Colloids

=Colloids=

By Harv and Hammy
Colloids are the dividing line between homogeneous and heterogeneous mixtures. Their particles are not small enough to form homogeneous mixtures, but not big enough to form heterogeneous mixtures. Under a microscope colloids appear to be uniform but when light in shined through their properties are demonstrated. The particles are big enough to scatter light, so when light is shone through you can see a light beam. This is called the **Tyndall Effect**. This is the reason why you can see light shining through a forest canopy, or light-beams on a dusty road. Different wavelengths are reflected different ways, this is why sunsets can be different colors.



Colloids have two different phases and they are the dispersed phase (also known as the internal phase) and the continuous phase (or the dispersion medium). The dispersion phase is made up of a mixture of tiny particles ranging from 1 nm to 1000 nm evenly dispersed throughout the continuous phase. These dispersion phase particles are normally too small to see with a regular microscope and an electron microscope or ultra-microscope is therefore needed. Homogeneous mixtures with dispersion phases of this size are known as colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions, or hydrosols. Dispersion phase particles are mostly affected by the surface chemistry of the colloid.



A common trait of colloid with a solid phase dispersed in a liquid phase, the solid colloid particles will not pass through a membrane while the dissolved liquid will. Some common colloids are butter, milk, smoke, glue, and sea foam. Colloids can be a mix between any two phases except for a gas and a gas because gases are always miscible.



Table - http://en.wikipedia.org/wiki/Colloids

Hydrophilic and Hydrophobic Colloids
These are the most important colloids are the ones that use water as it's dispersion medium. Hydrophilic colloids can be in different states depending on the amount of water present. This then splits hydrophilic colloids into two groups: reversible and irreversible. Reversible colloids can change states with the addition or reduction of heat or pressure. Irreversible are unable to change forms.

Hydrophilic
Hydrophilic colloids are held in suspension by their interaction with water molecules. A good example of this is the enzyme and antibodies in our system, they stay floating in the blood stream by interacting with the water molecules. Gelatin is a hydrophilic colloid. Hydrophilic colloids are used in foods to mess around with texture or viscosity. Hydrophilic colloids are sometimes used in skin care products and wound treatment products.



Hydrophobic
This type of colloid can only be prepared in water if they are stabilized first. This have very little **affinity,** or attraction, to water. They can be stabilized by **adsorbing** ions to their surface. The ions interact with the water and other hydrophobic molecules keeping them separated. They can also adsorb hydrophilic molecules which will act the same way as the ions.

Works Cited:
Chemistry: The Central Science Wikipedia - en.wikipedia.org/wiki/colloids Pictures - cited under images