What are types of two phase systems?

Back 2

Suspensions
Emulsions
Gels and magmas (or milks)

Front 3

Explain Colloidal systems

Back 3

i. generally applied to a heterogeneous mixture (two phase system)
ii. Particle size distinguishes colloidal systems from other material systems
iii. Example: gels and magmas

Front 4

Explain Coarse dispersion system

Back 4

i. Particles are greater than 1 micro meter in diameter
ii. Visible under microscope
iii. Pharmaceutical emulsuions and suspensions

Front 5

How are two phase systems formulated.

Back 5

Most need a perservative

Front 6

What are the main problems with multi-phase liquid dosage forms?

Back 6

Wetting
Particle Aggregation
Interfacial Phenomena

Front 7

Main points regarding wetting

Back 7

1. Wetting is the ability of solvent to spread itself on the surface
2. Wetting agents - are surfactants - increases the ability of molecule to spread out on a surface
3. Lubricants can be added (mg stearate and aluminum stearate was shown to decrease dissolution rate)

Front 8

What are the 2 main forces of wetting?

Back 8

Cohesive forces & Adhesive forces

Cohesive forces = liquid and liquid molecules

Adhesive forces between molecules of solid and liquid.

If adhesive forces are greater than cohesive forces, you get wetting.

Front 9

What is an example of a wetting agent?

Back 9

Sodium lauryl sulfate (a surfactant)

Wetability of tablet is also improved by natural surfactants such as bile acids in GI fluid

Front 10

Details of particle aggregation

Back 10

In suspensions, can have either flocculation or caking

In emulsions, settling and aggregation in emulsions may = phase separation (creaming)

Front 11

How can particle aggregation be prevented?

Back 11

If particles have a similar charge, aggregation can be prevented. Can manipulate via electrolytes, charged surfactants and charged polymers.

Front 12

What is Inferfacial phenomena?

Back 12

Properties of molecules situationed at or very near the boundary layer between immiscible phases.

Front 13

What is interfacial tension?

Back 13

Difference between forces on molecules at teh interface (boundry) and the bulk

Values of this tension = differences in chemical structure of 2 phases

Front 14

Examples of solutes used to reduce surface tension

Back 14

Surfactants, used for solubilizers, wetting agents, emulsifying agents.

Naturally occurring surfactants: (phospholipids, free fatty acids, bile salts)