Moore Foundation grantee Paul Chaikin and colleagues at New York University report the self-assembly of magnetic nanoparticles into clusters capable of moving faster than the individual particles themselves.
Particles or other objects form stable clusters under mostly well-understood conditions driven by thermodynamic and kinetic forces, like when sand (made of microscopic particles) collects at the bottom of a glass filled with water.
However, when a perturbation or other disturbance is created at the boundary between different systems — such as the application of a magnetic field — instabilities can arise. In this case, Chaikin and his team leveraged such an instability to study an ensemble of magnetic microscopic rollers driven through a viscous fluid by a rotating magnetic field.
In this system, clusters originate from a previously unreported instability, in which fingers pinch off from an unstable front to form critters whose size depends on the height of the particles above the floor. These critters are a stable state of the system, move much faster than individual particles and quickly respond to a changing field.
The authors state "this instability is generic and should be found in any system of particles rotating parallel to a floor, provided that hydrodynamics is the dominant particle-particle interaction."
This unique formation of clusters — what the authors call "critters" — could be used in microfluidic "lab-on-a-chip" devices designed to transport and deliver chemical or biological species.
Read the full article here.
Message sent
Thank you for sharing.