IN this series of critical views,I had already dealt with Dispersion and let me go over to Wetting & Surfactant actions.The idea to deal with these subjects again in a different form is to give more insight to the readers,so that they are able to appreciate the technology well and make better quality paints.These toplcs will give them more insight on the subjects.Readers may find that some part of the subject is repetitive,but here they are dealt with differently and in detail than before Surfactants are compounds that lower the surface tension(or interfacial tension)between two liquids,between a gas and a liquid,or between a liquid and asolid.Surfactants may act as detergents,wetting agents,emulsifiers,foaming agents,and dispersants.Wetting agents are substances that reduce the surface tension of water to allow it to spread drops onto a surface,increasing the spreading abilities of a liquid.Surfactants are usually organic compounds that are amphiphilic,meaning they contain both hydrophobic groups(their tails)and hydrophilic groups(their heads).Therefore,a surfactant contains both a water-insoluble(or oil-soluble)component and a water-soluble component.Surfactants will diffuse in water and adsorb at interfaces between air and water or at the interface between oil and water,in the case where water is mixed with oil.The water-insoluble hydrophobic group may extend out of the bulk water phase,into the air or into the oil phase,while the water-soluble head group remains in the water phase.In the bulk aqueous phase,surfactants form aggregates,such as micelles,where the hydrophobic tails form the core of the aggregate and the hydrophilic heads are in contact with the surrounding liquid.Othertypes of aggregates can also be formed,such as spherical or cylindrical micelles or lipid bi-layers.The shape of the aggregates depends on the chemical structure of the surfactants,namely the balance in size between the hydrophilic head and hydrophobic tail.A measure of this is the HLB,Hydrophilic-lypophilic balance.Surfactants reduce the surface tension of water by adsorbing at the liquid-air interface.The relation that links the surface tension and the surface excess is known as the Gibbs isotherm.
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