Plasma Treatments to Assist Fluid Manipulation in Microgravity

Lyndon B. Johnson Space Center, Houston, Texas

A recent innovation has made manipulation of hazardous laboratory reagents in microgravity easier, thus enabling even more scientific research to be performed on the International Space Station (ISS). Prior to this innovation, moving fluids from container to container was performed only under conditions of redundant and physically separate layers of containment. This design paradigm restricts access to — and direct manipulation of — fluids in microgravity conditions.

In terrestrial laboratories, transfer of fluid samples from one container to another is easily performed with standard laboratory pipettes or by similar means. This is because gravity can direct the flow of fluids as well as constrain the fluid to the bottom of the container. In microgravity environments, the control of fluid movement and fluid retention is, for obvious reasons, significantly more difficult. By treating the container interior using a process known to impart hydrophilic properties, a location is created on the surface to where fluid will migrate and become anchored.

By exposing the internal surfaces of containers with a localized low-pressure (vacuum) plasma treatment, it is possible to significantly increase (make more hydrophilic) or decrease (make more hydrophobic) the surface energy of the material. Experiments were carried out using a variety of process gases, plasma exposure times, and other process variables that dramatically increased the surface energy within the bottom section of the fluid containment vessels. By leaving the top sections of the containers untreated by the plasma field, fluids were held within the container by the naturally low surface energy of the polymer material.

The advantage of this innovation is that surface tension can be utilized to act as a layer of containment. Microgravity laboratory experiment containers can be engineered so that even fluids exhibiting low surface energy can be anchored to a desired location in the container, aiding the safety of directly manipulating hazardous laboratory reagents under microgravity laboratory conditions by personnel and/or automated equipment.

Additional levels of containment may still be required depending on the toxic hazard level of the fluid, but by using selective plasma treatments, the number of redundant, physical layers of containment can be reduced. Low-hazard-level fluids can essentially be injected into an open-mouth container in microgravity and manipulated in a manner that mimics terrestrial lab fluid transfer by pipette.

This work was performed by Jon A. Genova of Genova Engineering, LLC, and Kevin V. Smith of TriStar Plastics Corp. for Johnson Space Center. For further information, contact the JSC Technology Transfer Office at (281) 483-3809. MSC-25433-1