Hey Poonam,

As you said emulsifiers are material that has both hydrophobic and hydrophobic groups. Suppose you have to make oil-in-water emulsion which you want to stabilize. In this case you need to choose a emulsifier which has hydrophobic and hydrophilic part. The hydrophobic part will attach to the oil droplets and the hydrophobic part will be in the water medium. When one emulsion droplet will come near to another one and try to combine to minimize the surface energy, there emulsifiers will repel each other by steric force or by electrostatic repulsion. Due to this the oil droplets will stay separated from each other the emulsion will be stabilized.

hope it helps...I will send you a good reference soon

Thank you @Sudhanshu Pati. Looking forward for the reference.

When a surfactant adsorbs on the interface the interfacial tension between the two phases decreases. The reduced interfacial tension depends on the concentration of the surfactant according to the Gibbs’ isotherm.

Adsorbed surfactants or solid particles stabilize emulsions via two main mechanisms:

1. steric stabilization

2. electrostatic stabilization

Steric stabilization arises from a physical barrier to contact and coalescence. For example, high-molecular-weight polymers can adsorb on the surface of the dispersed phase droplets and extend significantly into the continuous phase, providing a volume restriction or a physical barrier for particle interactions. As polymer coated particles approach, the polymers are forced into close proximity and repulsive forces arise, keeping particles apart from each other. Surface-active solid particles such as clays have also been shown to sterically stabilize emulsions.

Electrostatic stabilization is based on the mutual repulsive forces that are generated when electrical charged surfaces approach each other. In an electrostatically stabilized emulsion, an ionic or ionisable surfactant forms a charged layer at the interface. For an oil-in-water emulsion, this layer is neutralized by counter ions in the continuous phase. The charged surface and the counter ions are termed a double layer. If the counter ions are diffuse (thick double layer), the disperse phase droplets act as charged spheres as they

approach each other. If the repulsive forces are strong enough, the droplets are repelled before they can make contact and coalesce, and the emulsion is stable.

In general, electrostatic stabilization is significant only for oil-in-water emulsions since the electric double-layer thickness is much greater in water than in oil.

Both electrostatic and steric forces can prevent aggregation or coalescence and

hence stabilize emulsions.

Reference: Urrutia P.I., Predicting Water-In-Oil Emulsion Coalescence From Surface Pressure Isotherms, Department of Chemical and Petroleum Engineering, University of Calgary M. Sc. Thesis, 2006.

I hope it was useful for you.

http://lcpe.uni-sofia.bg/files/publications/2008/2008-03-SC-ND-AL-PCCP-Particles-Emulsifiers.pdf

Dear Poonam,

you should consider that emulsifier action is more than stabilization.

Importantly there is the process of emulsion formation. Reduction of interfacial tension is important in this step but also adsorption kinetics. In the process of emulsion preparation mostly droplet formation and coalescence occurs simultaneously. Depending on the time scale of droplet formation, adsorption has to be fast enough to ensure stabilization before droplet coalescence. Therefore efficiency of emulsifiers during emulsification depends on a good fit of adsorption kinetics to the process of droplet generation, efficient lowering of surface tension and stabilization.

Principles of stabilization against coalescence were already well described in the previous comments. Similar considerations may apply for stabilization against flocculation, though weak flocculation may stabilize against creaming or sedimentation.

Stabilization against phase inversion may be achieved by including a very polar surfactant like an ionic surfactant to prevent phase inversion from o/w to w/o. Stabilization against Ostwald ripening has to be ensured by other additives than emulsifiers.

Thank you Sir, for the explanations.

I just repeat the answer I posted on another quastian of yours, POONAM. Surfactant stabilizes colloid systems, including emultions, due to LARGE OSMOTIC REPULSION FORCE at the conditions of ADSORBED SURFACTANTS MONOLAYERS OVERLAP.

Dr. SCHRAMM and I recently published paper in COLLOIDS and SURFACES B. The full text of this paper is posted as #1 on my RG site. And no comlicated Math is involved.

Some times I can see claims that electric charges play significant role in the stability of WATER - IN - OIL emultions. In reality, surface charges, falling on the oil phase are very small, most of the charge is compensated in EDL within water droplets. These emulsions can be very stable in Crude Oils due to the presence of Natural Surfactants, adsobed at O/W Interface.

One can try to prepare W-in-O Emulsion in Synthetic Paraphinic Oil, even in DECANE, using sonifier to disperse water. As no no natural surfactants are expected in Syntetic Oil mentioned, emulsion will collapse in no time, no help from electric charges will be observed.

All emulsifying agents concentrate at and are adsorbed onto the oil:water interface to provide a protective barrier around the dispersed droplets. In addition to this protective barrier, emulsifiers stabilize the emulsion by reducing the interfacial tension of the system. Some agents enhance stability by imparting a charge on the droplet surface thus reducing the physical contact between the droplets and decreasing the potential for coalescence. Some commonly used emulsifying agents include sodium dioctyl sulfosuccinate, tragacanth, sodium lauryl sulfate, and polymers like Tweens. Emulsifying agents can be classified according to: 1) chemical structure; or 2) mechanism of action. I'm not going into detail in this regard. Regardless of their classification, all emulsifying agents must be chemically stable in the system, inert and chemically non-reactive with other emulsion components, and nontoxic and nonirritant. They should also be reasonably odorless and not cost prohibitive.

'Finely divided solids are known for forming a particulate film at o/w interface and by formation of solid film, pose a barrier to coalescence, However, this class is of least interest as it is seldom used.' ???

Interest is not only defined by percentage of application cases.

Of importance here is effectiveness, economics, potential etc.

As we know , there are many kinds of emulsifiers, anionic , non anionic and etc, How to find out (recognize) which emulsifier is more suitable for stabilizing of oil-water (Oil in water) ?

Dear poonam

You can find good ideas here.