We describe a setup to perform systematic studies on the spreading of droplets of complex fluids under microgravity conditions. Tweaking the gravitational acceleration under which droplets are deposited provides access to different regimes of the spreading dynamics, as quantified through the Bond number. In particular, microgravity allows us to form large droplets while remaining in the regime where surface tension effects and internal driving stresses are predominant over hydrostatic forces. The vip-drop2 (visco-plastic droplets on the drop tower) experimental module provides a versatile platform to study a wide range of complex fluids through the deposition of axisymmetric droplets. The module offers the possibility to deposit droplets on a precursor layer, which can be composed of the same or a different fluid. Furthermore, it allows us to deposit four droplets simultaneously while conducting shadowgraphy on all of them and observing either the flow field (through particle image velocimetry) or the stress distribution inside the droplet in the case of stress birefringent fluids. It was developed for a drop tower catapult system, is designed to withstand a vertical acceleration of up to 30 times the Earth’s gravitational acceleration in the downward direction, and is capable of operating remotely under microgravity conditions. We provide a detailed description of the module and an exemplary data analysis for droplets spreading on-ground and in microgravity.

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Axisymmetric droplets provide a demonstration system to study the spread of complex fluids, which are an essential component of industrial and technological processes, among which additive manufacturing (AM). Tweaking the gravitational environment provides access to different regimes, quantified through the Bond number; in particular, microgravity allows to form large droplets while remaining in the regime where the surface tension effects and internal driving stresses are predominant over hydrostatic forces. The vip-drop 2 module offers a versatile platform to study a wide range of complex fluids through the deposition of initially axisymmetric droplets. It offers the possibility to deposit the droplets on a precursor layer: a thin, homogeneous layer, which can be made of the same or of a different fluid. Besides, it allows to deposit simultaneously 4 droplets, while conducting shadowgraphy on all of them, and observing either the flow field through particle image velocimetry (PIV), or the stress distribution within the droplet in the case of stress birefringent materials. Developed for a drop tower catapult system, it is designed to withstand a vertical acceleration of up to 30 times the gravity of Earth in the downwards direction, and can operate remotely, under microgravity conditions.