Contact line pinning as a method to control deposit morphology during the evaporation of a TiO2 nanofluid droplet
N.B. Miskiv1, M.M. Vasiliev1, N.A. Nazarov1, A.M. Kargina1, V.S. Sulyaeva2, S.V. Starinskiy1, E.M. Starinskaya1
1Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences (SB RAS), Novosibirsk, Russia
2Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences (SB RAS), Novosibirsk, Russia
Keywords: contact line pinning, droplet evaporation, deposit morphology, nanofluid, titanium dioxide (TiO2)
Abstract
This study experimentally investigates the influence of silicon substrate temperature and titanium dioxide (TiO2) nanofluid concentration on the dynamics of the three-phase contact line and the morphology of deposits formed during droplet evaporation. The nanofluid was produced via pulsed laser ablation in liquid. Mass concentrations of 8.7 × 10⁻⁴ wt% and 2.1 × 10⁻³ wt% were examined at substrate temperatures ranging from 80 to 140 °C. It was found that the addition of TiO2 nanoparticles extends the duration of the three-phase contact line pinning stage. Consequently, the contact line diameter changes in a stepwise manner, leading to the formation of concentric ring structures of deposited material with a characteristic spacing. At surface temperatures of 80 and 100 °C, radial capillary transport dominates, resulting in the formation of a "coffee ring." Increasing the surface temperature to 120°C initiates nucleate boiling, which expands the deposition zone, whereas at 140°C, fully developed nucleate boiling disrupts steady particle transport and leads to a redistribution of the deposit.
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