Ethanol Droplets Research Articles

Streaming flows within ultrasonic levitators

The streaming flows inside a single-axis ultrasonic levitator are experimentally investigated using particle imaging velocimetry (PIV). Detailed quantification of the flow motion within the levitator is provided for both scenarios, with and without a suspended droplet. In the case of suspended droplets, both water and ethanol are studied to investigate the varying external streaming around droplets with different volatilities. The quantified PIV results reveal two acoustically induced jet flows, originating from the transducer and reflector, within the empty levitator in the absence of a suspended droplet. These flows, identified as Eckart streaming, dominate the external streaming around less-volatile water droplets by directly interacting with their surfaces. For highly volatile ethanol droplets, the Stefan flow, which carries ethanol vapor away from the droplet surface, is clearly observed. This flow counteracts the motion of Eckart streaming within the levitator, preventing it from reaching the surface of the ethanol droplet. This observation confirms the presence of Stefan flow around a highly volatile droplet in the ultrasonic levitator. The interaction between Stefan flow and Eckart streaming determines the external streaming patterns of the ethanol droplet, which significantly differ from those around water droplets. Additionally, boundary-driven acoustic streaming near the droplet surface, also known as Rayleigh–Schlichting streaming, can only develop in the presence of a strong Stefan flow leaving from the highly volatile ethanol droplets. In contrast, without the “protection” of this robust Stefan flow, the boundary-driven streaming around less volatile water droplets are swept away by Eckart streaming within the levitator. This study emphasizes the importance of considering both Eckart streaming and Stefan flow when modeling the transport phenomena of droplets suspended in single-axis ultrasonic levitators. The differences in external streaming patterns between less volatile and highly volatile droplets may influence their corresponding heat and mass transfer processes in the levitator.

Wetting dynamics and heat transfer of droplet evaporation around boiling point: Facile manipulation by surface roughness

The evaporation of water–ethanol droplets on solid surfaces has vast potential for applications in thermal management, microfluidics, and biomedical sciences, while the approach of manipulating wetting dynamics and heat transfer of droplet evaporation around the boiling point remains open for investigations. The present study proposes a facile approach: fabricating solid surfaces with diverse roughness by sandpaper milling with different grit densities, which can alter the wetting and heat transfer characteristics of droplet evaporation. We discover that when the temperature of the heated surface exceeds the droplet boiling point, the existence of bubbles affects the solid–liquid wetting state; surface roughness alters the ability of bubble departure, thus determining the solid–liquid contact and the contact line retraction time. Consequently, in this case, the solid–liquid contact area and the heat absorbed from heated surfaces for droplets changes with surface roughness, altering the droplet evaporation time and the average heat flux at the solid–liquid interface. Bridged by droplet wetting dynamics, the heat transfer of droplet evaporation above the boiling point can be manipulated by adjusting surface roughness, offering a facile approach to tuning the process of droplet evaporation in the related industrial applications.

Electrocombustion Characteristics of Iron Particle-Laden Methanol and Ethanol Droplets in a Direct Current Field

ABSTRACT This study investigates the electrocombustion and atomization behavior of single droplets (2.5 wt.% Fe) of ethanol (EtOH) and methanol (MeOH) fuels at the droplet scale. The experiments utilize a system with two opposing plate electrodes of varying distances (200, 150, and 100 mm) and both negative (↓) and positive (↑) polarizations within a vertical direct current (DC) electric field. The results show that for EtOH and EtOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 100 mm plate spacing, while for MeOH and MeOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 200, 150 and 100 mm plate spacing. Increasing electric field strength reduced the micro-explosion tendency of Fe particles in the flame region and the micro-explosion intensity of Fe particles was found to be higher in ethanol droplets than in methanol. No systematic relationship could be established between the electric field effect and the presence of Fe particles. The MeOH/Fe/150(↑) droplet exhibited the lowest extinction time of 1050 ms. The electric field fundamentally alters the secondary atomization process of the fuel droplets. Notably, the diameter regression of all MeOH-based fuel droplets deviates significantly from a linear relationship. The investigation into the combustion behavior of pure EtOH, MeOH, and their Fe-blended counterparts within an electric field environment suggests that MeOH and MeOH/Fe fuels exhibit superior combustion characteristics. However, further research is necessary to fully elucidate these findings.

Directional Transportation Behavior of Droplets on a Magnetically Responsive Micropillar Array Surface.

Technologies for manipulating droplets have applications in various fields, such as biomedical devices, chemical engineering, water collection, and thermal management. The morphology of magnetically responsive surfaces are modified using magnetic fields for inducing droplet directional rolling and bouncing. Herein, a study on the directional transport of droplets on magnetically responsive surfaces is reported, identifying three movement modes and analyzing the mechanisms influencing the transport behavior. The study explored working fluids with surface tension lower than that of water, achieving the directional transport of 30% ethanol droplets with a maximum transport velocity of 130 mm s-1. The practical applications of the droplets on a modified surface were analyzed, and methods were developed to accelerate droplet mixing. This study explored efficient operations and automation of complex chemical processes.

Study on the acoustic disturbance characteristics of the spray flame

The axial sound field was added to the ethanol spray flame as a perturbation element to study the dynamic response and combustion characteristics. A forced acoustic field is applied to a small oscillating flame. In cases where the frequency of the external sound field matches the eigenfrequency, even small amplitude self-excited flames demonstrate significant instability. As the intensity of the sound field increases, the amplitude of pressure oscillations sharply rises, and the pressure and flame heat release oscillations are in-phase. When the sound field operates at frequencies other than the eigenfrequency, it has an inhibitory effect on the evaporation and combustion process of ethanol droplets. Consequently, intensifying the sound field leads to a reduction in both the area of the evaporation combustion zone and the axial temperature of the flame. The CO formation is influenced by both temperature and the sound field, showing a pattern of increasing and then decreasing with the increase of sound intensity. Additionally, NOx generation exhibits higher emission concentrations in low-temperature and short flames, which is more likely to prompt NOx and is not closely related to frequency.

Critical radius deviated from Leidenfrost state of droplets on liquid layer

The levitation of Leidenfrost droplets on liquid pool is fascinating, but its final stage is lack of understanding. Here, we found that a droplet levitated on liquid layer eventually deviated from Leidenfrost state once its radius was lower than a critical radius due to evaporation. The critical radius of ethanol droplet deviated from Leidenfrost state on silicone oils with a thickness ranging from 2.0 to 15.0 mm was determined by experiment. The influences of the initial radius of droplet, viscosity, and thickness of liquid layer on critical radius were analyzed. In addition, the critical radius decreases with increase in superheat for ΔT lower than 25.0 °C, whereas it does not significantly vary after ΔT exceeding 25.0 °C. The bottom temperature Tb of droplet does not approach to saturation temperature even under a high superheat. The experiment found that Marangoni convection existed inside droplet. Based on a theoretical model considering Marangoni convection, the reason for droplet deviated from Leidenfrost state was explained. These findings are helpful for understanding the final state of Leidenfrost droplet on liquid layer and would provide a potential practical application such as extinction of oil pool fires with liquids.

Insight into Mocha Diffusion Occurring during Ethanol Droplet Spreading on Acrylic Paint.

Mocha diffusion, a significant interfacial phenomenon in pottery painting, remains insufficiently understood in the documented literature regarding its dynamics. This study experimentally investigates Mocha patterns by quantitatively dripping ethanol droplets onto an acrylic paint surface. Results indicate that the spreading radius increases with the ethanol mass fraction, while the fractal period decreases. The fractal dimension of all Mocha patterns approximates 1.4087. Marangoni flow, generated by the volatilization of ethanol, is crucial for the growth and fractal formation of the "dendrites" in this spreading. The scaling analysis is used to interpret the spreading dynamics. This work encourages the interface science community to develop a comprehensive theory for the dynamics of Mocha diffusion and highlights the potential of this intriguing decorative technique.

Soil water repellency and its importance for the climate-smart sustainable management of fen peatland soils in Central Poland

The paper aims to assess potential soil water repellency (SWR) in the surface layers of long-term agricultural fen soils. Furthermore, we attempt to enhance our understanding of the links between selected soil properties (e.g., secondary transformation, total organic carbon (TOC) content) and SWR in differently used (grasslands and arable lands) fen soils in the temperate climate zone. The study was conducted in the Grójec Valley, Central Poland. The soil samples for laboratory analyses were collected in June 2022 from 64 sampling points – 56 grassland and 8 arable sites. We found that secondary soil transformation (mursh forming process) was significantly positively correlated with SWR – determined by MED (molarity of ethanol droplet) and WDPT (water drop penetration time) methods (r = 0.42 and r = 0.40, p < 0.05) only in the organic samples (i.e., mursh). The significant positive correlation between SWR and TOC content (r = 0.73 (MED) and r = 0.74 (WDPT), p < 0.05) indicates that, as well as organic matter depletion, there was a decrease in the water repellency of the studied soils. Our results indicate that study fen sites should be rewetted, and that the implementation of the paludiculture must take place in the near future. At a minimum, further arable cultivation of organic soils should be avoided, as they are the most vulnerable to secondary transformation and exhibit high SWR values. Furthermore, in the case of crop production on post-organic soils, it is recommended that the conservation tillage method is applied to prevent further depletion of soil organic matter content.

Rolling up 2D WSe2 Nanosheets to 1D Anisotropic Nanoscrolls for Polarization-Sensitive Photodetectors.

The intrinsic low-symmetry crystal structures or external geometries of low-dimensional materials are crucial for polarization-sensitive photodetection. However, these inherently anisotropic materials are limited in variety, and their anisotropy is confined to specific crystal directions. Transforming 2D semiconductors, such as WSe2, from isotropic 2D nanosheets into anisotropic 1D nanoscrolls expands their application in polarization photodetection. Despite this considerable potential, research on polarization photodetection based on nanoscrolls remains scarce. Here, the uniform crystalline orientation of WSe2 nanoscrolls is achieved conveniently and efficiently by applying ethanol droplets to vapor deposition-grown bilayer WSe2 nanosheets. Angle-resolved polarized Raman spectroscopy of WSe2 nanoscrolls demonstrates vibrational anisotropy. Photodetectors based on these nanoscrolls show competitive overall performance with a broadband detection range from 405 to 808nm, a competitive on/off ratio of ≈900, a high detectivity of 3.4×108 Jones, and a fast response speed of ≈30ms. Additionally, WSe2 nanoscroll-based photodetectors exhibit strong polarization-sensitive detection with a maximum dichroic ratio of 1.5. More interestingly, due to high photosensitivity, the WSe2 nanoscroll detectors can easily record sequential puppy images. This work reveals the potential of WSe2 nanoscrolls as excellent polarization-sensitive photodetectors and provides new insights into the development of high-performance optoelectronic devices.

Physics Of Two-Stage Evaporation Of Volatile Droplets Suspended In An Ultrasonic Levitator

The evaporation process of mono-component droplets in an ultrasonic levitator is experimentally monitored, focusing on three types of volatile liquids: methanol, ethanol, and 2-propanol. This investigation reveals a ‘two-stage’ evaporation process characterized by an initial rapid evaporation stage followed by a significantly slower evaporation stage; a pattern consistently observed across all three volatile liquids. However, for droplets of comparable size, methanol droplets evaporate faster in the rapid stage than ethanol and iso-propanol droplets and enter the slow evaporation stage earlier. On the other hand, during the slow evaporation stage, 2-propanol droplets exhibit the lowest evaporation rate compared to methanol and ethanol droplets. To explain the two-stage evaporation and the varying evaporation characteristics of mono-component droplets with different volatile components, the streaming patterns within the levitator, with and without a suspended droplet, are visualized and quantified using Particle Imaging Velocimetry (PIV). Two acoustic-induced jet flows, originating from the transducer and reflector of the levitator and considered as Eckart streaming, are observed within the empty levitator. These jet flows move toward the levitated droplet, influencing its evaporation process. Additionally, Stefan flow, carrying vapor away from the surface of the volatile droplet, is clearly observed due to rapid evaporation. The competition between Stefan flow and Eckart streaming ultimately determines the external streaming patterns around the investigated droplets. A theory combining the external streaming patterns and vapor enrichment is proposed to interpret the two-stage evaporation and the corresponding characteristics of the evaporating droplets suspended in the levitator. Furthermore, this study captures boundary-driven acoustic streaming near the droplet surface, known as Rayleigh–Schlichting streaming, whose dimensions and motion vary with the different liquid components and the properties of the corresponding vapor. In summary, the study highlights the presence of Eckart streaming in the ultrasonic levitator and Stefan flow outside an evaporating volatile droplet. Considering these flow patterns is essential for explaining the ‘two-stage’ evaporation and the relevant characteristics within the ultrasonic levitator.

Sonochemical synthesis of hollow mesoporous silica spheres (HMSSs) and its effective utilization for one-step synthesis of curcumin-loaded HMSSs

Herein, HMSSs were successfully synthesized using the sonochemical method. Compared with a conventional synthesis under continuous stirring, HMSSs synthesized under ultrasound irradiation were uniform hollow spheres with a thinner mesoporous shell, resulting in higher pore volumes and larger specific surface areas. The hollow cores were acquired without the templates but from ethanol droplets generated in situ by ultrasound. The ethanol/water volume ratio (E/W) affected the structures of sonochemical synthesized particles, i.e., mesoporous silica particles were obtained at low E/W before transforming to HMSSs under moderate E/W and dense silica spheres at high E/W. Varying [NH4OH] base catalysts in an aqueous phase altered the core structure of HMSSs from hollow cores at high [NH4OH] to partial-filled cores at a moderate concentration and non-hollow cores at low [NH4OH]. Ultrasound was effectively utilized to prepare curcumin-loaded HMSSs in a single step. Stable ethanol droplets containing curcumin were produced from the ultrasound's homogenizing effect, leading to curcumin's encapsulation within HMSSs. While the cavitation induced the chemical effect, reducing the reaction time. The encapsulation of curcumin and the formation of HMSSs could occur concurrently; thus, not only is the drug loading step unnecessary, but the efficiency of loading drugs inside HMSSs is also enhanced.

Study on the electrostatic shedding and crushing characteristics of ethanol and diesel droplets

The study of electrostatic shedding and crushing characteristics of droplets is the basis of understanding electrostatic atomization, and the study of its shedding and crushing behavior in electrostatic field is conducted. Micropump drive is used to control the flow rate, electrostatic generation device to form a stable electric field, light lighting and high-speed camera to obtain the dynamic behavior of shedding and crushing process, and use digital image processing technology to extract the process parameters. The results show that: when the capillary tube diameter and flow are unchanged, when the electric field voltage is low, the droplet deviates and falls off, the diesel droplet is smaller than the ethanol; when the electric field voltage is moderate, the droplet is closed or deformed into wave strip; only when the flow rate increases and the electric field voltage is large, the average particle size of ethanol is smaller than diesel, indicating that the electrostatic atomization effect of ethanol with small surface tension is significantly better than that of diesel oil.

Phase-sensitive optical coherence tomography reveals droplet penetration into a powder bed

Understanding the mixing behavior that unfolds when liquid droplets impact on powder beds requires a sub-surface dynamic imaging method that provides high spatial and temporal resolution. In this study, a high-resolution phase-sensitive optical coherence tomography (PhS-OCT) technique was introduced to provide in-depth insights into the interaction of droplets and powder beds. A theoretical model correlating changes in the optical path differences (OPD) of the OCT signal with physical properties of the powder bed was presented. Experiments were conducted on three powders with median particle diameters, i.e., the size corresponding to the 50th percentile of the cumulative volume distribution, of 3 µm (mannitol), 4 µm (mannitol) and 109 µm (SV010). Water and ethanol droplets were used to illustrate the technique. The results demonstrated that OPD maps can qualitatively resolve the liquid-powder mixture region, both temporally and spatially, as the droplet diffuses into the powder bed, allowing for a quantitative description of diffusion behavior. A comparison of lactose and mannitol powder samples revealed varying diffusion rates, potentially attributed to differences in porosity, particle size, and agglomeration. Additionally, water and ethanol droplets exhibited significantly different (p = 0.005) diffusion profiles for the same powder properties. In general, the findings indicate the potential of the proposed PhS-OCT technique for evaluating the mixing behavior of multi-phase mixtures, holding promise in applications such as pharmaceutical drug formulations and additive manufacturing.

Effect of flame characteristics on an isolated ethanol droplet evaporating through stagnation methane/air flames: An experimental and numerical study

A single ethanol droplet evaporation through laminar methane/air stagnation flame is investigated at lean, stoichiometric and rich conditions experimentally and numerically. For the droplets having initial diameters of 20-70μm, the particle Reynolds number is measured via PIV/PTV, resulting in the slip velocity between the droplet and gas flow being small and the surrounding gas being able to carry without any significant convective effects. Evaporation rates, computed from Abramzon–Sirignano for a moving droplet towards a stagnation flame field, satisfy the ones computed from empirically determined evaporation rates from ILIDS measurements as a function of flame temperature, flame speed and flame thickness. Nevertheless, Abramzon–Sirignano model slightly overestimates the vaporization constant for lean cases. The distance traveled by the droplet after leaving the flame zone determines the average critical diameter. Accordingly, droplets larger than 18μm can cross the flame, leading to local modifications in the flame region due to heat loss and vapor diffusion from the droplet. Novelty and Significance Energy conversion in combustion should be carried out by optimizing efficiency, minimizing pollution, and preventing further climate change. The multiphase nature of spray combustion particularly adds further complexity due to the strong coupling of atomization, evaporation, mixing, turbulence, and chemical reactions. Although spray combustion involves a cloud of polydispersed droplets, it is of fundamental importance to understand the dynamics of an isolated droplet and its interactions with the flame front, which can provide indispensable information for spray combustion models. In this study, an experimental and computational framework has been developed to investigate droplet-flame interactions. The dynamics and evaporation characteristics of an isolated droplets interacting with stagnation flames have been determined by coupling several laser diagnostics, while further enhanced with Eulerian–Lagrangian simulations under flame conditions. Thereupon, the outcomes help the design of injectors of spray combustion systems and enhancement of evaporation models.

Soil water repellency along elevation gradients: The role of climate, land use and soil chemistry

The rate of water infiltration, surface runoff, and overland flow are all affected by soil water repellency (SWR), i.e., the reduced affinity for water caused by hydrophobic coatings on soil particles. SWR impacts water balance, which in turn affects ecosystem’s function and watersheds hydrology, but little is known about changes of these properties along elevation gradient. Here, we investigate variation in SWR along four elevation gradients in four Italian mountain peaks, encompassing different land use and vegetation types from Mediterranean to temperate and alpine ecosystems. A total of 240 soil samples were collected for 48 ecosystems, and SWR was determined using the molarity of an ethanol droplet test. Soil characteristics were assessed using texture, pH, organic matter content, and soil salinity. Climate data were obtained using WorldClim, and their relationship with SWR was examined. SWR showed a unimodal pattern along the four elevation levels and in all cases peaked at mid-elevations between 1000 and 2500 m a.s.l.. SWR was highest under coniferous and deciduous forests and lowest for arable and bare soil. Soil organic matter and pH were the main determinants of SWR, with a positive and negative correlation, respectively. As for climate, mean annual temperature showed a hump-shaped relationship with SWR. In detail, we found that soil was hydrophilic at the extremes of elevation gradient where mean annual temperatures are less than −3.4 °C for alpine bare soils and higher than 12.7 °C for arable soils. This study allowed us to show how land use, soil chemistry, and climate are related to SWR along an elevation gradient. Further research is needed to concretely evaluate the effect of SWR on erosion risk at the watershed scale in the context of climate change.

Impact of Heat on Soil Water Repellency in Forest Soils from Different Depths using Water-Repellent Japanese Cedar (Cryptomeria japonica) Forest Soil

ome soils under plant species, such as casuarina, pine, eucalyptus, cedar, and cypress, show water- repellent conditions. Wildfires are common in forests dominated by these plant species as they produce highly flammable debris. The heat generated during wildfires alters soil characteristics, including soil water repellency (SWR). The responses of SWR to heat can differ depending on the heating temperature and the soil depth. This study aimed to examine the effects of different heating temperatures on SWR through a soil profile using Japanese cedar (Cryptomeria japonica) forest soil in Japan. Soil samples were collected from four different depths (0-5, 5-10, 10-15, 15-20 cm). Soils were exposed to heat with seven heating temperatures (TH) (50, 100, 150, 200, 250, 300, and 350° C) separately for 1 h using a programmable muffle furnace. The degree (contact angle) and the persistence of SWR in both heated and non-heated samples were measured using the molarity of an ethanol droplet test and the water drop penetration time (WDPT) test, respectively. In non-heated soils, the 0-5 cm layer showed the highest SWR (contact angle ~110°; WDPT≥3600 s). SWR decreased with depth to be non-repellent at 15-20 cm (contact angle≤90°; WDPT≤1 s). In heated samples, SWR of 0-5, 5-10, and 10-15 cm layers decreased with increasing TH, while the selection from 15-20 cm was non-repellent in all treatments. Soils of 0-5 cm depth showed extreme SWR (WDPT=≥3600 s) up to 200° C and became non-repellant at 250° C, while those of 5-10 cm showed extreme SWR up to 150° C, severe SWR (WDPT~1350 s) at 200° C, and became non- repellent at 250° C. The soils from 10-15 cm showed severe SWR (WDPT~2100 s) at TH of 50° C and became non-repellent at 100° C. Results revealed that upper soil layers with higher SWR required higher TH to become non-repellent, and soils from lower layers with lower SWR became non-repellent at lower TH. Further experiments are necessary to identify the changes in molecular levels of organic matter in response to the impacts of heat on SWR. &#x0D; Keywords: Cryptomeria japonica, Laboratory heating, Soil water repellency, Wildfires

Toward Advanced Superomniphobicity: Hierarchical Insights from Serif-T Nanostructures to Microscale Wrinkles.

Developing a superomniphobic surface that exceeds the static and dynamic repellency observed in nature's springtails for various liquids presents a significant challenge in the realm of surface and interface science. However, progress in this field has been particularly limited when dealing with low-surface-tension liquids. This is because dynamic repellency values are typically at least 2 orders of magnitude lower than those observed with water droplets. Our study introduces an innovative hierarchical topography demonstrating exceptional dynamic repellency to low-surface-tension liquids. Inspired by the structural advantages found in springtails, we achieve a static contact angle of >160° and the complete rebound of droplet impact with a Weber number (We) of ∼104 using ethanol. These results surpass all existing benchmarks that have been reported thus far, including those of natural surfaces. The key insight from our research is the vital role of the microscale air pocket size, governed by wrinkle wavelength, in both static and dynamic repellency. Additionally, nanoscale air pockets within serif-T nanostructures prove to be essential for achieving omniphobicity. Our investigations into the wetting dynamics of ethanol droplets further reveal aspects such as the reduction in contact time and the occurrence of a fragmentation phenomenon beyond We ∼ 350, which has not been previously observed.

A dual-height wick to improve capillary performance of vapor chambers

The wick performance is a crucial metric for ensuring the reliable and efficient operation of vapor chambers (VCs) away from dry-out. To enhance the performance of VC, a pitcher plant inspired enhanced wick characteristic dual-height microgrooves (DHMW) was fabricated on 6063 aluminum alloy by one-step picosecond laser texturing without chemical modification. This study describes the two-step capillary behavior of DHMW by high-speed camera and infrared camera. The effects of minor rib number, groove height ratio, length scale, and test liquids (water, acetone, ethanol) on the capillary performance were investigated. When using water as the working fluid, the DHMW achieved a K/Reff of 1.182 µm, which was about 71.3 % larger than that of normal microgroove wicks due to the liquid propagation effect and the flow resistance reduction effect. Furthermore, the maximum K/Reff could reach 1.819 µm of the sample with a minor rib depth of about 70 μm. However, the wetting results showed that the droplets of acetone and ethanol tend to spread laterally after contact with the surface, which is unfavorable for the formation of hierarchical transport in the DHMW. This study demonstrates that laser texturing is an effective and controllable method for the complex shaping of grooved aluminum wicks, with the potential to improve the heat transport capability of VCs.

Spreading of volatile droplets in a humidity-controlled environment.

When a pure ethanol droplet is deposited on a dry, wettable and conductive substrate, it is expected to spread into a thin, uniform film. Here, we demonstrate that this uniform spreading behaviour can be altered significantly by controlling the ambient relative humidity. We show that higher relative humidity not only promotes faster spreading of the droplet, it also destabilizes the moving contact line, resulting in a fingering instability. We observe that these effects primarily emerge due to the hygroscopic nature of the pure droplet, which eventually leads to solutal-Marangoni effects. Additionally, heat transfer between the evaporating droplet and the underlying substrate also plays a crucial role in the overall dynamics. Thus, the overall spreading of a pure hygroscopic droplet is determined by a delicate interplay between solutal and thermal Marangoni effects.

Drying microcharacteristics of volatile and non-volatile droplets on smooth and structured surfaces

In order to analyze the dynamics of droplet evaporation from solid surfaces and to study the liquid-solid interactions, liquid droplets were deposited on substrates and examined under a microscope. Due to the variation of interfacial tensions at liquid-gas and at liquid-solid the contact line changes depending on the type of solid surface and liquid. In this study, two liquids with different surface tensions (water and ethanol) are employed to examine the effects of evaporation time and to elucidate the underlying mechanisms of solid-liquid interactions. In the case of rapidly evaporating ethanol droplets, the formation of residual droplets and internal currents was observed. In contrast, the evaporation of water droplets resulted in only a change in the shape of the contact line. The paper presents a dependence of the Ohnesorge number on the dimensionless diameter, which characterizes all the considered types of interaction. Additionally, an analysis of the contact angle and contact diameter is presented.