6. Gels and magmas Flashcards
What are gels?
Gels are defined as semisolid systems consisting of dispersions made up of either small inorganic particles or large organic molecules enclosing and interpenetrated by a liquid.
What is the appearance of gels?
Some gel systems are as clear as water, and others are turbid because the ingredients may not be completely molecularly dispersed (soluble or insoluble), or they may form aggregates, which disperse light.
What are single phase gels?
Gels in which the macromolecules are distributed so that no apparent boundaries exist between them and the liquid are called single-phase gels.
What are two phase gels?
When the gel mass consists of floccules of small, distinct particles, the gel is classified as a two phase system and frequently called a Magma or a Milk.
What are colloidal dispersions?
Gels and magmas are considered colloidal dispersions, because they contain particles of colloidal dimension (particles size between 1 nm and 0.5 micro-m.)
How are gels classified?
- Organic
- Inorganic
- Hydrogels
- Organogels
What are inorganic gels?
Usually two phased systems
Example of inorganic gels
Aluminium hydroxide gel
Bentonite magma
What are organic gels?
usually single-phase systems
Examples of organic gels?
Carbomer, tragacanth
What are hydrogels?
- organic hydrogels
- natural and synthetic gums
- inorganic hydrogels
Give examples of hydrogels
- pectin paste, tragacanth jelly,
- methycellulose, sodium carboxymethylcellulose
- Bentonite gel (10-25%), veegum, silica
What are organogels?
- Hydrocarbon type
- Animal, vegetable fat
- Soap base greases
- Hydrophilic organogels
Examples of organogels?
- Petrolatum, mineral oil/polyethylene gel (plastibase)
- Lard, cocoa butter
- Aluminium stearate with heavy mineral oil gel
- Carbowax bases (PEG ointment)
What is jelenes or plastibase
Jelene, or Plastibase :- a combination of mineral oils and heavy hydrocarbon waxes with a molecular weight of about 1300
What are carbowaxes?
the polyethylene glycols of high molecular weight.
What are carbowaxes?
a class of gels in which the structural matrix contains a high proportion of liquid, usually water
How are magmas and gels prepared?
Some magmas and gels (inorganic) are prepared by freshly precipitating the disperse phase to achieve a fine degree of subdivision of the particles and a gelatinous character to those particles.
As the microcrystalline particles of the precipitate develop, they strongly attract water to yield gelatinous particles, which combine to form the desired gelatinous precipitate
What are other methods of gel preparation?
Other magmas and gels may be prepared by directly hydrating the inorganic chemical, which produces the disperse phase of the dispersion.
What gelling agents other than water may be used?
In addition to the water, other agents as propylene glycol, and hydroxypropyl cellulose may be used to enhance gel formation.
What conc. of gelling agents is used?
The concentration of the gelling agents is mostly less than 10%, usually in 0.5% to 2.0% range.
Which are the gelling agents used?
Gelling agents include acacia, alginic acid, sodium alginate, bentonite, carbomer (carbopol), colloidal silicon dioxide, gelatin, magnesium aluminum silicate (veegum) , methylcellulose, polyvinyl alcohol (PVA), povidone, plastibase (Jelene) & tragacanth.
What are the examples of gels and magmas?
- Bentonite magma NF
- Aluminium Hydroxide gel USP
- Milk of magnesia
What is bentonite magma?
a preparation of 5% bentonite, a colloidal hydrated aluminum silicate, in purified water
