Effects of Free Surface Evaporation on Water Nanodroplet Wetting Kinetics: A Molecular Dynamics Study

Abstract

The wetting kinetics of a water nanodroplet undergoing evaporation on a heated gold substrate were examined using molecular dynamics (MD) simulations. Various substrate and initial droplet temperatures were used to obtain different evaporation rates. The water molecule absorption-desorption behavior was analyzed in the vicinity of the contact line region to show the microscopic details of the spreading-evaporating droplet. Increasing substrate temperatures greatly affected the dynamic wetting process, while the initial water droplet temperature had very little effect. The effects of droplet size and substrate wettability on the droplet spreading-evaporating process were also examined. The radius versus time curves agree well with molecular kinetics theory (MKT) for spreading without evaporation but differ from MKT when the spreading induced evaporation. The enhancement of the wetting kinetics by the evaporation can be attributed to the reduction of the liquid-vapor surface tension and the increased water molecule motion in the contact line region and in the bulk droplet.

Effect of Solid–Liquid Interactions on Substrate Wettability and Dynamic Spreading of Nanodroplets: A Molecular Dynamics Study

“…After the reshape stage, the spreading gradually slows down and eventually stops for the cases with low ε O–Pb (≤3 × ε O–O ), indicating an equilibrium state; for cases with higher ε O–Pb (≥4 × ε O–O ), the spreading continues with a late-time scaling of R ∼ t 1/3.5 , regardless of ε O–Pb . Similar trends have also been reported in the previous studies. ,,, In a set of simulations with a similar setting to our work, the calculated spreading of a cylindrical water droplet on Au surfaces , gives an exponent of about 0.25 for the late spreading stage, which is close to our result (about 0.28). The exponent of 0.28 is somewhat larger than asymptotic prediction (0.2) based on the linearized version of the MKT.…”

“…Influencing both the forces at the molecular scale, solid–liquid interactions play a crucial role in spreading dynamics. ,,− Therefore, it is vitally important to investigate the effects of solid–liquid interactions on the spreading of liquid on the solid surface. However, even though the spreading of liquid droplets on solid substrates has been extensively studied, − ,,− a fundamental understanding of how the solid–liquid interactions control the substrate hydrophilicity and the spreading phenomena is still lacking.…”

“…6,31 In the estimation of the spreading exponent, many studies have simply fitted the R−t relation without considering the different stages of spreading, 6,15,17,19,21,22,25,31 which may have affected the accuracy of the results to some extent. A recent numerical study on water droplet spreading on a gold substrate 20 characterized the whole spreading process into two separate stages, and the corresponding exponents were obtained; however, the rationality of separation was not explained. Another study on the spreading dynamics of a water nanodrop on graphene 17 showed that solid−liquid interactions affect the spreading process and that the spreading rates are smaller in the beginning and at the end of spreading, while the explored range of solid−liquid interaction strength in this research was limited.…”

Effects of Solid Fraction on Droplet Wetting and Vapor Condensation: A Molecular Dynamic Simulation Study

“…Current studies are not limited at the macro-scale level, and the rapid development of molecular simulation provides a valuable research instrument in investigating numerous interfacial phenomena at the microscale level. However, a significant amount of attention focused on the wetting process of droplets on various textured surfaces, − there is paucity of studies examining a simulation study of a condensation process on patterned surfaces. There are several gaps in droplet formation, growth, and coalescence processes on textured surfaces when compared with those on a smooth surface.…”

Molecular Dynamics Analysis on the Wetting Properties of R32, R1234yf, and Their Mixture on Pillar-Type Nanostructured Substrates

“…), change solid properties (adding structures, − surface coating, etc. ), and external physical field (electric field, magnetic field, thermal field, etc.). Different methods have their own applicable scenarios and limitations.…”