It's a product that we use all the time, but shampoo is actually more complex than you might think. As well as cleaning your hair, it can be designed to condition it, reduce dandruff, and make it smell nice. All these added ingredients impact how the shampoo interacts with your hair and can influence how well it works.
Understanding these interactions is crucial for the haircare industry, so they know how best to improve their products. There is also a drive within the industry to move to more sustainable ingredients, and these will also need to be tested before going to production.
Tests using model hair fibres are common, but usually carried out using lab-based techniques or computer simulations. In this study, published in Physical Chemistry Chemical Physics, the team studied the interaction between shampoo ingredients with a model made to mimic damaged hair by using neutron scattering.
The study formed part of lead author Serena Cozzolino's PhD project, which was a collaboration between colleagues from the Institut Laue-Langevin (ILL), the cosmetics company L'Oréal and KTH Royal Institute of Technology in Sweden.
Their focus was the interaction between the hair model and a surfactant, sodium dodecyl sulphate, and the natural polysaccharide, chitosan. Polysaccharides are complex sugars that can be bio-sourced and could replace petroleum-based polymers used in shampoos and other hair care products to reduce frizz, smooth hair, and improve hair quality.
Neutron reflectometry is an ideal investigative tool for this type of study, as the different interaction between neutrons and hydrogen and deuterium means that selective deuteration can be used to build up a contrast picture of the system with sub-nanometre resolution.
The researchers used the Inter beamline at ISIS and the D17 beamline at the ILL alongside quartz-crystal microbalance and atomic force microscopy measurements to build up a comprehensive knowledge of the way these shampoo ingredients adsorb onto hair.
Studying the hair model both with a model shampoo applied, and after “washing", they found that the order in which the different ingredients were added to the hair was important for the way they interacted. Sequential application of soap and chitosan gave different results to when they were applied as a mixture. The aggregation of the chitosan molecules also effected how it interacted with the hair model. This is an important insight to consider when introducing natural ingredients into shampoo products.
In the future, they hope to move to a more complex hair model and introduce other ingredients to see how this impacts the interaction.
Further information
The full paper can be found at DOI: 10.1039/D4CP03603D
