The Self-Assembling Particles That Come from InSPACE

Jan. 7, 2013 — Shape-shifting malleable, gelatinous forms are orbiting Earth at this very moment -- assembling and disassembling, growing as they are bombarded by magnetic pulses. These forms will take shape as astronauts run experiments involving smart fluids aboard the International Space Station.

NASA astronaut Suni Williams photographing InSPACE-3 vial assembly after particles redistribution operation on the International Space Station. (Credit: NASA)

While they may change shape, the forms are not things of science fiction. They are the things of fundamental science.

The purpose of the Investigating the Structures of Paramagnetic Aggregates from Colloidal Emulsions-3, or InSPACE-3, study is to gather fundamental data about Magnetorheological, or MR fluids. These fluids are a type of smart fluid that tends to self-assemble into shapes. When they are exposed to a magnetic field, they can quickly transition into a nearly solid-like state. When the magnetic field is removed, they return to a liquid state.

"Initially the particles in the fluid form long, thin chains," said Eric Furst, InSPACE-3 principal investigator, University of Delaware, Newark, Del. "The magnetic dipoles induced in the particles cause these singular chains to grow parallel to the applied field. Over time the chains parallel to each other interact and bond together. These 'bundles' of chains become more like columns when the magnetic field is toggled on and off. And these columns grow in diameter with time exposed to a pulsed magnetic field."

This self-directed "bundling" was never before observed until it was seen in an earlier space station investigation, InSPACE-2, which ended in 2009. The results of InSPACE-2 were highlighted in a September 2012 article titled "Multi-scale Kinetics of a Field-directed Phase Transition" published in the Proceedings of the National Academy of Sciences.

"Earlier InSPACE investigations looked at MR fluids composed of spherical, or round, particles," said Bob Green, InSPACE-3 project scientist, NASA's Glenn Research Center, Cleveland, Ohio. "InSPACE-3 is focused on oval or ellipsoid-shaped particles. The expectation is that these shapes will pack differently and form column-like structures differently than in previous experiments. The particles in InSPACE-3 are made of a polystyrene material embedded with tiny nano-sized iron oxide particles."

Iron oxide is chemically similar to rust. In fact, when the fluid is mixed, it has a brownish rust-type hue. Astronauts, under the direction of the project team, are currently running a series of experiments on this rust-colored mixture and will continue to do so for the next few months.

"We have six vials of which three are primary and three are backups," said Nang Pham, InSPACE-3 project manager at Glenn. "We'll run 12 tests on each of the three vials of different sized ellipsoid-shaped particles for a total of 36 test runs."

A test run could be changing the frequency of the magnetic pulse, altering the magnetic field strength, or using different particle sizes. The first InSPACE-3 test was Oct. 5. Plans are to complete the test runs in early 2013.

For the investigation, astronauts apply a magnetic field of a certain strength, which is pulsed from a low frequency of around 0.66 hertz up to 20 hertz. The pulse is on for a very short time and then is turned off. Scientists are looking for formation of structures that are at a lower energy state. Typically in an MR fluid application, a constant field is applied and the particles form a gel-like structure. They don't pack very well, so the particles have no definite form. They are like a cloud or hot glass that can form into almost any shape.

In a pulsed field, the on-off magnetic field forces the particles to assemble, disassemble, assemble, disassemble and so on. This on-and-off action occurs in millisecond pulses over the approximately two hours of the experiment. In this pulsed field, the particles organize into a more tightly packed structure. Scientists can then measure and plot the column growth over time.

"The idea is to understand the fundamental science around this directed self-assembly in the hopes of better defining new methods of manufacturing materials composed of small colloidal or nanoparticle building blocks," Furst said.

New manufacturing models resulting from InSPACE-2 and -3 studies could be used to improve or develop active mechanical systems such as new brake systems, seat suspensions, stress transducers, robotics, rovers, airplane landing gears and vibration damping systems.

Coupled with the work of InSPACE-2, the InSPACE-3 investigation into fundamental science could advance these systems and improve how we ride, drive and fly. Thanks to these space station investigations, the fluids that come from space may one day further improve your daily commute, whether on the highway or off the road.