Box 23-2 What Is a Micelle

A micelle is an aggregate of molecules with ionic head-groups and long, nonpolar tails. Such molecules are called surfactants, an example of which is sodium dodecyl sulfate  

Nonpolar organic molecule dissolved in interior of micelle 

The polar headgroups of a micelle face outward, where they are surrounded by polar water molecules. The nonpolar tails face inward, where they form a little pocket resembling a nonpolar hydrocarbon solution. Nonpolar solutes are soluble inside the micelle. 

At low concentrations, surfactant molecules do not form micelles. When the concentration exceeds the critical micelle concentration, spontaneous aggregation into micelles occurs. Isolated surfactant molecules exist in equilibrium with micelles. 

Neutral molecule equilibrates between free solution and inside of micelle 

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