Astronauts collaborate on professors' experiment

by Maria LoBiondo


While the nation focused on astronaut John Glenn's return to space, Chemical Engineering Professor William Russel and Physics Professor Paul Chaikin monitored their own version of a space encore.

An experiment of theirs with colloids--fine particles dispersed in a fluid--was performed in 1995 aboard the space shuttle Columbia. NASA funded that experiment, Dynamics of Colloidal Disorder-Order Transition (CDOT) and the similar experiment CDOT-2 conducted during the Discovery mission STS-95, which was in orbit Oct. 29 to Nov. 7, 1998.

CDOT-2 was part of a series of experiments designed to help scientists answer fundamental science questions and reduce the trial and error involved in developing new and better materials.

Though colloids are currently used in the technology of materials ranging from paints to drugs to foods, many aspects of their behavior are still poorly understood.

Better understanding of the structure of colloids may allow scientists to manipulate their physical properties to develop new materials or improve products already in use.

Nagging mystery

Just what happens when a liquid turns into a solid? It sounds like a simple question, but for Professors Russel and Chaikin, the specifics of how atoms interact in an orderly way, forming rigid patterns to make a solid, or in a disorderly way, flowing in a liquid state, is a nagging mystery. Colloids, perfect spheres all the same size, are larger than atoms and are used to model atomic behavior.

In the recent space experiment, eight test colloid samples in various densities were made with what is commercially called Plexiglass. The spheres were about one-tenth the thickness of a human hair. The astronauts recorded what the samples did when gravity was not a variable in their interaction.

The experiment tested whether the colloids would form a crystal (an ordered solid) or a glass (which has a rigid structure but is not ordered). The entire experiment was performed in a "glovebox," a small container where an astronaut reached in to handle the materials with attached gloves rather than holding the samples directly.

Crystal or glass

As Professors Russel and Chaikin explained it, the most surprising finding of their 1995 experiment was that a sample with a density of 60 percent, which did not crystallize in a year on Earth, did so in space in less than two weeks.

Another sample, with a density a little greater than 50 percent, produced large dendritic crystals in space.

"We thought they'd grow more compactly, like crystals that settle to the bottom of a cyli nder. But in microgravity, they didn't settle. They formed dendrites, looking like snowflakes," Professor Chaikin said.

CDOT-2 chief scientist Zhengdong Cheng *98, right, and Bill Meyer, the National Center for Microgravity Research CDOT-2 Project Scientist, discuss preliminary results of CDOT-2 during the STS-95 mission in the Telescience Support Center for Microgravity Experiments of NASA Lewis Research Center, Cleveland, Ohio.

The new experiments confirmed the 1995 results, according to Zhengdong Cheng, who monitored the experiments from a NASA control center in Cleveland, Ohio. Dr. Cheng received his Princeton doctorate in physics two days before the space mission.

Th e larger picture of what the experiment means to both professors differs.

"For Paul, a condensed matter physicist, the focus is on how solids make the transition," Professor Russel said. "For me, the experiments give an understanding of very concentrated colloidal dispersions, which are ubiquitous in the chemical and materials processing industries."

NASA has approved a project for Professors Russel and Chaikin for two more experiments that may be done on the future space station in 2002.