Colloids Flashcards
What are colloids?
Dispersions of particels sized between 1nm - 1 microm (tiny)
What happens because they are so small?
They are less likely to be affected by gravity.
What are the three types of colloids?
Lyophobic
Lyophilic
Amphiphilic
What is a lyophobic colloid?
Solvent/liquid hating. Particels have a different polarity to the dispersant. They are thermodynamically unstable and will not stay in this state naturally. The particles will aggregate to try to lower their surface area and energy, to try to seperate from th solvent as much as possible. They will therefore clump together.
e.g. oils, inorganic particels in water
What is a lyophilic colloid?
Solvent/liquid loving
These particels will have an affinity for the solvent i.e. will have similar polarity. The particels and solvent will interact leading to solvation. There is no coaggulation due to the protective dispersant ‘coat’. The dispersion is stable e.g. proteins
What is an Amphiphilic colloid?
lyophilic and lyophobic = liquid loving and hating.
These are particles with regions that have different affinities for different dispersants. They will oriantate at the surface to allow each region to be in contact with its preferred phase. If the surface becomes full, the particels will form spherical MICELLES. to stay in contact with preferred phase.
if water is the solvent of a lyophilic colloid, what is the process of particels interacting with the water called?
Hydration
What dictates if particles rebound, temporarily bind or permanently bind in a colloid?
The balance of forces between the particles i.e. Attractive, Repulsive, or solvation forces.
What forces exist in Lyophobic and Lyophilic colloids?
Attractive or Repulsive forces
What forces exist in Lyophilic colloids only?
Solvation forces due to the dispersant ‘coat’ that makes the particels less likely to attach.
What is the concept of ‘salting out’?
Why would salting out be used?
This is adding electrolytes to the system of a Lyophilic colloid.
Salting out would be used to seperate the dispersed particles from the solvent in a lyophilic system
How does salting out work?
Normal in lyophilic colloids, the particles have solvation forces due to the dispersant ‘coat’ around each particle, therefre preventing the particles from aggregating.
Adding some electrolytes will cause some neutralisation of particels by pulling the solvent particels off by difusion, but there is still enough Dispersant coat to prevent aggregation.
Adding lots of electrolytes will cause more of the dispersant coat to come off, and the particels can not aggregate and fall out of solvation.
WHat would happen to a lyophobic colloid if electrolytes were added?
A lyophobic colloid’s stability is more affected by electrolytes because the stability relies entirely on charges. There is no dispersant coat in lyophobic colloids.
Without electrolytes, the particels repell each other,
Adding electrolytes e.g. as a floavouring agent will cause the particles to become neutral over all, and won’t repell each other, will aggregate and sediment.
Wy do different lyophilic colloids require different concnetrations of electrolytes to casue salting out?
Different lyophilic colloids require different concnetrations of electrolytes to cause salting out because of different degrees of solvation.
High degree of solvation = higher electrolyte concentration required for salting out because of a strong dispersant coat.
How would we seperate two different types of particels from a lyophilic colloid?
Add enough electrolytes to cause the particle with the weakest disoersant coat to aggregate, leaving the particels with the strong dispersant coat still dispersed.
