Dynamic Behavior Of Water Droplet Research Articles

Study on microstructure evolution of waxy crude oil emulsions under dynamic cooling conditions.

A rheo-microscopy in situ synchronous measurement system was utilized to investigate the dynamic behavior of water droplets in W/O waxy crude oil emulsions subjected to dynamic cooling conditions, the microstructural evolution of water droplets aggregates can be categorized into three stages based on the various forms of wax crystals. The results show that under the joint action of wax crystals and water droplets, the water droplets aggregation trend and complexity in the system are negatively correlated with the changes of temperature and shear rate, and the water droplets movement behavior is positively correlated with the changes of temperature and shear rate. As the temperature decreases, the minimum edge distance of water droplets decreases by a maximum of 32.1%, the specific surface area (SA) decreases by a maximum of 12.0%, and the fractal dimension increases by a maximum of 11.7%. As the shear rate increases, the minimum edge distance of water droplets increases by up to 27.9%, the specific surface area (SA) increases by up to 10.1%, and the fractal dimension decreases by up to 8.5%. Additionally, an analysis is conducted on the collision aggregation behavior of water droplets in shear flow field based on population balance theory.

Fabrication of bioinspired closed chute structure on TC4 surface by double laser beam ablation for enhanced dynamic anti-icing performance

The dynamic behavior of water droplets plays an important role in anti-icing performance, as when they impact on superhydrophobic surfaces, the rebound process effectively removes potential ice crystal nuclei on the surface, thereby reducing ice condensation and accumulation, ultimately preventing ice formation. In this study, inspired by the cuticle structure of springtails and the tilted arrangement of pigeon feathers, a bionic superhydrophobic surface with closed chute structure is proposed. The closed chute structure reduces the adhesion force between the surface and water droplets, enhancing directional rebounding ability and accelerating water droplets' separation from the surface for enhanced anti-icing performance. Considering the morphology of hierarchical closed structures is difficult to be regulated by single laser beam ablation, the superhydrophobic surface with closed chute structure is successfully fabricated by double laser beam ablation. This method optimizes the spatial distribution of the laser energy field by adjusting the rotation angle of the half-wave plate (HWP). By combining the analysis of micromorphology, elemental distribution, dynamic and static anti-icing tests etc., it is verified that the superhydrophobic surface with closed chute structure can improve the dynamic anti-icing performance, which provides a new method for anti-icing design in engineering field.

Effect of temperature difference between impinging droplet and cold superhydrophobic surface on its dynamic behavior

The phenomenon of water droplets impacting on cold surfaces and freezing is common in various fields and has numerous detrimental effects. Meanwhile, superhydrophobic surfaces have received a lot of attention in terms of preventing icing. Therefore, it is important to investigate the dynamic behavior of water droplets impacting on superhydrophobic surfaces in a supercooled environment under different temperature conditions in order to prevent icing. In this study, the dynamic behavior of water droplets impacting on superhydrophobic surfaces in a supercooled environment is visualized using a high-speed camera, and the effect of the temperature difference between the droplet and the cold surface on the dynamic behavior of the impacting droplet is emphatically investigated. The dynamic characteristics of the droplet were also analysed in terms of dimensionless contact diameter, dimensionless droplet height, contact time and energy balance. The results show that the change in properties of the droplet is mainly reflected in the change in viscosity. At low Weber number, the change in viscosity has little effect on the dimensionless contact diameter and contact time but has a significant effect on the dimensionless height of the droplet during retraction. Of particular note is the fact that when the droplet temperature is constant, a decrease in the surface temperature leads to a significant slowing down of the droplet retraction process on the superhydrophobic surface and a significant increase in the contact time. However, a phenomenon contrary to intuition has been observed, namely that a similar situation occurs with increasing droplet temperature when the surface temperature is constant. This behaviour of the droplets is related to the possible existence of liquid-phase condensation processes in the microstructure, and we have also analysed theoretically the conditions under which condensation occurs. This study could contribute to the development of anti-icing technology.

Anti-Icing Mechanism for a Novel Slippery Aluminum Stranded Conductor.

The icing of transmission conductor seriously threatens the safe operation of power grids. Slippery lubricant-infused porous surface (SLIPS) has shown great potential for anti-icing applications. However, aluminum stranded conductors have complex surfaces, and the current SLIPSs are almost prepared and studied on small flat plates. Herein, the construction of SLIPS on the conductor was realized through anodic oxidation and the anti-icing mechanism of the slippery conductor was studied. Compared to the untreated conductor, the SLIPS-conductor reduces the icing weight by 77% in the glaze icing test and shows very low ice-adhesion strength (7.0 kPa). The excellent anti-icing performance of the slippery conductor is attributed to the droplet impact dynamics, icing delay, and lubricant stability. The dynamic behavior of water droplets is most affected by the complex shape of the conductor surface. Specifically, the impact of the droplet on the conductor surface is asymmetric and the droplet can slide along the depression in low-temperature and high-humidity environments. The stable lubricant of SLIPS increases both the nucleation energy barriers and the heat transfer resistance, which greatly delays the freezing time of droplets. Besides, the nanoporous substrate, the compatibility of the substrate with the lubricant, and the lubricant characteristics contribute to the lubricant stability. This work provides theoretical and experimental guidance on anti-icing strategies for transmission lines.

Water-Droplet Impact and Sliding Behaviors on Slippery Surfaces with Various Weber Numbers and Surface Inclinations

The dynamic behaviors of water droplets on a slippery surface are significant to practical anti-icing applications. Herein, the impact and sliding behavior of water droplets on lubricant-infused surfaces (LISs) were investigated with a high-speed camera. LISs were prepared by infusing perfluoropolyether oils into anodized porous surfaces. The results show that the maximum spreading diameter and retraction velocity of the impact droplet increased with the We number. For LIS-100, the spreading factor at 2.5 ms increased from 2.00 to 3.88 with We increasing from 30 to 267. Low-viscosity lubricant facilitated the retraction speed and rebound of droplet impact on the surface, while high-viscosity lubricant contributed to the lubricant stability of the LIS. Additionally, high inclination angle (θ) facilitated the rapid shedding of water droplets on the surface. The velocity increased rapidly from 1.04 to 4.66 mm/s with θ increasing from 15° to 45°. The LIS prepared with low-viscosity lubricant had a high sliding velocity, and the sliding velocity of water droplets on LIS-100 was about seven times faster than that on LIS-104. This work reveals the impacting law of water droplets on LISs and provides useful information for the design of LISs under drop impact conditions.

Magnetocontrollable droplet mobility on liquid crystal-infused porous surfaces.

Supplementary material (further details of the stability of LCIPS against water-induced dewetting, the interfacial tension and contact angle measurement using a goniometer, the estimation of the thickness of LC wrapping layer at air-water interface on droplets, SEM measurements, the average sliding velocity of a water droplet on 5CB, E7, silicone oil, and mineral oil films with and without a magnetic field, representative force diagram (Fd versus time) of a 3-µL water droplet moving at a speed of 0.1 mm/s on a nematic 8CB film, Fdynamic acting on 3 µL water droplets moving at speeds of 0.1-1 mm/s on an isotropic 8CB film, the calculated magnetic coherence length as a function of the magnitude of the magnetic field applied to the nematic LCIPS, and the apparent advancing and receding contact angles of a moving water droplet on nematic LCIPS as a function of time, and polarized light micrographs (top view) of a nematic 8CB film between two DMOAP-functionalized glass slides before and after applying a horizontal magnetic field) is available in the online version of this article at 10.1007/s12274-022-5318-y.

Charge-Dipole Attraction as a Surface Interaction between Water Droplets Immersed in Organic Phases.

The dynamic behavior of emulsion droplets during their interactions with one another or with solid surfaces plays a paramount role in their ultimate stability in various applications. While the interaction of oil droplets through a surrounding aqueous phase is well understood, recent studies on the interaction of water droplets through a surrounding pure organic phase showed the presence of an unexplained attraction between water droplets at relatively long ranges. In this research study, we propose fixed-surface-charge-bulk-dipole attraction as a new interaction force between water-in-oil droplets and then derive an equation for its disjoining pressure. The behavior of water droplets in the presence and absence of this charge-dipole interaction was numerically quantified using the Stokes-Reynolds-Young-Laplace model and compared to the experimental data. Numerically calculated net force curves are in excellent agreement with experimental data from the literature when charge-dipole attraction is included, while they deviate in its absence. In addition, the water droplet and thin oil film profiles in the presence and absence of charge-dipole attraction were calculated and compared. This research indicates that charge-dipole attraction can adequately explain the mysterious force observed in some studies, which demonstrates its unexplored potential to capture the physical properties and dynamic behavior of water droplets in organic phases with useful implications to unravel unidentified interactions between emulsion droplets in different industries.

Dynamic behaviors of water droplets on superhydrophobic polyester films and woven and knitted fabrics

In this study, the behaviors of water droplets on superhydrophobic polyester (PET) films as well as on woven and knitted fabrics with different surface microstructures were analyzed. The water droplet volume, height of release ( h), and surface inclination were modified to study the dynamic behavior of water droplets using a pressure balance and the Weber number ( We). The droplet volume did not affect the static contact angle. However, the shedding and sliding angles decreased with an increase in droplet volume. The water droplets rebounded on the surface of the superhydrophobic PET films with nano-roughness regardless of the surface inclination angle or h. However, the water droplets with h = 10 cm were pinned on the horizontal surfaces of the woven and knitted fabrics with micro-sized pores, where the dynamic pressure ( Pd) exceeded the capillary pressure. On an inclined surface, the water droplets rebounded on the surface of the woven fabric, owing to a decrease in Pd and an increase in the surface inclination angle. However, on the surface of the knitted fabric, pinning was observed even when the surface was tilted, regardless of the inclination angle. The sliding velocity of the droplets after rebound decreased in the following order: film, knitted fabric, woven fabric. With an increase in the inclination angle of the surface and the droplet volume, the sliding velocity increased, which was accompanied by a decrease in vertical impact velocity ( V) and an increase in the gravitational force. In terms of We, the droplets with a low We rebounded on all superhydrophobic surfaces, whereas the droplets with a high We were pinned on the surface of the woven and knitted fabrics.

Study of superhydrophobicity according to surface structure of knitted fabrics

This study seeks to analyze the effect of geometric structures of weft-knitted fabrics on superhydrophobicity and the dynamic behavior of water droplets. A flat knitting machine with different stitch patterns was used to prepare 100% polyester knitted fabrics. For the superhydrophobic surface, nano-roughness through alkaline treatment and a hydrophobic coating were introduced on prepared knitted fabrics. To analyze micro-roughness, pore size, cover factor, surface roughness, and air permeability were measured. Surface wettability was evaluated by contact and shedding angle measurements, and the dynamic behavior of droplets. Micro-roughness was greater in the order of tuck, purl, and plain jersey stitch patterns with a small cover factor and large pore size. In addition, tuck and purl stitches showed differences in surface roughness according to the wale and course directions. Nano-roughness was discernible as the alkaline treatment time increased. Following an evaluation of the wettability, the purl stitches exhibited a contact angle of 150° or more with only the hydrophobic coating. After imparting nano-roughness by alkaline treatment, the contact angle was more than 150° in all the samples. In the case of shedding angle, the tuck and purl stitches showed differences according to the course and wale directions. The shedding angle was lower when the roughness was high and the ridge and the droplet sliding directions were parallel. This difference decreased as the nano-roughness increased according to the alkaline treatment time. An evaluation of the dynamic behavior of water droplets on the superhydrophobic knitted fabric showed that rebound behavior appeared in all the samples on the horizontal surface, when the water droplet was small. However, with large droplets, the rebound behavior appeared only in purl stitches. Meanwhile, on the surface inclined at 15°, rebound behavior was observed in the tuck and purl stitches, with the tuck stitches rebounding faster in the wale direction and the purl stitches in the course direction regardless of the droplet volume. The plain jersey stitches showed pinning behavior after water droplets fell on the surface. Therefore, it is important not only to introduce nano-roughness but also properly to form geometrical micro-roughness of knitted fabric with pores and loops to induce rebound behavior of water droplets.

Dynamic behaviors of water droplet moving on surfaces with different wettability driven by airflow

The movement and deformation of droplet is widely applied in many fields. In this study, to investigate the dynamics of droplets moving on surfaces with different wettability driven by airflow, a series of experiments are conducted by using a high-speed camera, under conditions of airflow speeds increased from 0m/s to 22.2m/s with the same pattern per case, droplet volume varied from 20 to 80 μL, and different wettability surfaces (aluminum, PMMA, titanium, PTFE, PAL). Based on the observation of experiments, the change of the morphology of the droplet motion is divided into 4 stages. Stage I: Droplet oscillates at the original position and its wetting line does not move. Stage II: The droplet still oscillates and its wetting line slightly moves on the surface. Stage III: Droplet deforms dramatically and accelerates forward, and its wetting line elongates sharply. Stage IV: Several sub-droplets are split from the mother droplet. The droplet separation usually occurs after its wetting length reaches the extremum value. Specifically, the droplet separation is not observed on the PTFE and PAL surface, and the four stages of droplet motion reduce to three in these cases. According to the observation, droplet shapes during their movement are classified into four categories including compact, tail formation, film formation, and droplet separation. The relationship between the critical airflow speed at which the wetting line begins to move and the droplet diameter is studied, corresponding to different surfaces. To provide an insight into the phenomenon of dynamics and deformation of airflow-driven sessile droplet spreading, quantitative analysis of the characteristic parameters of the droplet including the wetting length, the dynamic contact angle, and the velocity of the center of droplet gravity are conducted. It is shown that the wetting length ratio of droplets moving on different surfaces varied in the range from 0 to 3.63. The maximum value of the difference between cosines of the upstream contact angle and downstream contact angle usually approaches the cosines of the receding contact angle and the advancing contact angle at the end of Stage II. This study provides experimental reference data for the study of the droplet motion driven by airflow.

Bioinspired Topological Surfaces for Mitigating Water, Thermal and Energy Crises

ConspectusThe remarkable advances in technical and industrial fields have stimulated the world’s economic prosperity and population growth while also exacerbating the global water, thermal, and energy crises. To mitigate these crises, numerous large-scale devices have been constructed to harvest water, dissipate heat, and generate energy, yet they still encounter several bottlenecks, such as bulky size and climatic and/or geographic constraints. In contrast, miniature and portable water-based devices have demonstrated their tremendous potential in water harvesting and thermal/energy management due to the ubiquitous existence, large phase-change latent heat, and abundant kinetic energy of water. Owing to the strong dependence of their performance on the interfacial interactions between water and a surface, designing novel surface topology, in both physical and chemical aspects, is of practical importance to impart them with the ability to control the interfacial interaction/exchange among water, heat, and energy in an efficient, precise, and programmable manner.Developing novel, functional, and topological surfaces can involve learning from nature because many living organisms have evolved functional surface topologies to fundamentally tailor their interactions with liquids to survive in complicated and harsh environments. Although great progress has been made in bioinspired topological surfaces, two major bottlenecks consisting of a fundamental understanding and practical applications remain elusive. From the perspective of a fundamental understanding, the principles by which the surface topology of an organism controls the dynamic behavior of water droplets need to be deciphered comprehensively. From the perspective of practical applications, rationally designing surface topologies to achieve multifunctionality in industrial processes, especially in complex and harsh conditions, is of great importance. In this Account, we systematically review our recent progress in promoting bioinspired topological surfaces toward practical applications. We start with a fundamental investigation of various topological surfaces for rapid droplet bouncing facilitated by specific surface structures or a slippery liquid film. Subsequently, we introduce different surface topology designs for directional liquid transport. On the basis of these fundamental understandings, we further demonstrate their representative practical applications, including water harvesting, thermal management, and energy conversion. Finally, we offer a brief summary and perspectives on the development of novel bioinspired topological surfaces.

Surface topography effects on dynamic behavior of water droplet over a micro-structured surface using an improved-VOF based lattice Boltzmann method

A volume of fluid-based lattice Boltzmann method (VOF-LBM) is developed, using the open-source parallel lattice Boltzmann solver library (Palabos) to study the wettability of solid surfaces and include the droplets’ dynamic behavior. This improves the accuracy and diminishes limitations on the density and viscosity ratios and the outcoming spurious velocities. An experimental study is performed, and the numerical results are verified through comparison with experimental data. Next, to design novel hydrophobic surfaces with pillar structures, the effect of different pillar patterns and topographies on the contact angle of water droplets and the droplet motion over an inclined surface are investigated. Hydrophobic micro-pillar surfaces are designed to enhance the ease of droplets movement on the slope. The effect of contact angle, wetted area, and surface energy on the sliding behavior of droplets is examined and presented. Results indicate that the new VOF-LBM method can simulate high density and viscosity ratios (1000 and 1.81×10-2 respectively), allowing real-world problems to be analyzed with appropriate accuracy. This reduces the spurious velocities produced at the fluids interface by 19 times compared to the Shan and Chen method. Results demonstrate that the contact angle of the water droplet on the surface with a contact angle of 115° can reach 160° by changing the surface topography. Also, a hydrophobic micro-pillar surface is designed in which the droplet moves nearly 12% faster than the flat surface.

Study on dynamic behavior of water droplet impacting on super-hydrophobic surface with micro-pillar structures by VOF method

Super-hydrophobic surfaces have been widely developed due to their unique properties, such as adhesion reduction and corrosion inhibition. It is of great significance to explore droplet dynamic process when impacting on super-hydrophobic surface, which can contribute to understanding the mechanism of super-hydrophobicity, and designing self-cleaning surfaces with ultralow adhesion and excellent corrosion resistance. Herein, three-dimensional (3D) numerical model was developed to study the droplet dynamic behaviors on super-hydrophobic NiTi surface. The volume of fluid (VOF) method was carried out to track the multi-phase flow interface and then predict droplet shape evolution during the spreading, retraction, and rebounding stages. In particular, the compression- and stretch-rebounding behaviors were investigated in detail. Based on the results of numerical simulation, the emphasis was placed on the relationship between droplet shape transformation and internal velocity/pressure distribution, revealing the mechanism of droplet morphological evolution during the impingement process. Then the experimental investigations were conducted on the planar and super-hydrophobic NiTi surfaces at different impact velocities to further verify the simulation models. It is indicated that the falling droplet would directly deposit on the planar surface, while it could fully rebound off the pillar-patterned super-hydrophobic surface. Moreover, the motion mechanism of droplet impacting on super-hydrophobic surface was elaborated, which can provide an essential instruction to effectively reduce liquid adhesion and improve anticorrosion ability for the NiTi material.

Wetting and anti-fouling properties of groove-like microstructured surfaces for architectural ceramics

Contaminants on architectural ceramics have become a major problem in people's lives. Interestingly, superhydrophobic surfaces offer a new avenue for anti-fouling applications. In this work, a UV-laser process for constructing groove-like microstructures on architectural ceramics and subsequent fluoridation treatment were used to create superhydrophobic surfaces. After laser processing, nanoporous structures were generated inside the grooves, while the cracked layer was deposited on the non-irradiated area, building up a micro/nanoscale morphology on the ceramic surface. Moreover, the effects of groove pitch and laser scanning cycle on surface morphology and wettability were investigated. Results indicate that the fluoridated groove-like microstructured surface showed good superhydrophobicity based on the Cassie-Baxter model. Dynamic behavior of water droplets impacting on the as-prepared superhydrophobic surface was studied to verify its low adhesion. Additionally, the superhydrophobic surface exhibited remarkable repellency to various stain liquids and outstanding self-cleaning properties. These findings may contribute to developing anti-fouling applications for the architectural ceramics industry.

Dynamic behavior of water droplets impinging on a heated cylinder with various diameter ratios

Dynamic behavior of water droplets impinging on a heated cylinder with various diameter ratios

Anti-freezing characteristics of water droplet impinging the superhydrophobic surface: An experimental and predictive study

Water freezing has a significant and non-negligible influence on the aircraft, power transmission lines and operational efficiency of industrial facilities. Therefore, it is of great value and meaning to deeply understand the dynamic behaviors of water droplet impacting the supercooled superhydrophobic surface. In this work, effects of impact velocity, surface temperature and inclined angle on the impinging droplet dynamics are visually investigated. The machine learning model is first proposed to predict the rebound height and temperature limit of fully rebound. The results demonstrate that a larger impact velocity shifts the temperature limit of completely rebound to a higher surface temperature. However, it has little effect on the spreading time and contact time. As the temperature further decreases, portion of droplet is pinned on the substrate instead of fully rebound and the volume of residual droplet increases. As the inclined angle increases, both contact time and rebound height decreases. Due to driven by the tangential component of gravity, width of droplet before detachment increases while the stretched length decreases. The optimal temperature limit of fully rebound is −35 °C with the inclined angle of 30° and We = 19, showing a significant improvement compared to the temperature limit on a horizontal surface.

Effect of wettability on droplet impact: Spreading and splashing

This study experimentally investigates the dynamic behaviors of water droplets over wide ranges of diameters and velocities (200 μm < D0 < 2600 μm, 50 < We < 3000) impacting on surfaces with various wettability (ranging from hydrophilic to superhydrophobic), and focuses on the effect of surface wettability on water droplet spreading and splashing. The experimental results show that the surface wettability contributes to the lift of the lamella, related to the cosine of the advancing angle (cosθa), that significantly influence the spreading and splashing. The lifting lamella promotes the spreading speed by reducing the surface friction and the viscous dissipation in the boundary layer. The mean spreading speed is linear to the impact velocity on each surface type, and the contact angle slightly affects the mean spreading velocity on the hydrophilic or hydrophobic surface. While, the mean spreading velocity on the superhydrophobic surface is much larger than the other surfaces due to the fewer viscous dissipation. The splashing behavior is dominated by the force from the air surrounding the lamella. The experimental results demonstrate that the splashing threshold K = OhRe1.25 is independent of the advancing angle for the case of θa < 90°, but is proportional to cosθa for the case θa > 90°. Furthermore, we put forward a prediction model of droplet splashing threshold, considering the effect of surface wettability, as K/K0 = 1 + αcosθa, which could quantitatively express the effect of surface wettability on water droplet splashing.

Experimental Study of the Wettability Characteristic of Thermally Treated Shale.

Extraction of shale gas from shale reservoirs is significantly affected by shale wettability. Recently, thermal recovery technologies (e.g., combustion) have been tested for shale gas recovery. This requires an understanding of the wettability change mechanism for thermally treated shale samples. In this study, the effect of combustion on shale wettability was investigated. Shale samples were first processed to obtain smooth surfaces and then combusted at temperatures of 200, 400, and 800 °C. The initial contact angles and dynamic behavior of water droplets on shale surfaces were recorded using the sessile drop method. It was found that pores and fractures were generated on the shale surfaces following high-temperature combustion. The pore volume and diameter increased with increasing combustion temperature, which improved the connectivity of hydrophilic pore networks. Compared to a raw shale sample, the shale sample combusted at 400 °C showed a smaller initial water contact angle and a more rapid decrease in the contact angle because of the oxidation of organic matter and generation of pore structures. Water droplets were found to completely spread over the surface of the shale sample combusted at 800 °C because of the generation of fractures. Moreover, the van der Waals potential between water droplets and combusted shale samples was determined to be stronger. However, the initial contact angle and dynamic behavior of water droplets did not show a significant change for the shale sample combusted at 200 °C. As a result, high-temperature combustion (≥400 °C) can be used to significantly improve the hydrophilicity of shale.

Study on dynamics and freezing behaviors of water droplet on superhydrophobic aluminum surface

In this work, a kind of superhydrophobic aluminum surface (treated-Al-SA) is fabricated by chemical etching using hydrochloric acid and hydrogen peroxide, and then treated by stearic acid. The surface of treated-Al-SA has typical hierarchical structure, which hold its durable superhydrophobicity under water droplet impact test, bending test, temperature test, humidity test and corrosive liquids test. Moreover, treated-Al-SA show excellent self-cleaning property at the different tilt angle under room temperature. Results on the dynamic behavior of water droplet is indicated the good anti-adhesion and superhydrophobicity of the treated-Al-SA. The whole freezing process of the water droplets on the surface of untreated-Al and treated-Al-SA is observed. The freezing time of treated-Al-SA is 59 s, which is longer than that of untreated-Al. It is estimated that the different anti-freezing behavior is caused by the thermal conductivity between the water droplet and plate, which is provided an insight into freezing characteristics of water droplet. This study is offered the novel opinion of the superhydrophobic aluminum surface produced by chemical etching, which may help the application of structured aluminum surface.

Direct Visualization of Microscale Dynamics of Water Droplets on under-Oil-Hydrophilic Membranes by Using Synchrotron White-Beam X-ray Microimaging Techniques.

Despite considerable academical and practical interests on separation of water-in-oil emulsion via special wettable membranes, fundamental understanding on microscale dynamics of water droplets on under-oil-hydrophilic membranes (UOHMs) at early stages during separation is still very preliminary due to temporal and spatial resolution of existing visualization techniques. To this end, we here succeed in a direct microscopic visualization of separation processes of water droplets on the UOHMs by employing a high-speed, two-dimensional synchrotron white-beam X-ray microimaging technique. During the separation of water-in-oil emulsion, microscale dynamic behaviors of water droplets on hydrophilic membrane surfaces immersed in the different oil media (i.e., hexane, kerosene, and light and heavy mineral oils) and oil films between water droplets and membrane surfaces are visualized and analyzed.