Dispersed Systems: Colloids

Solutions are known as in which the size of the internal phase is .

Molecular dispersions can pass through and semi-permeable membranes. They undergo rapid and are invisible under an .

Most pharmaceutical suspensions and emulsions are dispersions in which the size of the internal phase is .

Coarse dispersions are visible under a and do not . Particles can be separated via .

Colloids are also known as . Examples of colloids include and .

Colloids are dispersed systems in which the size of the internal phase is between and .

Colloids are visible through , they diffuse , and are separated by ultrafiltration or

Particle shape of colloids will depend on the phase of the medium. This will affect the .

There are three different classifications of colloids:
1. colloids
2. colloids
3 colloids

Lyophilic colloids:
molecules capable of being or with the molecules of the continuous phase. (example: acacia or gelatin)

Lyophilic colloids are prepared by . They are thermodynamically and reconstitution is possible.

Lyophilic colloids the viscosity of the medium and has two different phases the gel and solution phase

The solution-gel transition in a lyophilic colloid is dependent on the and

are thermodynamically unstable and reconstitution is not possible.

Lyophobic colloids require stabilization to prevent .

colloids are amphiphilic compounds such as micelles and vesicles.

Colloidal dosage forms include:
A)
B)
C) systems

A gel is a solid or semisolid system of at least two constituents:
a enclosing or interpenetrated by

: when liquid is present.

: When liquid is removed from a gel
and only the framework remains.
Examples include gelatin sheets, tragacant
ribbons, and acacia tears.

: Taking up liquid without a change in size

: Taking up liquid with a change in size

: Loss of liquid

Gels: One phase systems
- bond together with van der Waals forces to form or regions
(Ex. tragacant and carboxymethylcellulose)

Gels: Two phase systems
- of small particles form and create a network
- Not always stable
-
- Examples of this are aluminum hydroxide gel, bentonite magma, and magnesium magma

In gels, two phase systems are usually and single phase systems are usually ,

Examples of : Pectin paste, tragacanth jelly, and methylcellulose

Examples of : Petrolatum, mineral oil/polyethylene gel, and cocoabutter

With the acrylic acid-based polymer , maximum viscosity will happen at pH .

Carbomers
Are very , so should be kept in tight containers before use, or
they will get sticky.

A commonly used gelling agent known as is taken from seaweed. It needs to form the gel.

A commonly used gelling agent known as slowly hydrates in hot water and is then stirred with cold water to prompt dissolution

A commonly used gelling agent known as hydrates and swells in cold water. It makes thinner gels that are compatible with water and alcohol.

A commonly used gelling agent known as hydrates and swells in water and hydroalcoholic solvents. Good for high amount of drugs and makes thin gels.

The only true example of an organogel is or . This gel can be heated to about 60 degrees without loss of consistency.

gel is an antacid and may cause constipation. May interfere with the bioavailability of by .

is an antacid with anti-constipating effects. It does not cause constipation.

Gels should be kept in tight containers and should be observed for:
-
- Separation of liquid
-
-

If the particle size in a two-phase system is large, the gel is referred to as a

are thermodynamically stable, optically transparent mixtures of a biphasic o/w or w/o system stabilized with .

Microemulsions are prepared using surfactants with an HLB range of - such as polysorbate 60 and 80

Microemulsions are swollen micelles. The surface area is very in these microemulsions, therefore has become very low.

Microemulsions are used to enhance , as well as targetting anticancer agents

are used to provide sustained release of some drugs. Provides drug solubilization and protection, sustained and controlled release, , and drug internalization.

Depending on the process used for their preparation, two types of nanoparticles can be formed.
-
-

Nanocapsules coats the drug in a manner that is similar to that of an
Nanoparticles have drug dispersed throughout similar to that of a

are better for encapsulating hydrophobic drugs than liposomes because they can leak

:
Scattering may be described in terms of Turbidity which is the fraction decrease in light intensity due to scattering to all directions.

Bigger particles = diffusion coefficient = rate of diffusion