Droplet Bouncing Research Articles

Oriented bouncing of droplets with a small Weber number on inclined one-dimensional nanoforests.

Asymmetric superhydrophobic structures with anisotropic wettability can achieve directional bouncing of droplets and thus can have applications in directional self-cleaning, liquid transportation, and heat transfer. To achieve convenient large-scale preparation of asymmetric superhydrophobic surfaces, inclined nanoforests are prepared in this work using a technique of competitive ablation polymerization, which allows the control of the inclined angles, diameters, and heights of the nanostructures. In this study, such asymmetric structures with the smallest dimension (230 nm diameter) known are achieved by a simple etching method to guide droplet unidirectional bouncing. With such nanoforests, the mechanism of droplet bouncing on their surface is investigated, and controllable droplet bouncing over a long distance is achieved using droplets with a low Weber number. The proposed structure has a promising future in directional self-cleaning, liquid transportation and heat transfer.

Dynamic behaviors and heat transfer characteristics of impacting droplets on heated superhydrophobic surfaces with randomly distributed rough structures: Numerical simulation and theoretical analysis

Due to the extensive usage of superhydrophobic surfaces, numerous studies have investigated the dynamics and heat transfer of a droplet impacting on superhydrophobic surfaces. However, previous studies did not consider the actual superhydrophobic surfaces with randomly distributed rough structures, especially so in heat transfer of droplet impacting on superhydrophobic surfaces with random rough structures. To address this issue, a multiple distribution function phase-field lattice Boltzmann model was developed to model the droplet impacting on randomly rough surfaces. After experimental validation, this model was used in the analysis of the impacting dynamics and heat transfer characteristics. The differences between actual randomly rough surface and ideal smooth surface were revealed. Herein, random rough structures significantly influence the wetting state and heat transfer of impacting droplet on solid surface. Moreover, the effects of roughness on droplet bouncing ability and the total transferred heat were evaluated. The results show that the random rough surface with smaller skewness, a kurtosis of 3.0, and a standard deviation of 0.3 μm could simultaneously promote impacting droplet to rebound from the surface and to reduce the total transferred heat. Subsequently, the predictive correlation for total transferred heat was proposed based on the roughness parameters. This work provides novel insights into the design of rough structures on functional superhydrophobic surfaces.

Visualization of Charge Dynamics when Water Droplets Bounce on a Hydrophobic Surface.

Visualizing the motion of water droplets and understanding their electrification behavior holds significance for applications related to droplet transport, self-cleaning, and anti-icing/deicing and for providing a comprehensive explanation of the solid-liquid triboelectrification mechanism. Here, by constructing microcolumnar structures on the polytetrafluoroethylene surface, a water droplet-based single electrode triboelectric nanogenerator was fabricated for visualizing charge dynamics when a water droplet bounces on a hydrophobic surface. The motion state of the water droplet is closely linked to its electrification behavior through the integration of a high-speed camera and an ammeter. The electrification behavior stemming from the bounce of the water droplet is dynamically captured in real-time. The results show that the magnitude and polarity of the electrical signal have strong dependence on the motion state of the water droplet. For instance, when a water droplet approaches or moves away from the substrate in a single direction, a unipolar electrical signal is generated. However, when the water droplet reaches its limit in the initial motion direction, it signifies a static equilibrium state, resulting in the electrical signal being at zero. Furthermore, we examine the impact of factors such as impact speed, drop contact area, contact line spreading/retraction speed, and impact angle on electrification. Finally, based on the close relationship between poly(ethylene oxide) (PEO) droplet bounce dynamics and electrical signals, the bouncing details of PEO droplets with different concentrations are tracked by electrical signals. This study digitally presents the whole process of droplet bounce in situ and provides a means for monitoring and tracking droplet movement.

Magneto-responsive wettability-switchable surfaces for in-situ large distance droplets capturing-releasing-bouncing

In this paper, superhydrophobic magnetically responsive micro-plate arrays (SMMAs) with reverse switching wettability were studied for in-situ capturing, releasing, and directional bouncing of droplets over a large distance. A novel method for producing superhydrophobic pattern on one side surface of the micro-plates by laser texturing at 90 degree bending state, created water contact angle of 151°, a rolling angle of < 10°, and a maximum surface adhesion force of 35.5 μN. Reversible switching between droplets (volume 5–40 μL) capturing with high adhesion force (high surface energy) and droplet releasing with low adhesion force were achieved spontaneously. The instantaneous response of the SMMAs to magnetic field provided a guarantee for the directional bouncing of droplets in long distance. Droplets transportation up to 40 μL, directional bouncing of 5 μL droplets with a vertical bounce height of 4.5 mm and a horizontal bounce distance of 24.7 mm have been achieved. This work provides a novel approach for flexible droplets manipulation and multifunctional operation of droplets for non-contact, remote-driven and non-destructive reagent transfer applications.

Computational fluid dynamics simulation analysis of the effect of curved rice leaves on the deposition behaviour of droplets

BackgroundAlthough previous studies on the droplet deposition behaviour of rice leaves have modelled the leaves as flat surface structures, their curved surface structures actually have a significant effect on droplet deposition.ResultsIn this paper, the statistical distribution of the coordinate parameters of rice leaves at the elongation stage was determined, computational fluid dynamics (CFD) simulation models of droplet impact on rice leaves with different curvature radii were built, and the effect of leaf curvature radius on the deposition behaviour and spreading diameter of droplets on rice leaves was studied using validated simulation models. The results showed that the average relative errors of the CFD simulation models were in the range of 2.23–9.63%. When the droplets struck the rice leaves at a speed of 4 m/s, the 50 μm droplets did not bounce within the curvature radii of 25–120 cm, the maximum spreading diameters of 200 and 500 μm droplets that just adhered to the leaves were 287 and 772 μm, respectively. The maximum spreading diameters of 50, 200, and 500 μm droplets that just split were 168, 636, and 1411 μm, respectively. As the curvature radii of the leaves increased, the maximum spreading diameter of the droplets gradually decreased, and droplet bouncing was more likely to occur. However, a special case in which no significant change in the maximum spreading diameter arose when 50 μm droplets hit a leaf with a curvature radius exceeding 50 cm.ConclusionSplitting generally occurred for large droplets with a small curvature radius and small tilt angle; bouncing generally occurred for large droplets with a large curvature radius and large tilt angle. When the droplet was small, the deposition behaviour was mostly adhesion. The change in spreading diameter after stabilisation was similar to the change in maximum spreading diameter, where the spreading diameter after stabilisation greatly increased after droplet splitting. This paper serves as a reference for the study of pesticide droplet deposition and its application in rice-plant protection.

Preparation of superhydrophobic coatings with excellent mechanical and chemical stability by one-step spraying method with selected fluorine-free modifiers

Superhydrophobic coatings have great potential for applications in daily life and industrial production. In practical applications, however, the excellent mechanical and chemical stability of superhydrophobic surfaces remains a challenge. In this paper, a one-step spraying method, simple in process and low cost, was used to prepare superhydrophobic materials. To investigate the effect of different types of non-fluorinated modifiers on the wettability of the coatings, four silane non-fluorinated modifiers, dodecyltrimethoxysilane, hetradecyltrimethoxysilane, octadecyltrimethoxysilane and polydimethylsiloxane, were selected to prepare superhydrophobic surfaces. The superhydrophobic coating modified by non-fluorinated modifier retained its superhydrophobic performance after 48 h immersion in strong acid, strong alkali and salt solution and 6 months in outdoor environment, with excellent corrosion resistance. Moreover, it showed superior abrasion resistance and durability in sandpaper abrasion and tape peeling cycles tests. The superhydrophobic coating prepared by PDMS had the best overall performance compared with other silane non-fluorinated modifiers, and the separation efficiency of the prepared superhydrophobic cotton fabric could still be maintained above 99 % after 20 oil–water separation cycles. Its water contact angle was 164.8° and sliding angle was 2.3°, and it had the highest first bouncing height after the droplet bouncing test.

Effect of film properties on droplet impact on suspended films

Understanding the dynamics and underlying mechanisms of droplet impact on suspended films is crucial for controlling droplet motion. In this study, we conducted experiments to investigate droplet impact on suspended films and examined the typical phenomena and corresponding Weber number domains. We explored the effects of changing sodium dodecyl sulfate (SDS) concentration and glycerol content on the surface tension and dynamic viscosity of the films. Additionally, we elucidated the characteristics of film deformation and droplet trajectory. An energy analysis was performed, considering the droplet kinetic energy (Ek0), surface energy increment of the film (ΔEfs), and viscous dissipation (Evis). The results demonstrate that as the SDS concentration increases, the upper critical Weber number (Wecru) between bouncing and passing decreases, while the lower critical Weber number (Wecrl) between coalescence and bouncing first decreases and then increases. For droplet bouncing, increasing the SDS concentration makes the films more susceptible to deformation, whereas increasing the glycerol content enhances film rigidity. Moreover, increasing the SDS concentration and glycerol content leads to higher energy losses, resulting in a reduction in the maximum bouncing height (hbdmax). Regarding droplet passing, the passing velocity (Vpd) increases with increasing SDS concentration. For films without SDS, Vpd increases with increasing glycerol content, while for films with SDS, Vpd decreases. The different impact modes are categorized based on the dimensionless energy parameter E* = Ek0/(ΔEfs + Evis). We have successfully predicted the critical height thresholds (Hd0crl and Hd0cru) and established a relationship of We* = f (Re*, Bo*) that aligns well with experimental results.

Velocity-Switched Droplet Rebound Direction on Anisotropic Superhydrophobic Surfaces.

Droplet well-controlled directional motion being an essential function has attracted much interest in academic and industrial applications, such as self-cleaning, micro-/nano-electro-mechanical systems, drug delivery, and heat-transferring. Conventional understanding has it that a droplet impacted on an anisotropic surface tends to bounce along the microstructural direction, which is mainly dictated by surface properties rather than initial conditions. In contrast to previous findings, it demonstrates that the direction of a droplet's rebound on an anisotropic surface can be switched by designing the initial impacting velocity. With an increase in impacting height from 2 to 10cm, the droplet successively shows a backward, vertical, and forward motion on anisotropic surfaces. Theoretical demonstrations establish that the transition of droplet bouncing on the anisotropic surface is related to its dynamic wettability during impacting process. Characterized by the liquid-solid interaction, it is demonstrated that the contact state at small and large impacting heights induces an opposite resultant force in microstructures. Furthermore, energy balance analysis reveals that the energy conversion efficiency of backward motion is almost three times as that of traditional bouncing. This work, including experiments, theoretical models, and energy balance analysis provides insight view in droplet motions on the anisotropic surfaces and opens a new way for the droplet transport.

Programmable Droplet Bouncing on Bionic Functional Surfaces for Continuous Electricity Generation

AbstractThe natural phenomenon of droplets bouncing on various surfaces holds remarkable potential for applications like water transportation, self‐cleaning, antifreezing, etc. However, achieving precisely controlled patterned droplet bouncing on functional surfaces with accurately controlled factors like bouncing velocity and trajectory in three dimensions remains a formidable challenge. In this context, a concept of bionic hydrophobic functional surfaces composed of mushroom‐like microstructures is introduced. These microstructures are crafted using the projection microstereolithography (PµSL) based 3D printing technique, subsequently coated with a hydrophobic spray. By finely adjusting the geometric attributes and inclination angles of these micromushrooms, the ability is gained to meticulously manipulate the bouncing velocity and trajectory of water droplets. The most optimal performance is demonstrated by a droplet exhibiting a maximal jumping distance and height respectively of 2.5 and 7.1 mm with 50° inclined micromushrooms. Notably, these specially designed micromushrooms orchestrate diverse behaviors in droplet bouncing, encompassing patterned bouncing, antigravity jumps, and directional water transportation. Additionally, the functional surface's adaptable self‐cleaning capability facilitates the harnessing of energy from rainfall on large surfaces, offering potential applications in realms, such as self‐cleaning mechanisms, droplet capture, water conveyance, and clean energy generation.

Phenyl-modified silica aerogels with high-temperature hydrophobicity for self-cleaning and thermal insulation under extreme circumstances

Silica aerogels tend to be employed as thermal insulating materials, however their properties are inevitable to deteriorate in humid conditions owing to the hydrophilic nature, especially above 200 °C. Herein, phenyl modified silica aerogels with superhydrophobicity, self-cleaning capacity, and ultra thermal insulation are prepared. Phenyltriethoxysilane (PTES) working as the modifier condenses with tetraethyl orthosilicate (TEOS), forming a three-dimension network containing ladder polyphenylsilsesquioxane structure, where the introduction of bulk phenyl groups decreases free energy and fabricates hierarchical regime, leading to distinctive water repellency. The water contact angles are larger than 150° with low hysteresis (less than 2°), rendering droplet bouncing and self-cleaning capacities. As the molar ratio of PTES to TEOS rises to 1, the superhydrophobicity can be preserved at temperatures as high as 500 °C. In addition, hot-steam resistance and excellent thermal insulation are achieved. When subjected to a direct impact of 200 °C steam for 5 h, the hybrid aerogel demonstrates a reversible rise of thermal conductivity around 34%. The maximum back-surface temperature keeps 55.9 °C after exposure to hot steam for 10 min. The modification can broaden the application area of silica aerogels in high-temperature thermal insulation.

Suppressing the pancake bouncing induced secondary contact on superhydrophobic surfaces via jet splash

Pancake bouncing of water droplets on superhydrophobic surfaces has been extensively studied, because the reduction in solid–liquid contact time shows great potential for self-cleaning, anti-icing, etc. However, the behavior of a pancake-bouncing droplet in the ambient air and its subsequent interaction with the underlying surface remain unrevealed, which is actually crucial for practical applications. In this Letter, we comprehensively investigate the overall dynamics of droplets on post-array superhydrophobic surfaces by extending the range of impact velocities. An unreported phenomenon was observed, whereby the retracting droplet undergoes vertical elongation and re-contacts the underlying surface following the pancake bouncing event. As the impact velocity increases, the submillimeter-scale posts notably influence the droplet splash, where tiny droplets are ejected from the edges of lateral liquid jets through the posts. Experimental results and scale analysis show that the critical Weber number for this jet splash phenomenon decreases with the post spacing and the post edge length over a certain range. The violent jet splash occurring at higher Weber numbers reduces the mass of the remaining droplet and, consequently, diminishes the diameter prior to retraction, thereby suppressing the secondary contact with the surface. Our findings are believed to provide valuable insight for the understanding and the application of the pancake bouncing effect.

Airborne hydrocarbon induced multifunctional coating towards bouncing characteristics, icing delaying, hot-water repellency, and anti-corrosion on copper

Some studies have confirmed copper coating can realize superhydrophobicity after exposure to air. However, the comprehensive characteristics of the special wettable coating such as surface energy, bouncing behavior, hot water repellency, icing delaying, and corrosion resistance are still not well understood. Here, without further chemical processing, an electrodeposition technique creates a superhydrophobic layer on a copper substrate. The wettability versus different exposure routes is investigated. As a result, the slow oxidation of Cu and adsorption of airborne hydrocarbon contribute to a low rolling angle and enhanced water droplet bouncing ability. The coating displays strong 95 °C hot water repellency, icing delaying (∼78s), and great anti-corrosion ability, which also has a high protection efficiency (98.84%) and an improved coating resistance of 2.198 × 105 Ω cm2. The multifunctional properties are attributed to the airborne hydrocarbon and the constructed hierarchical structure. This preparation process avoids complex chemical modification and it can provide a new strategy for designing multifunctional coating for surface protection on metals.

Enhancing droplets deposition on superhydrophobic plant leaves by bio-based surfactant: Experimental characterization and molecular dynamics simulations

The bouncing and splashing of pesticide droplets on the superhydrophobic plant leaves is the main reason for the low pesticide utilization rate and the main source of environmental pollution. In this study, we report a bio-based surfactant Nonyl β-D-glucopyranoside (DG) which could efficiently inhibit droplet bouncing and improve the retention and deposition on superhydrophobic plant leaves. The traditional surfactants N, N, N-trimethyl-1-dodecanaminium bromide (DTAB), and p-Octyl polyethylene glycol phenyl ether (TX-100) were used to explore the mechanism. The dynamic surface tension, surfactant aggregates, and adhesive force were investigated. Also, molecular dynamics (MD) simulations are displayed to prove the deposition mechanism. The bio-based surfactant DG with lower dynamic surface tension can diffuse and adsorb to the plant leaves rapidly. The rod-like micelles of DG interacted with the plant leaves covered with DG molecules and pinned the gas/liquid/solid three-phase contact lines to dissipate energy. This work has provided a green and efficient strategy to improve the retention of pesticide droplets on the leaves of the plant.

Directional rebound of compound droplets on asymmetric self-grown tilted mushroom-like micropillars for anti-bacterial and anti-icing applications

Directional liquid bouncing is of great significance for a variety of biological and industrial applications. Although surface engineering through 3D printing or self-assembly enables water droplets to rebound directionally, directional bouncing of compound droplets still poses a challenge due to their low surface tension. Moreover, preparation of superamphiphobic surfaces in an efficient and simple manner to accomplish this mission remains to be studied. Here, a tilted stepped mushroom-like micropillar surface (TSMMs), whose structural morphology can be created and tailored by a facile and direct femtosecond laser-induced asymmetric self-growing strategy, is designed to enable the oblique quasi-pancake bouncing of a low surface tension droplet (γ = 32 mN/m). Oblique quasi-pancake bouncing can not only reduce the droplet contact time (7 ms) but also effectively control the direction of droplet bouncing (the horizontal distance of 2.4 mm). Accompanying mechanistic analysis provides an in-depth understanding of the structure-droplet motion relationship. Finally, we demonstrate the applications of TSMMs in antibacterial and anti-icing scenarios. This work advances the investigation of directed droplet transportation, and paves new avenues in the fields of advanced biomedical and other industrial materials.

Promotion of droplet deposition, diffusion-wetting and retention on hydrophobic surfaces by nonionic star-shaped oligomeric surfactants

Massive wastage of pesticides has caused significant environmental pollution and economic loss. However, existing strategies to control loss of pesticides are complex or step-specific. Here, nonionic star-shaped surfactants that can simultaneously achieve comprehensive regulation of deposition, diffusion-wetting and retention are designed and synthesized, which greatly improve the utilization efficiency of pesticides while reducing environmental risks. Structure–activity relationships for the surfactants were elucidated, and their interactions with hydrophobic surfaces were studied in detail. The results show that the addition of nonionic star-shaped oligomeric surfactant to a solution decreased droplet bouncing, increased the diffusion-wetting area, slowed droplet evaporation; and the surfactant III-8b showed the best performance. On the basis of these results, III-8b was used as a synergist for Glyphosate-isopropylammonium 41 % AS. The biological activity test showed that the herbicidal activities of the surfactant III-8b-containing glyphosate solution against Pharbitis nil (L.) Choisy and Echinochloa crusgalli (L.) were substantially better than the activities in the absence of surfactant.

Target slinging of droplets with a flexible cantilever

AbstractControl of the directional bounce of droplets impacting solid surfaces is crucial for many agricultural and industrial applications. However, for the universal impact process of raindrops on plant leaves, little is known about how the highly coupled and complicated fluid–structure interaction controls the postimpact motion of droplets and endows the leaves with tenacious vitality. Here, we report a leaf‐like superhydrophobic cantilever to flexibly bounce droplets with well‐defined directionality and controllability. Through theoretical modeling and three‐dimensional fluid–solid coupling simulations, we find that the flexible cantilever significantly relieves the impacting forces of raindrops to reduce droplet fragmentation and enhance water repellency. The results further uncover the scaling relations of the droplet bouncing direction with respect to Weber number and cantilever stiffness. By this technique, the seemed disorganized postimpact movements of droplets are programmable and predictable, achieving the goal of where to point and where to hit automatically. This work advances the understanding of natural droplet impact phenomena, opens a new avenue for delicately controlling liquid motion in space with soft materials, and inspires a plethora of applications like soft robots to transport materials and energies, monitor plant growth as well as predict pathogen transmission in plants.

Superhydrophobic aluminum surfaces with nano-micro hierarchical composite structures: A novel and sustainable approach to corrosion protection

The unique properties of aluminum (Al) and its alloys make Al one of the most versatile, economical, and widely-used materials in various industries. However, the corrosion and leaching of Al can cause significant issues for the lifetimes of mechanical structures and machine components as well as environment and health problems. In the present study, a simple, eco-friendly, and rapid fabrication of superhydrophobic Al surfaces was introduced. The superhydrophobic Al surfaces with hierarchical composite structures combining microstructures prepared by laser texturing, the new formation of pseudo-boehmite nanostructures prepared by boiling water treatment, and low surface energy prepared by silicone oil heat treatment showed excellent corrosion resistance. The mechanism for wettability change and anti-corrosion were analyzed. The influence of laser parameters and surface modification procedures on the wettability and corrosion resistance of Al surfaces was also analyzed systematically through a series of surface characterization techniques, potentiodynamic polarization tests, and electrochemical impedance spectroscopy tests. The corrosion protection efficiency of the fabricated superhydrophobic Al surface has reached up to 99.40 % as compared with an untreated flat surface. Furthermore, the fabricated superhydrophobic surfaces show good stability even after prolonged exposure to air, fresh water, seawater, and high temperature environments. The performance of the non-wetting surfaces is demonstrated through self-cleaning, water jetting, and water droplet bouncing phenomena. This research provides a novel and sustainable approach for superhydrophobic metal surfaces and improved corrosion resistance for potential practical applications.

Impact of nanodroplets on cone-textured surfaces.

Molecular dynamics simulations have been performed to study the dynamics of nanodroplets impacting on a flat superhydrophobic surface and surfaces covered with nanocone structures. We present a panorama of nanodroplet behaviors for a wide range of impact velocities and different cone geometrics, and develop a model to predict whether a nanodroplet impacting onto cone-textured surfaces will touch the underlying substrate during impact. The advantages and disadvantages of applying nanocone structures to the solid surface are revealed by the investigations into restitution coefficient and contact time. The effects of nanocone structures on droplet bouncing dynamics are probed using momentum analysis rather than conventional energy analysis. We further demonstrate that a single Weber number is inadequate for unifying the dynamics of macroscale and nanoscale droplets on cone-textured surfaces, and propose a combined dimensionless number to address it. The extensive findings of this study carry noteworthy implications for engineering applications, such as nanoprinting and nanomedicine on functional patterned surfaces, providing fundamental support for these technologies.

Experimental analysis of droplet coalescence and transport mechanisms on a single vertical fiber

In mist filtration, fiber-based coalescers are an established form of filtering droplets contained in mist. The filtration process can be divided into different process steps, describing the impact of the droplets on fibers, the formation of fluid structures and the liquid transport. In order to investigate mechanisms inside depth filters on a microscopic level, investigations are often reduced to single fibers. In this work, the coalescence and transport mechanisms of axially distributed water droplets on a vertical fiber, subjected to gravity, are reported. This is done with the latest high-speed camera technology commercially available. Automated tracking of droplets is used for a frame-by-frame investigation of droplet position, size, and oscillation. Coalescence mechanisms describe the process of fluid formation. The first observed coalescence mechanism is identified by the coalescence of droplets contained in mist with an adhering droplet at the fiber. The second coalescence mechanism describes the coalescence of two closely spaced sessile droplets on a fiber. As a result, the newly formed droplet oscillates and can begin to drain. Furthermore, the coalescence process of a draining and sessile droplet is reported. Both the draining droplet and the second droplet involved in the coalescence event can be subject to oscillation. The given temporal high-resolution information about the droplet position and deformation improves the understanding of droplet coalescence on fibers and by that also its influence on transport processes and therefore droplet drainage. Observed transport mechanisms which take part in the drainage process are gravitational draining, droplet bouncing, and droplet sweeping.

The Criterion of Supercooled Bionic Lotus Surfaces Repelling Impacting Droplets for Anti‐Icing Engineering

AbstractIcephobic material is of great importance in power transportation, communication, aerospace, and so on. Bionic lotus superhydrophobic surfaces show good application prospects in anti‐icing by repelling impacting droplets. However, the boundary (criterion) between droplet bounce and deposition on superhydrophobic surface under cold freezing rain is unclear. Here, from the view of statistics, the boundary and internal heat transfer mechanism of the droplet bounce, pinning, and three kinds of deposition including icing at later, early retraction, and spread. are clarified Droplet viscosity increase reduces droplet contact with surface and inhibited splash at high We. Surfaces with temperature above −20.6 °C showed 100% droplet bounce after impact on We = 64.7, and the probability of water adhesion and ice nucleation decreases to ≈0%, resulting in completely anti‐icing. Droplet bounce transition mainly ascribe to the decrease retraction driven force caused by interface freezing and transition temperature increases approximately linearly from −25.9 to −21.1 °C within 21.6 &lt; We &lt; 75.5. Ice nuclei brought by condensation in humid environment (60–100 RH%) further cause droplet eccentric retraction and transition temperature increases to −6 to −10 °C. The fundamental understanding of droplet behaviors on supercooled superhydrophobic surface is beneficial for icephobic surfaces applications.