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Know about Emulsions

An emulsion is a fine mixture of two naturally immiscible liquids, most commonly water and oil. Emulsions are made possible by a special type of chemical that is called a surfactant or emulsifier, that is friendly to both liquids and which allows these two to coexist.

Emulsions are important in our lives, from protecting our lungs to making our skin feel great, to even harvesting pure oil from crude oil so we can use it as fuel. Emulsions allow for a variety of liquids, which can be used in numerous ways that benefit humanity. Let’s dive in to learn more about how emulsions form and what they can do!

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Full Chemistry of Emulsions

Chemistry of Emulsions

Full Chemistry of Emulsions

An emulsion is a fine mixture of two naturally immiscible liquids, most commonly water and oil. Emulsions are made possible by a special type of chemical that is called a surfactant or emulsifier, that is friendly to both liquids and which allows these two to coexist. The hydrophilic, or “water-loving” component of the emulsifier usually have a charge associated with them, and therefore interacts with water molecules which also has a charge. Conversely, the hydrophobic, or “water-fearing” component, usually lipids, does not have a net charge and is therefore nonpolar, and hence is unable to interact with water.

Because of this dual characteristic, emulsifiers are able to bridge the gap between oil and water by being able to interact with both.

Full Chemistry of Emulsions
Full Emulsifiers and Surfactants

Emulsifiers and Surfactants

Full Emulsifiers and Surfactants

Stabilizing Emulsions with Surfactants

Let’s go back to making a vinaigrette. We might shake vigorously to mix oil and water together, but for the reasons mentioned above, the mixture will quickly separate into two distinct phases.

However, there are many contexts that require the stabilization of oil and water mixtures. How can we lower the energy barrier to prevent separation? The answer lies in the addition of emulsifying agents, also known as surfactants.

Surfactants are molecules or molecular compounds that lower the surface tension at an interface (interfacial tension). In the case of water-oil interface, adding a surfactant will lower the energy barrier for breaking hydrogen bonds among water molecules, and allow more freedom for water molecules to interact with other types of molecules in a given system. Additionally, surfactants have the ability to form micelles, which are a type of molecular “cage” that forms around solute molecules that are normally immiscible in a particular solvent (ie nonpolar molecules can be protected inside a micelle when immersed in a polar solvent).

 

From a chemical perspective, surfactants solve the incompatibility between water and oil because they contain both polar and nonpolar properties, serving as a bridge between polar/aqueous and nonpolar/organic substances. A common surfactant is a phospholipid,such as lecithin, which contains a polar headgroup that interacts with water, and a nonpolar tail that interacts with oils. In an emulsion, a phospholipid would surround the dispersed droplets, creating a micelle, forming a barrier between the water and oil.

This presence of a phospholipid stabilizes the emulsion, preventing the oil and water components from separating. This is incredibly useful in industry, or even in your kitchen!

Full Emulsifiers and Surfactants
Full Classification of Emulsions

Classification of Emulsions

Full Classification of Emulsions

An emulsion is a type of colloidal mixture where normally immiscible liquids are combined in a way that maintains their unique chemical identities. In general, there are two parts of an emulsion:

Continuous Phase: the liquid portion of an emulsion in which another liquid is dispersed

Dispersed Phase: the liquid portion that forms tiny droplets that are evenly suspended throughout the continuous phase

The composition of the continuous and dispersed phases offer one way to classify emulsions.

Full Classification of Emulsions

Created by

Jeanne Garbarino Jeanne Garbarino avatar

Jeanne was once rescued by the FDNY after getting her head stuck in a fence. She then grew up to become a biochemist.
Director of RockEDU Science Outreach
The Rockefeller University
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