Surfactants are oragnic compounds which lowers the surface tension of a liquid, interfacial tension between two liquids or between a solid and a liquid. Surfactants are amphiphilic nature. In some conditions Surfactant acts as solubulizing agent, emulsifying agent, foaming agent, wetting agent and detergent. Surfacants contain two parts Head and Tail.
                                                              Head – Hydrophilic part (Polar)
                                                              Tail –   Hydrophobic part (Non-Polar)


Based on charge surfactants classified into three types…
1. Anionic sueractants
2. Cationic surfactants
3. Non-ionic surfactants

Anionic surfactants:

These are ionized in water to give large anionic group which is responsible for it’s emulsifying activity. 
Alkali metals or ammonium soaps: These are sodiumm, potassium, ammonium salts of fattyacids like Stearic acid, Palmitic acid, Ricinoleic acid etc…
These Produce o/w type emusions. 
Incompatible with poly valent cations leading to phase resversal.
Do not use in Oral preparation because produces irritation.
Soaps of divalent and trivalent metals: Magnesium, Zinc, Calcium salts of fatty acids produces only w/o type of emulsions.
These are used in zinc cream, oily calamine lotion.
Amine soaps: Triethanolamine stearate, Palmitate
Alkyl sulphates: Sodium lauryl sulphate(SLS)
                           Sodium cetostearyl sulphate

Cationic surfactants:

Cationic surfactants produce poor o/w emulsion. Used only for antiseptic formulations. These are incompatible with anionic surfactant, Polyvalent anions and unstable at high PH.
Preparations containing cationic surfactant does not require preservatives.
 Example: Cetrimide, Benzalkonium chloride

Non-Ionic Surfactants:

Non-ionic surfactants are absorbed at o/w interface forming a film in which the liphophilic and hydrophilic groups are directed towards oil and water respectively.
The hydrophilic surfactants has carboxy, hydroxy, amino group with affinity to water and form o/w type emulsion.
Example: Glyceryl mono stearate
The hydrophobic surfactants has long hydrocarbon with little affinity to water and form w/o type emulsion.
Example: polyethylene glycol derivatives


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