Collective osmotic shock

Soft materials permeable to solvents — such as cells or vesicles — can rupture as a result of stress build-up stemming from an imbalance in osmotic pressure. Such an osmotic burst has now been multiplied in a coordinated fashion within ordered materials, reports a study in Nature Materials this week. The approach leads to orderly nanoperforated materials that may find applications in photonics, optoelectronics and nanofiltration. To prepare a material for such ‘collective osmotic shock’, Easan Sivaniah and colleagues used self-assembled block-copolymer films consisting of close-packed layers of polymethyl methacrylate (PMMA) globules within a polystyrene matrix. They then broke the globular PMMA down into oligomers using ultraviolet light, and immersed the films in acetic acid — a solvent suitable for the oligomers. As the solvent permeated through the film layer by layer, it swelled the oligomer globules, causing them to deform and rupture in concert. The researchers claim that such a collective osmotic rupture produces periodic nanoporosity within any ordered material containing a minority component that can be selectively degraded and solvated within a deformable matrix. The team demonstrated that these perforated structures behave as one-dimensional photonic crystals, and that they can be used as ultrafiltration membranes and as electrodes in light emitting devices.