The post, Should we design our recipes as lines of products", put forth the idea that maybe we should be consider what we use together when we are making our products. Can we leave ingredients out or reduce the concentration of ingredients when we know what might be coming next" To that end, let's take a look at the first product most of us use when we're washing our hair - shampoo!
How does shampoo remove sebum, dir, skin cells, and so on from our hair"
The main ingredients in a shampoo are the foamy, bubbly, and lathery ingredients we call surfactants. 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.) (From Wikipedia.)
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.
When it comes to making a shampoo, our 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.
Yes, the emulsifiers we use like Polawax or BTMS are surfactants!
We know that surfactants lower surface tension, but they're also effective at deflocculating soil and dirt clumps in our hair. (Deflocculating means "to disperse an agglomerate into fine particles and form a colloid" - in other words, to disperse a clump of something into finer particles. You might remember flocculation from the epic lotion fail post - this means for finer particl...