Surface Free Energy Measurement of Low Energy and High Energy Surfaces in Microgravity Conditions

Abstract

This study presents a comprehensive exploration of a theoretical model designed to measure the surface energy of solids under microgravity conditions. While numerous studies have investigated various techniques for determining the surface energy of solids through the use of pairs of liquids based on Young’s equation of contact angle, these methods often lack accuracy and are impractical in space-like environments due to safety concerns. In this investigation, we critically examine and validate the sessile drop accelerometry model, specifically developed for measuring the surface free energy of solids in microgravity conditions through the deposition of a single water droplet. This model encompasses a set of governing equations that enable the determination of interfacial energies as a function of changes in the droplet’s shape resulting from the release of gravitational energy. To validate and analyze the theoretical model, a sophisticated experimental payload was developed, and a series of rigorous experiments were conducted under both reduced gravity and hypergravity conditions, simulated using parabolic flight. The measured surface free energy values were compared against traditional polar-nonpolar-based surface energy measurement techniques, demonstrating strong agreement and highlighting the robustness of the SDAcc model. Through rigorous theoretical and experimental analyses, this study establishes a fundamental understanding of the influence of gravity on metastable droplet morphology and its implications for accurate surface energy determination. These findings will contribute to the advancement of interfacial science in reduced gravity environments and open new avenues for surface characterization techniques in space applications.