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Cross-laboratory Comparative Study of Titan’s Haze Analogs: Characterizing Surface Energy of Tholin Samples

Presentation #208.03 in the session Titan I: Atmosphere (Oral Presentation)

Published onOct 23, 2023
Cross-laboratory Comparative Study of Titan’s Haze Analogs: Characterizing Surface Energy of Tholin Samples

The photochemical haze observed in Titan’s nitrogen-methane atmosphere, resulting from the synthesis of complex organic particles, profoundly influences various atmospheric and surface phenomena on this intriguing moon. Tholins, aerosol analogs of Titan’s atmosphere, have been generated in different laboratories, and the surface energies of several samples have been examined and compared [1]. In this study, built on [1], we aim to compare diverse tholin samples by characterizing their surface energies. Understanding the surface energy of Titan’s organic haze can provide insights into the cohesion of aerosols and Titan’s surface materials. In this study, we produced 22 tholin samples using three independent laboratory facilities: the COSmIC chamber at NASA Ames Research Center (NASA/ARC), the PHAZER chamber at John Hopkins University (JHU), and the PAC chamber at University of Northern Iowa (UNI). We produced two samples groups: 1) pristine samples that were transported in dry nitrogen/vacuum; 2) exposed samples that are exposed to ambient air for 45 days. Each set of samples are deposited on at most three types of substrates: glass slides, mica discs, or quartz discs. Surface energies were determined using contact angle measurements using diiodomethane (nonpolar) and water (polar). We have two measuring environments: 1) for the pristine samples, an inert nitrogen atmosphere (<1% relative humidity, RH), and 2) for the exposed samples, ambient air (14-39% RH). The surface energy results reveal that tholin samples deposited on different types of substrates exhibit similar surface energies, suggesting that substrate type has negligible effects. However, pristine plasma samples have very different surface energies compared to the exposed samples. Since pristine samples are considered more analogous to Titan aerosols than exposed samples, this study underscores the importance of performing material characterization under inert atmospheres to obtain the true nature of tholin properties. Among all the unexposed samples, they all tend to have a high dispersive component of surface energy, which confirms the trend observed in [1].

References

[1] Li, J., Yu, X., Sciamma-O’Brien, E., et al. 2022, The Planetary Science Journal, 3, 1

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