The work was carried out by teams from research groups INRA, CEA and CNRS and in this case, the researchers studied a particular surface-active molecule, the 12-hydroxystearic fatty acid, produced from castor oil, with the results published in the August 29th issue of Angewandte Chemie.
Since it is produced from an organic molecule, the researchers coined the term 'green chemistry' for their work, and it creates new possibilities because foams have many industrial uses. For example, it should be possible to produce shampoos in which the quantity of foam can be controlled simply by adjusting temperature, thus facilitating drainage.
Some cosmetic products require numerous chemical ingredients to produce a stable foam, so use of 12-hydroxystearic acid would limit the quantity of synthetic ingredients while retaining 'foaming' properties over a longer period.
Due to their particular texture and the molecules that compose them, foams often have detergent properties. In physical chemistry, such molecules, which must be dispersed in water to create foam, are called “surface-active”.
This is the first time where such a stable foam has been created with such a simple, natural surface-active molecule. The transition temperature between the state where the foam contains tubes and the 'nano' state depends on the salt chosen to disperse the molecule in water, which increases its potential uses.
In order to disperse the molecule which is initially insoluble in water, the researchers added a salt and then demonstrated the unique advantages of the surfactant, as even in small quantities, it produces abundant foam and, above all, remains stable for more than six months, in contrast with traditional surfactants that stabilize foams for only several hours.
The researchers demonstrated that within a range of average temperatures between 20 and 60°C, 12-hydroxystearic acid, mixed with the 'right' salt, disperses in water in the form of tubes that are several microns in size.
Temperature can affect the state and size
The tubes form a structure that is perfectly stable and rigid in very thin films of water located between air bubbles, which explains the foam’s resistance.
According to the research, when the temperature is above 60°C, the tubes merge into spherical assemblies that are a thousand times smaller (several nanometers), which the researchers call “micelles”.
The previously stable foam then collapses because the rigid structure disappears, and the researchers claim this transition is reversible.
According to the report, if the foam’s temperature is increased, its volume will diminish when micelles start to form, and if the temperature is again reduced to between 20 and 60°C, the tubes will form again and the form will re-stabilize (to regain the initial volume of the foam, air must be re-injected).