Engineers at Harvard in conjunction with Unilever researchers have found a way to create gas-liquid systems with bubbles that remain stable for up to a year.
This may help to significantly extend the life of aerated personal care products as well as having implications for the shelf life of foam-based food products, according to Howard Stone from Harvard.
Small bubbles degrade instantly
Small micrometer sized bubbles rarely last longer than a few seconds and gas-liquid systems usually degrade with larger bubbles growing at the expense of smaller ones, explained the researchers.
Current methods to increase the stability of the gas-liquid system include the addition of amphiphilic molecules (molecules that have both water-loving and water-hating properties) but this has previously only increased the lifetime of individual bubbles by a few months.
However, the research published in Science May 30, suggests a way to extend the lifetime of bubbles to a year.
In addition to increased stability, the increased presence of small bubbles (measuring approximately a micrometer) means that the gas-liquid system may have sensory and optical properties of interest to personal care formulators, explained Stone.
"The small bubble size gives the foam a rich white color and a different kind of texture," he said.
Surfactant properties for greater stability
The team were able to produce the stable bubbles by using a glucose-sucrose surfactant which forms a coating around the air bubbles.
In addition, they noted that each bubble had tiny hexagonal patterns on its surface which, they explained, is caused by the amphiphilic nature of the surfactant used.
The hydrophilic (water-loving) heads of the sucrose molecules in the surfactant sit on the outside of the bubble in contact with the water, whereas the hydrophobic (water-hating) chains of the molecule lie on the inside of the bubble. As the heads occupy more surface area than the tails this causes the surface of the bubble to bulge, resulting in the hexagonal patterns that can be observed.
Looking to the future Stone said the researchers were looking to other industries in an attempt to investigate the potential the stable bubbles may have in the creation of other multifunctional ingredients.
