First, a definition (from Wikipedia): Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. (In other words, a surfactant makes it possible to mix oil and water or for lathery things to remove oil or dirt from your skin or clothes.)
Surfactants have a hydrophilic (or water-loving) head and a lipophilic (or fat-loving) tail. The hydrophilic head clings onto watery stuff - say the water phase of our lotion - and the lipophilic tail creates a ball around the oily stuff - the oil phase of our lotion (More about this tomorrow with micelles!)
Surfactants come in four flavours (as it were...)
- Anionic - negatively charged
- Cationic - positively charged
- Non-ionic - neturally charged
- Amphoteric - both positive and neutral
These charges are important; they define what kind of emulsifier we need for a specific product. Surfactants can be things like emulsifiers (which are generally non-ionic), conditioning agents (like BTMS or cetrimonium bromide, which are cationic), foamy and lathery things (which are generally anionic, sometimes non-ionic, possibly amphoteric).
In this series of posts, my focus will be the lathery, foamy types of surfactants or surfactants that exhibit detergency - meaning something that wets and solubilizes oils, soils, and proteins, and removes them from surfaces, clothes, and people. They tend to be bubbly, foamy, and lathery.
So if you see the word surfactant in my posts, assume it refers to the bubbly stuff. If I want to talk about emulsifiers or solubilizers or conditioners, I'll call them by those names.
So how do surfactants really work? Join me tomorrow for fun with micelles!