Surface properties of shampoo affected by the way surfactant systems are handled
The research team from the Institut Laue-Langevin centre for neutron science demonstrated quantitatively the science behind an anomaly in the surface tension of surfactant mixtures and outlined a way to reload interfaces with functional components simply by tuning the way the materials are handled.
“By approaching the problem in a different way, we have shown that the way you handle polyelectrolyte/surfactant systems can produce a variety of tuneable surface properties,” says Dr Richard Campbell, of the Grenoble-based research centre.
Future implications for industry
“We hope that our findings will allow future industrial chemists across the pharmaceutical, detergency and cosmetic industries to generate better product output from their raw materials by learning to handle them in a smarter way, and create optimum surface properties on demand, rather than simply buying in more material to improve performance.”
Surface tension is a property of liquids resulting from the cohesion of their molecules that helps them resist an external force and is responsible for the shape of liquid droplets.
Surfactants lower the surface tension of a liquid and can capture other substances, such as oil or grease in cleaning products and are often combined with polyelectrolytes, made of long charged molecules, to improve the efficiency of shampoos and conditioners, amongst other applications.
Appearance of formulation altered and performance reduced
However, whilst adding a surfactant to a polyelectrolyte solution initially causes the surface tension to decrease, as further surfactant is added the surface tension dramatically increases again, affecting the appearance and performance of the mixture.
To investigate this problem, Dr Campbell, Dr Imre Varga from Eötvös-Loránd University in Hungary, and their co-workers looked used neutron reflectometry, a reflection technique used for measuring the composition and structure of thin films, to monitor the surface properties of the mixture.
According to the report, the researchers showed quantitatively for the first time that this striking feature in the surface tension results from the slow precipitation of particles into sediment from the aqueous solution. They explain that the precipitation depletes the solution and consequently the surface of its active ingredients, and also accounts for the loss of cloudiness observed.
As well as uncovering the reasons behind the rise in surface tension, the team were also investigated methods to prevent its impact, which could directly benefit commercial applications. The research suggests that the way these mixtures are handled could affect the nature of the material in the solution - a phenomenon called ‘non-equilibrium effects’.