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When a droplet off-center impacts a macro-ridge, it may split into two asymmetric fragments, i.e., the smaller part (SP) and larger part (LP), which then exhibit asymmetric spreading and receding phenomena. Using lattice Boltzmann method simulations, the dynamics of a droplet off-center impacting a hydrophobic surface are explored for the first time. Influences of the off-center distance, the impact Weber number, and the surface wettability on the impact outcomes and the contact time are elucidated, and the impact regime is established. Six impact outcomes are discovered as off-center distance changes, which are dependent on the interaction force between the droplet and the surface. The effect of the off-center distance and the Weber numbers on the spreading and the receding dynamics of the SP is more obvious than that of the LP, due to the fact that adhesion of the ridge on the LP can be negligible compared to the inertial force and the surface tension. The contact time is closely related to the impact outcomes, that is, when the impact outcome is type 1 (SP and LP separate rebound), the contact time can be significantly reduced compared with that on the flat hydrophobic surface, due to the fact that the ridge can reduce the asymmetry of a liquid film and the receding distance in this case; while when the impact outcome is type 6 (SP and LP completely coalescence and rebound), the contact time cannot be reduced. This work extends the fundamental knowledge of off-center impact and provides inspiration for the efficient reduction in the contact time. [ABSTRACT FROM AUTHOR]

In this study, we experimentally explored the impact outcomes of droplets under a wide range of Weber numbers (0.2 ≤ We ≤ 200) and contact angles (91° ≤ θ ≤ 162°). Five impact outcomes were identified: deposition, rebound, partial rebound, receding breakup, and prompt splash. Compared to the literature, we gathered more comprehensive data on the impact outcomes at various contact angles, which were then organized into a complete phase diagram. Furthermore, we corroborated the accuracy of these outcomes through comparisons with other studies. We conducted a comprehensive analysis of the associated phenomena and underlying mechanisms of these outcomes. By introducing the concept of surface hysteresis energy, we also proposed identification criteria for partial rebound. This innovative approach provides an important reference for further understanding of droplet impact behavior and provides guidance for future research in this field. [ABSTRACT FROM AUTHOR]

Taking the preparation of electrode materials of supercapacitors, the study of properties and the performance of assembled asymmetric supercapacitors as the core contents, and improving the electrochemical performance of supercapacitors as the main purpose, the in-situ polymerization method was used to prepare carboxylated multi-walled carbon nanotubes (PI-MWCNTs) grafted polyimide solution, which is used as the precursor of nitrogen-doped carbon to realize the growth of composites on the surface of carbon cloth and as electrode material.Manganese dioxide-carbon cloth (MnO2-CC) as the positive electrode, Polyimide-carbon cloth grafted with multi-walled carbon nanotubes as negative electrode (PI-MWCNTs-CC), build asymmetric supercapacitors. The structure and electrochemical properties of the electrode materials were characterized by scanning electron microscopy, raman spectroscopy, surface area and pore size testing, X line photoelectron spectroscopy, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. According to the study, when the scan rate is 20 mV/s, asymmetric capacitor potential window can be increased to 1.3 V and its volume specific capacity is 1.80 F/cm3.When the power density is 14.08 mW/cm3, the energy density can reach up to 0.423 mWh/cm3.

Coalescence-induced droplet jumping on superhydrophobic surfaces has been observed at microscale and even nanoscale. The enhancement in jumping velocity of coalescing droplets is crucial for condensation heat transfer enhancement, antiicing, self-cleaning, and so forth. However, the research on how to acquire a higher jumping velocity is really very limited. In this paper, we use molecular dynamics simulations to study the coalescence-induced jumping of two equally sized nanodroplets on chemically heterogeneous surfaces composed of alternating stripes with different hydrophobicity. We show that the jumping velocity is closely related to the stripe width and wettability contrast, and it can even exceed that on an ideal superhydrophobic surface with 180 [degrees] contact angle when the striped surfaces are properly designed. We also demonstrate that there is always an optimal stripe width yielding the maximum jumping velocity, whereas its value is independent of the wettability contrast. We reveal that the dominant factor to determine the jumping velocity is the apparent contact angle of equilibrated droplets over heterogeneous surfaces for small stripe widths; it changes to the time of liquid bridges impacting surfaces for moderate stripe widths and to the contact area between equilibrated droplets and relatively hydrophobic stripes for large stripe widths. We believe the present simulations can provide useful guidance to design self-jumping superhydrophobic surfaces. Key words: mixed-wettability, superhydrophobic surfaces, coalescence, jumping velocity, molecular dynamics simulations. Les sauts de gouttelettes induits par coalescence sur une surface super-hydrophobe s'observent aux echelles micro et nano. L'accroissement de la vitesse de saut des gouttelettes se fusionnant est cruciale pour l'augmentation du transfert de chaleur par condensation, pour l'antigivrage, l'auto-nettoyage, etc. Cependant, il n'y a que tres peu de recherche sur le moyen d'augmenter la vitesse de saut. Nous utilisons ici des simulations de dynamique moleculaire pour etudier le sautillement, induit par leur fusion, de deux nano-gouttelettes de meme grosseur sur des surfaces chimiquement heterogenes composees de bandes alternees de differente hydrophobicite. Nous montrons que la vitesse de saut est etroitement reliee a la largeur de ces bandes et du contraste de mouillabilite et qu'elle peut meme exceder celle sur une surface superhydrophobe continue ideale avec un angle de surface de 180 [degrees], a condition que les surfaces striees soient concues de facon appropriees. Nous annoncons aussi qu'il y a une largeur de bande optimale produisant une vitesse de saut maximale, et que sa valeur est independante du contraste de mouillabilite. Nous revelons que, sur les surfaces heterogenes avec des bandes de petites largeurs, le facteur dominant pour determiner la vitesse de saut est l'angle de contact apparent des gouttelettes en equilibre, mais pour des bandes de largeur moyenne, ce facteur dominant devient le temps du pont liquide impactant la surface, alors que pour des bandes de grande largeur, il devient la surface de contact entre les gouttelettes equilibrees et les bandes relativement hydrophobes. Nous croyons que les resultats de ces simulations fourniront des guides utiles dans la conception des surfaces super-hydrophobes auto-sautillantes. [Traduit par la Redaction] Mots-cles : mouillabilite mixte, super-hydrophobe, coalescence/fusion, vitesse de saut, simulations de dynamique moleculaire., 1. Introduction Coalescence-induced droplet jumping on superhydrophobic surfaces was first discovered by Boreyko and Chen in 2009 [1]. Over the past decade, this phenomenon has received more and more attention [...]