ALBUQUERQUE, N.M. It may seem obvious that dunking relatively spherical objects in a sauce blueberries in melted chocolate, say will result in an array of completely encapsulated berries.
Relying on that concept, fabricators of spherical nanoparticles have similarly dunked their wares in protective coatings in the belief such encapsulations would prevent clumping and unwanted chemical interactions with solvents.
Unfortunately, reactions in the nanoworld are not logical extensions of the macroworld, Sandia National Laboratories researchers Matthew Lane and Gary Grest have found.
In a cover article this past summer in Physical Review Letters, the researchers use molecular dynamics simulations to show that simple coatings are incapable of fully covering each spherical nanoparticle in a set.
Instead, because the diameter of a particle may be smaller than the thickness of the coating protecting it, the curvature of the particle surface as it rapidly drops away from its attached coating provokes the formation of a series of louvres rather than a solid protective wall (see illustration).
"We've known for some time now that nanoparticles are special, and that 'small is different,'" Lane said. "What we've shown is that this general rule for nanotechnology applies to how we coat particles, too."
Carlos Gutierrez, manager of Sandia's Surfaces and Interface Sciences Department, said, "It's well-known that aggregation of nanoparticles in suspension is presently an obstacle to their commercial and industrial use. The simulations show that even coatings fully and uniformly applied to spherical nanoparticles are significantly distorted at the water-vapor interface."
Said Grest, "You don't want aggregation because you want the particles to stay distributed throughout the product to achieve uniformity. If you have particles of, say, micron-size, you have to coat or electrically charge them so the particles
|Contact: Neal Singer|
DOE/Sandia National Laboratories