Elizabeth-Food+colloids

__FOOD COLLOIDS__

Colloidal dispersion ( SOL)---> dispersions of two or more immiscible materials. Simplest coloidal system---> single dispersed phase in second continuous phase.

Example in this picture, the yellow colour particle is the dispersed phase, and blue solution is the continuous phase.

Suspension--> any system contain particles which is >1micro meter, and prone to settle under gravity Emulsion--> dispersion or suspension of liquid droplets in a liquid continuous phase Foam--> Coarse dispersion of gas bubbles in liquid continuous phase

Polydispersity can be monodisperse and polydisperse picture of monodisperse phase ( all uniform and same size)

Picture of polydisperse ( not uniform in sizes)

__ Interactions between dispersed droplets __
The interacting forces in affecting colloidal systems are --> Van der Waals attractive forces and electrostatic repulsive forces

These forces can destabilize colloids whereas repulsive forces will impart stability

**__Van der waals interactive forces__**



 * Originate from dipole-dipole interactions
 * Force between 2 droplets arising from van der waals forces always attractive for like droplets
 * Attractive forces increase more as the droplets approach

__**Electrical double layer**__

 * Oppositely charged ions(counterions) attracted towards the surface, ions of the same charge(coions) will repelled away
 * Electrical double layer is the combination of charged surface and the unequal distribution of coions and counterions near the surface
 * Important for colloid stability
 * Double layer sensitive to electrolytes and temperature

**__Electrostatic forces and DLVO theory__**
DLVO--> name of 4 scientists--> Derjaguin, Landau, Verwey, Overbeek DLVO suggest--> electrical double layer repulsion will stabilize emulsion, when electrolyte concentration phase less than a certain value Stability of emulsified droplets to two independent potentials that come into action when two droplets approach each other Small distance, sum of 2 energies always negative( cause aggregation) Sum of 2 energies always positive ( cause repulsive force)

__ Surface and interfacial tension __
Surface tension--> Property of liquid in contact with air that makes it behave as if it covered with a thin membrane under tension

These photos show the surface tension acting on the water, in water droplets from the flower, and the water strider can walk on water because of the surface tension.

This photo show the molecule inside the liquid interact equally with other molecules from all sides, molecules on the surface only affected by the molecules below it.
 * Surface tension also defined as force acting over the surface of the liquid per unit length of the surface perpendicular to the force.

Very important quality of colloids. The decrease in size means increase number of particles, this will increase the area of interfacial contact.
 * __Large interfacial area__ **