Industrial and applied chemistry

Surfactants, emulsification

How amphiphilic molecules lower interfacial tension, assemble at interfaces and stabilize useful dispersions.

IntuitionWhy oil and water can stay mixed

A surfactant has a water-compatible region and an oil-compatible region. At an oil–water boundary, it can place each region in its preferred environment, making it easier to create droplets and harder for them to merge.

SchoolAmphiphilicity and molecular shape

The balance between head-group area and tail volume influences preferred curvature. Molecular shape is a useful guide, not a complete predictor: hydration, salt, temperature and mixtures also matter.

UndergraduateAdsorption lowers interfacial tension

Creating interface costs free energy. Surfactant adsorption replaces some unfavorable contacts and reduces the energy cost per area. During mixing, this makes creation of small droplets more accessible, although mechanical energy is still needed.

Here $\gamma$ is interfacial tension and $\Delta A$ the area created. Lowering $\gamma$ reduces the free-energy penalty, but does not by itself guarantee long-term stability.

UndergraduateMicelles and the critical micelle concentration

Above a concentration range called the critical micelle concentration (CMC), added surfactant increasingly enters aggregates such as micelles rather than raising the monomer concentration in proportion. The CMC depends on molecular structure, temperature, electrolyte and other solutes.

AdvancedChoosing an emulsifier for a product

An oil-in-water emulsion disperses oil droplets in a continuous aqueous phase; a water-in-oil emulsion does the reverse. The required type depends on use, sensory properties, active ingredients and processing. Hydrophilic–lipophilic balance (HLB) is one empirical selection tool, not a universal law.

AdvancedStability is more than small droplets

Creaming moves droplets under gravity; flocculation groups droplets without merging them; coalescence merges them; Ostwald ripening transfers material from smaller to larger droplets. Interfacial films, viscosity and droplet-size distribution influence these distinct failure routes.

ResearchResearch frontier