52 nanotimes News in Brief

Water Filtration // Self-Healing Dynamic Membrane, © Based on Material by CNRS / ENSCM, France T

Taking their inspiration from cellular membranes, researchers from the Institut Européen des Membranes (CNRS / ENSCM / Université Montpellier 2) in collaboration with the Institut de Chimie Radicalaire (CNRS / Aix-Marseille Université) have developed the first dynamic membrane for water filtration which, depending on the water pressure, can adjust the size of its pores in an autonomous manner. In addition, it is capable of repairing itself if it breaks, thereby prolonging its lifetime and ensuring greater safety of the filtered product.

The dynamic membrane is made of a combination of three polymers with different solubilities that form micelles, nanoparticles in constant interaction with each other. Up to a certain pressure, when the force of water increases, these micelles have a tendency to flatten out and thus reduce the size of the pores within the membrane. 

For instance, at a low pressure of approximately 0.1 bars, the size of the pores is around 5nm, which allows macromolecules and viruses to be filtered. By moderately increasing the pressure, pores of the order of 1nm are obtained, which blocks the passage of salts, colorants and surfactants. However, if the pressure is raised to 5 bars, the morphology of the membrane undergoes a drastic change and the pores reach a diameter of more than 100nm, which instead makes it possible to filter bacteria and suspended particulate matter. This unique property will allow users to employ a single type of membrane for all their filtration requirements.

These 1.3µm-thick dynamic filters are capable of self-healing. If the membrane tears, the physical equilibrium that holds the micelles together is broken. The micelles then seek to restore this equilibrium and reorganize themselves so as to fill the tear. A perforation 85 times larger than the thickness of the membrane can thus be repaired without human intervention and without stopping the filtration operation. 

Prashant Tyagi, André Deratani, Denis Bouyer, Didier Cot, Valérie Gence, Mihail Barboiu, Trang N. T. Phan, Denis Bertin, Didier Gigmes, Damien Quemener: Dynamic Interactive Membranes with Pressure-Driven Tunable Porosity and Self-Healing Ability, In: Angewandte Chemie International Edition Early View, June 13, 2012, DOI:10.1002/anie.201201686:

http://dx.doi.org/10.1002/anie.201201686

Images:

Schematic representation of a membrane failure (red impact) immediately repaired by water flow- ing through it (blue). © Damien Quémener

Scanning electron microscopy image of the membrane with an atomic force microscopy enhancement of the surface. © Institut Européen des Membranes