The Microgravity Research Experiments (MICREX) Database

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"A foam consists of bubbles of gas encased by walls of thin liquid films. Although some foams can be made rigid or flexible and durable, the characteristic foam is not stable on Earth. Foams collapse primarily as a result of the gravity-induced drainage of liquid in the bubble walls. As the liquid drains from the bubble, the film walls become increasingly thin until, at a thickness of approximately 10 nanometers (100 angstroms), they are ruptured by random molecular motion. Thus, the foam gradually dissipates as more of the liquid drains away to bulk form and leaves less to support the bubble walls. In the zero-g environment of space, drainage is substantially reduced; therefore, a longer lasting foam is provided. Drainage, however, is only one of the mechanisms contributing to the dissipation of foams. Evaporation and liquid spreading also act to dissipate bubble walls. Thus, the full extent of foam stability is still uncertain.

"Forming a foam in space yields a very large surface area-to-volume ratio of the liquid that should be retained for a relatively long period. This large, stable surface area should enable surface-sensitive chemical reactions to occur differently than they would on Earth. The sensitivity of some chemical reactions to the size of the interface area has long been known....However, the precise change taking place at the interface has not been precisely determined, and definitive theories on the characteristics of a stable foam in space have not been generated. Nevertheless, it was anticipated that a chemical reaction dependent on the surface area of the air-to-liquid interface... would proceed differently in a foam in a zero-g environment than would normally occur on Earth." (3, pp. 31-2 - 31-3)

This experiment was one of two chemical foam science demonstrations designed by Grodzka et al. performed during the ASTP mission. (See Grodzka, ASTP, "The Formaldehyde Clock Reaction/Chemical Foaming" to review the other experiment.) The specific objective of the Equilibrium Shift Reaction Experiment was to visually demonstrate the stability of foams under low-gravity conditions.

Prior to the initiation of the experiment, it appears that two Lexan test tubes were each filled with a gold-colored solution comprised of (1) 10.7 mg thymol blue, (2) 10 ml ethyl alcohol, (3) 0.2 cc concentrated hydrochloric acid, and (4) 500 ml distilled water. (Thymol blue of pH 2.8 will turn from brown amber to pink when foamed by shaking.)

During the ASTP experiment, a crew member shook the tubes and the resulting pink foams were recorded on motion picture film. The contrast of the brightly colored pink foam against the gold bulk solution was clearly visible to the crewman as the foam dissipated.

It was reported that (a) the foams created under low-gravity conditions were very stable while those foams created on Earth collapsed within a few seconds, and (b) because the "...16 millimeter motion picture was out of focus, detailed knowledge of the foam dissipation [time] in the pink foam has not been determined." (3, p. 31-4)

No other results from this experiment were reported.

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(2) Grodzka, P. and Facemire, B.: Chemical Reactions in Low-G. American Institute of Aeronautics and Astronautics 16th Aerospace Sciences Meeting, Huntsville, Alabama, January 16-18, 1978, 5 pp. (post-flight)

(3) Snyder, R. S., Clifton, K. S., Facemire, B., Whitaker, A. F., Grodzka, P. G., and Bourgeois, S.: Science Demonstrations. In Apollo-Soyuz Test Project--Preliminary Science Report, NASA TM X-58173, February 1976, pp. 31-1 - 31-9. (post-flight)

(4) Grodzka, P. G. and Bourgeois, S. V.: The Apollo Soyuz Science Demonstration Experiments; Final Report. Lockheed Missiles and Space Company, Inc., LMSC-HREC-TR-D497499, October 1977, work performed under NASA/MSFC Contract NAS8-32222.

(5) Naumann, R. J. and Mason, E. D.: Chemical Foams. In Summaries of Early Materials Processing in Space Experiments, NASA TM-78240, August 1979, p. 72. (post-flight)

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