Magnetic nanoparticles encased in oily liquid shells spontaneously form chains on exposure to a magnetic field (left). The chains can be broken (middle) and then re-assembled (right).In a paper published in Nature Materials, researchers from North Carolina State University and the University of North Carolina-Chapel Hill show that magnetic nanoparticles encased in oily liquid shells can bind together in water. This behaviour is similar to the way sand particles mixed with the right amount of water can clump together enough to build sandcastles.
"Because oil and water don't mix, the oil wets the particles and creates capillary bridges between them so that the particles stick together on contact," explains Orlin Velev, professor of chemical and biomolecular engineering at NC State and the corresponding author of the paper.
"We then add a magnetic field to arrange the nanoparticle chains and provide directionality," said Bhuvnesh Bharti, research assistant professor of chemical and biomolecular engineering at NC State and first author of the paper.
Chilling the oil is like drying the sandcastle. Reducing the temperature from 45°C to 15°C freezes the oil and makes the bridges fragile, causing the nanoparticle chains to break and fragment. Yet the broken nanoparticle chains will quickly re-form if the temperature is raised again to liquefy the oil and an external magnetic field is applied to the particles.
"In other words, this material is temperature responsive, and these soft and flexible structures can be pulled apart and rearranged," Velev said. "And there are no other chemicals necessary."
This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.