Liquid membrane blocks small particles and lets big ones through

Tak-Sing Wong Lab

A SELF-HEALING liquid membrane has been developed that acts as a reverse filter by blocking small particles while letting larger ones through.

Particle separation is used in many different fields, from medical diagnostics to wastewater treatment. However, conventional filters are porous to allow smaller particles through while catching larger objects. Researchers at Pennsylvania State University, US, have now developed a membrane that does the opposite.

Inspired by cell walls, which allow large particles through without fluid exchange, they created an all-liquid membrane that separates particles based on their different kinetic energies rather than size. "Typically, a smaller object is associated with lower kinetic energy due to its smaller mass," said Tak-Sing Wong, professor of mechanical and biomedical engineering at Pennsylvania. "So, the larger object with a higher kinetic energy will pass through the membrane, while the smaller object with lower kinetic energy will be retained."

The object is enveloped as it passes through, which allows the membrane to self-heal over the top of the object so that the membrane remains intact.

The membrane is created with deionised water and a surfactant which stabilises the interface between the liquid and air. They can also use a complex multicomponent system design to create membranes for specific purposes. "You could add components that make the membrane last longer or components that allow it to block certain gases," said Birgitt Boschitsch, graduate student in mechanical engineering and lead author of the study. "There are endless potential additives to choose from to tailor a membrane to the application of interest."

The membrane could have lots of potential applications. For example, in regions where clean operating rooms are unavailable, surgeons could use a membrane to keep contaminants out of a wound while still allowing surgical tools to pass through. The membrane could last for over three hours, which equates to over 3,000 film perturbations, without rupturing.

The membrane could also be used as a barrier against small particles like dust or pollen, or stop slow-moving insects such as mosquitos, which could prevent the spread of disease.

Future work will involve developing membranes with enhanced functions and collaborating with other researchers to test its viability for different applications.

Science Advances http://doi.org/ctx7