Experimental Investigation of Pendant and Sessile Drops in Microgravity

Abstract

The experiments regarding the contact angle behavior of pendant and sessile evaporating drops were carried out in microgravity environment. All the experiments were performed in the Drop Tower of Beijing, which could supply about 3.6 s of microgravity (free-fall) time. In the experiments, firstly, drops were injected to create before microgravity. The wettability at different surfaces, contact angles dependance on the surface temperature, contact angle variety in sessile and pendant drops were measured. Different influence of the surface temperature on the contact angle of the drops were found for different substrates. To verify the feasibility of drops creation in microgravity and obtain effective techniques for the forthcoming satellite experiments, we tried to inject liquid to create bigger drop as soon as the drop entering microgravity condition. The contact angle behaviors during injection in microgravity were also obtained.

The influence of gravity on the distribution of the deposit formed onto a substrate by sessile, hanging, and sandwiched hanging drop evaporation

“…For pure liquid drops, it has been suggested [20] that hanging drops stick to a surface more strongly than corresponding sessile drops. Other reports [21] present the influence of gravity on the shape of a sessile or a hanging drop. For colloidal suspensions, to the best of the authors knowledge, there are only two references suggesting that gravity could influence considerably the structure of the ring patterns [22], the width of the ring, and the amount of material deposited in the area enclosed by the ring [23].…”

Thermodynamic Behaviors of Macroscopic Liquid Droplets Evaporation from Heated Substrates

“…6. Compared with the experimental data at the low gravity level by Zhu et al (2010), drop's shape on ground seemed flattened at early stage so that spherical cap shape could not correspond to the macroscopic-scale droplet. But after a few moments when the diameter reduced to the capillary length or even less than it, the contour fitted the assumption of spherical cap well.…”

The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity

“…Recently, Bormashenko imposing the transversality conditions on the variational problem of wetting also demonstrates that gravity does not influence equilibrium contact angles [35][36][37]. However, many experimental observations [15][16][17][18][19][20][21][22][23][24][25][26][27] under some gravities (≤2G) differed from these theoretical conclusions. This discrepancy becomes an important issue, especially in the space era, when interfacial phenomena frequently draw more attention because they are dominant events in microgravity and much different from those observed on Earth.…”