Measurement of critical contact angle in a microgravity space experiment

Mathematical theory predicts that small changes in container shape or in co ntact angle can give rise to large shifts of liquid in a microgravity envir onment. This phenomenon was investigated in the Interface Configuration Exp eriment on board the NASA USML-2 Space Shuttle flight. The experiment's "do uble proboscis" containers were designed to strike a balance between confli cting requirements of sizable volume of liquid shift (for ease of observati on) and abruptness of the shift (for accurate determination of critical con tact angle). The experimental results support the classical concept of macr oscopic contact angle and demonstrate the role of hysteresis in impeding or ientation toward equilibrium.