Course Dispersion

System

a bounded space of an exact quantity of a material

Dispersion

consists of at least two phases with one or more dispersed phase (internal) contained in a single continuous (external) phase

Phase

distinct homogenous part of a system (can identify 2 phases)

MOLECULAR DISPERSION

diameter of particles < 1 nm

-A.k.a. True Solutions (one-phase)

Dispersed phase: Nutrients

COLLOIDAL DISPERSION

- diameter of particles 1 to 500 nm

-e.g. gelatin mixture, milk

Dispersed phase: Serum albumin

COARSE DISPERSION

diameter of particles > 500 nm

- Ex. Emulsions and suspensions

•Dispersed phase: RBC

Blood

A Complex Dispersed System

•Dispersion medium: Plasma (90% water)

Pharmaceutical Suspension

•Dispersed Phase: Insoluble Solid

•Dispersed Medium:- Liquid

drug is not dissolved, but finely divided and suspended in the vehicle.

Particle size

Ideally in the range of 1-10 μm. Finer particles improve uniformity but may cake.

Sedimentation rate

Described by Stokes' Law. Affected by particle size, density, and viscosity of the medium.

Redispersibility

The ability to resuspend sedimented particles with mild shaking

Flocculation

suspensions form loose aggregates (easier to redisperse)

deflocculated

particles settle compactly.

Viscosity

Should be high enough to reduce sedimentation, but low enough to pour or inject easily.

Zeta potential

Surface charge that influences particle repulsion/attraction and suspension stability. Stable suspensions: values < -25mV or >+25mV

Appearance

Should be uniform, elegant, and free from caking, grittiness, or phase separation.

Palatability

For oral suspensions, taste and mouthfeel are important (may require sweeteners, flavoring, etc.)

Dilute Suspension

Free Settling

5% Suspension

Hindered Settling

Larger particles

settle more rapidly.

SUBSIDENCE

• Settling in flocculated systems

Structured suspensions

• Use suspending agents like xanthan gum, tragacanth, or carboxymethylcellulose to prevent settling by increasing viscosity.

Unstructured suspensions

• No structured vehicle; rely on other factors (e.g., particle size, density difference) to reduce sedimentation.

oral

5 - 50%

Antacids, antibiotics (e.g., amoxicillin)

Parenteral

0.5 – 25%

Injectable corticosteroids

Topical

5 - 50%

Antipruritics, anti-inflammatory lotions

Ophthalmic

0.1 – 1%

Anti-inflammatory eye drops

O/W (Oil in Water)

Oil droplets in water; external phase is water

Oral or injectable emulsions

W/O (Water in Oil)

Water droplets in oil; external phase is oil

Topical emulsions/ointments

Multiple Emulsions

W/O/W or O/W/O; complex structure

Controlled-release systems

Microemulsions (micellar emulsions)

Thermodynamically stable, clear, nanosized emulsions

Intravenous or transdermal delivery

Creaming

droplets migrate to the top (or bottom) due to density differences

Coalescence

small droplets merge into larger ones

Cracking/Breaking

complete separation into two distinct liquid phases.

Phase Inversion

from O/W to W/O or vice versa

Viscosity

Depends on phase volume ratio and emulsifier used

O/W emulsions

usually milky Appearance

Dilution Test

The emulsion will mix freely with the liquid that forms its external (continuous) phase.

- Miscible → O/W emulsion - Not Miscible → W/O emulsion

Dye Test

Add a water-soluble dye (e.g., methylene blue) to the emulsion.

- Continuous phase is colored → O/W emulsion - Droplets are stained → W/O emulsion

Fluorescence Test

Examine under UV light (many oils fluoresce, while water does not).

- Continuous phase fluoresces → W/O emulsion - Discontinuous spots fluoresce → O/W emulsion

Conductivity Test

Test the ability of the emulsion to conduct electricity (water conducts, oil does not).

- Conductive → O/W emulsion - Non-conductive → W/O emulsion