A Cross-Laboratory Comparison Study of Titan Haze Analogs: Surface\n Energy

In Titan's nitrogen-methane atmosphere, photochemistry leads to the\nproduction of complex organic particles, forming Titan's thick haze layers.\nLaboratory-produced aerosol analogs, or "tholins", are produced in a number of\nlaboratories; however, most previous studies have investigated analogs produced\nby only one laboratory rather than a systematic, comparative analysis. In this\nstudy, we performed a comparative study of an important material property, the\nsurface energy, of seven tholin samples produced in three independent\nlaboratories under a broad range of experimental conditions, and explored their\ncommonalities and differences. All seven tholin samples are found to have high\nsurface energies, and are therefore highly cohesive. Thus, if the surface\nsediments on Titan are similar to tholins, future missions such as Dragonfly\nwill likely encounter sticky sediments. We also identified a commonality\nbetween all the tholin samples: a high dispersive (non-polar) surface energy\ncomponent of at least 30 mJ/m2. This common property could be shared by the\nactual haze particles on Titan as well. Given that the most abundant species\ninteracting with the haze on Titan (methane, ethane, and nitrogen) are\nnon-polar in nature, the dispersive surface energy component of the haze\nparticles could be a determinant factor in condensate-haze and haze-lake\nliquids interactions on Titan. With this common trait of tholin samples, we\nconfirmed the findings of a previous study by Yu et al. (2020) that haze\nparticles are likely good cloud condensation nuclei (CCN) for methane and\nethane clouds and would likely be completely wetted by the hydrocarbon lakes on\nTitan.\n