EFFECTS+OF+IONIC+STRENGTH+AND+pH+IN+COLLOIDAL+PARTICLES

this is my first time writing in wiki..haha okay, my part is the effects of ionic strength and pH in colloidal particles... in my opinion, before mastering this part, we should know the DLVO theory first because from there it applies to all this small subtopic.. before i go into details,i think we should know some terms first:

1) **electrostatically stabilized emulsion** --> involved with charged surfactant that usually anionics. when forming an aqueous solution (put into water) the ionic surfactant will breaks into 2 components; the anionic surfactant portion and the cationic counterion. we can imagine this in an example when NaCl is dissolved in water (correct me if i'm wrong). This is called IONIZATION. in the presence of a suspended oil phase, the hydrophobic tails of the anionic portion are 'dissolved' in the oil droplets leaving the charged heads on the droplet surface. this molecular orientation results in a net negative charge on the surface of the droplet. this surface charge leads to the formation of a secondary shell of dissolved countering which is positively charged. the negative surface or the positive secondary shell system is known as an ELECTRICAL DOUBLE LAYER. the end resultof the double layer emulsion stabilization as two approaching oil droplets are barred from coalescing by their mutually repulsive positively charged outer shells.

2) **isoelectric point(pI)** -->the pH at which protein carries no net charge above pI: protein carries net -ve charge Okay enough with the terms ya… __EFFECTS OF IONIC STRENGTH AND pH IN COLLOIDAL PARTICLES__  The thickness of the electrical double layer or counterions around the charged particles surface is compressed by the salt and hydrogen ion concentration. In such a degree, the salt and hydrogen ion could make the repulsive force inaffective in stabilizing the emulsion. When the repulsive force is inaffective in the system, the particles will flock together making the emulsion unstable. In other words, low salt~ stability increases; high salt ~ flocculation increases. AS LONG AS IONIC STRENGTH IS LOW, ELECTRICAL REPULSION IS GREATER THAN VAN DER WAALS ATTRACTION, therefore the droplets REMAIN SUSPENDED  Electrostatically stabilized emulsions are sensitive towards ionic strength and pH of the aqueous phase. In the electrostatically stabilized emulsion consist the electrical charge of many food emulsifiers. We know that almost all food contain proteins. Isoelectric point plays an important role in determining the condition of the food. For example, the droplet charge of protein-stabilized emulsion decrease as the pH is approaching the isoelectric point of proteins. This will reduces the magnitude of the electrostatic repulsion between the droplets. Therefore, the tendency of the protein-stabilized emulsion to become aggregate increases as the pH tends towards the isoelectric point.
 * 1) below pI: protein carries net +ve charge
 * 1) significant in protein purification because it is the pH at which solubility is often minimal and at which mobility in an electrofocusing system is zero (point where protein will accumulate).