Study Set Content:
It is a mixture containing air bubbles, fat globules, ice-crystals and and unfrozen serum phase
Ice- cream
Systems containing colloidal particles that interact to an
appreciable extent with the dispersion medium (solvent-loving)
colloids.
Lyophilic Colloids
Materials that have little attraction, if any, for the dispersion
medium (solvent—hating) colloids and, predictably, their
properties differ from those of the lyophilic colloids.
Lyophobic Colloids
Owing to their affinity for the dispersion medium, such materials
form colloidal dispersions, or sols, with relative ease.
Lyophilic Colloids
are usually obtained simply by dissolving
material in the solvent being used.
Lyophilic colloidal sols
Absence of a solvent sheath around the particle. Generally
composed of inorganic particles dispersed in water.
Lyophobic Colloids
Example/s: gold, silver, sulfur, arsenous sulfide, and silver
iodide.
Lyophobic Colloids
Most lyophilic colloids are organic molecule: gelatin, acacia,
insulin, albumin, rubber, and polystyrene. (Produce lyophilic
colloids in aqueous dispersion media (hydrophilic sols)
Lyophilic Colloids
Attraction between the dispersed phase and the dispersion
medium, which leads to solvation, the attachment of solvent
molecules to the molecule of the dispersed phase.
Lyophilic Colloids
In which water is the dispersion medium, this is termed
hydration.
• Hydrophilic Colloids
Special Methods to Prepare Lyophobic Colloids
Dispersion method
Condensation methods
In which coarse particles are reduced in size. Can be
achieved by the use of high-intensity ultrasonic generators
operating at frequencies in excess of 20,000 cycles per
second.
Dispersion method
In which materials of subcolloidal dimensions are caused to
aggregate into particle within colloidal size range.
Condensation methods
The required conditions for the formation of lyophobic colloids
by condensation or aggregation involve a high degree of initial
supersaturation followed by the formation and growth of
nuclei.
Can be brought about by change in solvent or reduction in
temperature.
Supersaturation
Example: Sulfur is dissolved in alcohol and the
concentrated solution is then poured into excess of water
many small nuclei form in the supersaturated solution.
Supersaturation
Are characterized by having two distinct regions of
opposing solution affinities within the same molecule or ion.
Amphipphiles or surface-active agents
When present in a liquid medium at low concentrations, the
amphiphiles exist separately and are of such a size as to
be
subcolloidal.
As the concentration is increased, aggregation occurs over
a
narrow concentration range.
These aggregates, which may contain 50 or more monomers,
are called
micelles
