Binary Colloidal Alloy Test (BCAT-5)

Everyday we use or consume colloids for many different purposes. Did you know that if you drink a glass of milk, you consume colloids? If you paint the walls of your home, you use colloids to create a protective coating for the wall.

The BCAT-5 Team. From left to right: Marcus Dejmek, Dr. Arthur Bailey, Dr. Barbara Frisken, Canadian astronaut Bob Thirsk and Bastien Dufour. (Credit: CSA)

Colloids are microscopic particles suspended in another material such as a liquid. For example, milk is a colloidal suspension consisting of protein-lipid globules suspended in liquid water. The fat globules are the colloids. Unlike a solution, such as soap in water, these particles do not dissolve.

Scientists study colloids for two reasons. First, obtaining a better understanding of the properties of these fascinating suspensions leads to the discovery of new materials and new methods of processing materials. For example, the polishing processes used in industry result from scientific research on polishing slurries, which are colloidal suspensions. Secondly, in addition to the practical reasons, colloidal suspensions serve as excellent models of atoms and molecules, with the advantage that they can be seen more easily and that the forces between the colloidal particles can be easily tuned. Thus, colloidal research provides insight into the properties of many other materials.

On Earth, many exciting colloidal materials cannot be explored because the colloids sediment due to gravity. To research such systems, scientists are exploiting the microgravity environment of the International Space Station (ISS).

The BCAT-5 apparatus with three colloidal samples provided by the Canadian team. (Credit: NASA)

About the size of a laptop computer, BCAT-5 contained ten different colloidal samples. Canadian scientists Dr. Barbara Frisken and Dr. Arthur Bailey of Simon Fraser University (SFU) have prepared three of the ten samples. Using BCAT-5, the scientists hope to perform the first measurements of processes that occur when gas, liquid and crystal phases all form simultaneously from a single homogeneous sample. Each sample has a different concentration of the same colloids suspended in a liquid. Polymers are added to precisely tune the forces between the particles creating the remarkable three-phase samples.

Assembled with camera, BCAT-5 being tested in laboratory. (Credit: NASA)

During Expedition 20/21, which began on May 27, 2009, Canadian astronaut Dr. Robert (Bob) Thirsk performed colloid experiments aboard the ISS. He first set up the BCAT-5 apparatus, stirred the colloid samples with a magnet to homogenize them, and then installed a camera to record images of the samples as they evolve slowly over time. This visual information was transmitted to scientists on the ground for data analysis. The images will be analyzed by the SFU science team to determine the process of phase separation and crystal growth.

Understanding colloids' behavior will lead to innovative manufacturing processes and improved commercial products. BCAT-5 is an example of Canadian microgravity science excellence.