arXiv subjects

Adis Husić

Publications and source records attributed to Adis Husić.

2 recordsLinked to original sources

arXiv2026

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

The organic haze particles on Titan play important roles in atmospheric cloud formation and aerosol-lake interactions. These processes are strongly influenced by the surface energy of the haze particles, which controls cohesion and wetting behavior. This study presents a comparative analysis of 32 laboratory-produced haze analog samples ("tholins") synthesized across three laboratories. Using contact angle measurements, we determine the total surface energy and its dispersive and polar components for all samples, systematically evaluating the effects of substrate choice, air exposure, initial N2/CH4 gas mixture, and experimental setup. We find that tholin samples exhibit minimal substrate dependence, whereas exposure to ambient air substantially modifies the surface chemistry, altering the balance between dispersive and polar components. Thus, future Titan-relevant surface property measurements may use any substrate but must keep samples pristine. Surface energies vary weakly across methane concentrations, from 1-10% CH4 in N2, indicating that Titan's hazes formed at different altitudes should exhibit broadly similar cohesiveness. In contrast, experimental conditions such as gas exposure time and energy source produce the dominant differences in surface energy, driven largely by variations in polar components. Despite these differences, tholin samples exhibit high dispersive components, implying that Titan's hazes should act as efficient cloud condensation nuclei for hydrocarbon clouds and should generally sink into Titan's lakes. Given observed ethane ice clouds, we conclude that cold plasma tholins may be better physical analogs for Titan's hazes than samples produced with far-ultraviolet irradiation, though intrinsic surface energies of UV tholins remain uncertain due to film thickness limitations.

astro-ph.EP↗

arXiv2026

Feeling the Pressure: Effects of Formation Pressure on the Physical Properties of Titan Haze Analogs

The Cassini-Huygens mission detected large negative ions in Titan's ionosphere at pressures as low as $10^{-6}$ torr. These ions ultimately polymerize to form Titan's complex organic haze particles, which are observed throughout the atmosphere and potentially on the surface. Laboratory analogs of these hazes, known as tholins, have been used to study Titan's aerosols; however, most are produced at much higher pressures. The influence of formation pressures on key physical properties -- such as particle size, density, surface energy, and mechanical strength -- remains poorly constrained. These properties govern the haze's aggregation efficiency, radiative behavior, and surface-atmosphere interactions, shaping Titan's climate and surface. To investigate the effects of formation pressure, we generate tholins using a newly developed cold plasma discharge system. A 95% nitrogen and 5% methane gas mixture is exposed to plasma at two pressures, 1 torr and 0.125 torr. For both samples, we measure the production rate, particle size, morphology, density, surface free energy, Young's modulus, and nanoindentation hardness. While particle size, morphology, surface energy, and Young's modulus are similar across both pressures, tholins produced at lower pressure exhibited a threefold lower production rate, but a higher density and nanoindentation hardness. These variations likely reflect pressure-dependent changes in chemical structure, porosity, and mechanical strength. Because Titan's hazes form at much lower pressures than investigated here, actual haze particles are potentially even denser and mechanically stronger than our analogs, with implications for aerosol aggregation, aeolian and fluvial transport, and surface modification on Titan.

astro-ph.EP↗