Droplet Spreading Research Articles

Impingement of a water droplet onto a rotational surface

In the present study, the impact of a water droplet onto a rotational surface was experimentally studied. The effects of the impact velocity, the rotational speed, and the impact radial position on the impact phenomena were carefully investigated. The phenomena of asymmetric spreading, finger formation, and secondary droplets were observed. Moreover, experiments of a water droplet impacting onto a stationary surface with different impact velocities were also conducted for comparisons. The results showed that, at the same impact velocity, the increase in the rotational speed or the impact radial position could result in the increase in the wetting length in the angular direction and the wetting area. In addition, at the same impact velocity, the dimensionless wetting length in the radial direction on the rotational surface was generally lower than the spreading factor on the stationary surface. In addition, new correlations for the spreading ratio, the dimensionless excess spread area, the dimensionless maximum wetting area, and the number of fingers appearing at the angle of 50° after impact were proposed. The increase in the impact velocity and the surface linear velocity could both promote the formation of the fingers at the angle of 50° after impact. In addition, the dimensionless horizontal displacement of the secondary droplet was found to be mainly influenced by the impact velocity, while the surface linear velocity only had a minor influence.

Molecular dynamics simulation of nanodroplet impacting on high-temperature plate wall

The process of droplet impacting on a high-temperature wall is widely existent in daily life and industrial applications. Most of scholars mainly have focused on experimental and macroscopic research on this phenomenon. In this work, molecular dynamics simulation is conducted to investigate the evolution of droplet and the influence of surface temperature on its evolution, in order to explore the heat transfer mechanism of nanodroplet impacting on high-temperature surface. Droplet containing 10741 argon atoms impacts on the copper plates at temperatures of 85, 150, 200, 250 and 300 K, respectively. The number of droplet evaporation atoms is statistically obtained, the droplet barycenter displacement is analyzed, and the density distribution and temperature distribution inside the droplet are acquired. It is shown that the droplet exhibits different characteristics on the wall at different temperatures. The droplet finally stabilizes on the wall at 85 K as shown in Fig. (a), but when the temperature of the wall rises to 150 K, the droplet evaporates slowly and finally completely as shown in Fig. (b), and for the wall temperatures 200, 250 and 300 K, the Leidenfrost phenomenon is found: the droplet is suspended above the wall as displayed in Figs. (c)–(e). Fig. (f) shows the number of evaporated atoms at different wall temperatures. It also can be seen that the Leidenfrost phenomenon occurs at wall temperatures 200, 250 and 300 K, because for the three conditions there are rise steps and then the numbers of evaporated atoms almost keep constant. For the temperature conditions under which the Leidenfrost phenomenon can occur, the higher the wall temperature, the faster the droplet evaporates, the earlier the detachment occurs from the wall, the greater the droplet detaching velocity, and the larger the final suspending droplet volume. The analyses of the density distribution and temperature distribution of the droplet at the moment when it detaches from the wall show that the evaporation process is faster and a thicker vapor layer is generated due to the higher heat flux of the high-temperature wall, which will hinder the heat exchange, so that the average temperature of the droplet is lower and the average density is smaller.

Study on Marangoni explosion of binary mixtures in liquid layer

In this work, the process of forming micro-droplets due to instability and fragmentation after short chain alcohol solution spreads on the surface of oil layers is studied. Based on the free energy theory of the liquid-liquid interface, the relationship between the binary mixtures spreading on the surface of the liquid layer is derived, and the concentration range of short chain alcohol solution spreading as a thin film on the surface of the oil layer is calculated from the Hiskovsky formula. The Malangoni flow caused by the difference in evaporation rate between the center and edge of the droplet film perturbs the boundary of the liquid film, causing finger-shaped liquid columns to grow at the edge when the droplet spreads to its maximum. In this work, the expression for the critical wavelength and maximum wavelength of boundary instability are derived based on the perturbation model, and the reason for finger shaped liquid column fragmentation is explained based on the Plateau Rayleigh instability. A concentric cylindrical shell liquid column model is established to simplify the calculation and predict the location range of “droplet explosion” of droplets with different viscosity ratios on the liquid layer. Through theoretical calculations and experimental verification, it is found that the alcohol solution fragmented into small droplets within a length range of 4.51–5.98 times the width of the liquid column. This study provides theoretical guidance for existing application fields such as film forming technology and coating technology. The hypotheses, assumptions, and simplified models preliminarily verified experimentally provide solutions for some technical difficulties in the research fields of micro reactions and nanoparticle preparation in chemical industry.

ANALYSIS OF THE DYNAMICS AND FREEZING OF WATER DROPLETS ON METAL SURFACES

This article investigates the effects of substrate temperature, tilt angle, and droplet size on droplet impact dynamics and freezing using a Motionpro high-speed camera and a DSA-30 droplet surface analyzer. The temperature of the substrate was changed from the ambient temperature of 21°C to -13°C, and three droplet sizes (<i>D</i><sub>0</sub> = 2.57, 3.02, and 3.54 mm) were studied. The results show that some air gets trapped under the liquid film during the impact process due to insufficient escape time, resulting in the interior of the droplet being in an unstable state. Simultaneously, due to the low surface energy of the substrate, liquid droplets exhibit a rebound effect upon impact with the ambient temperature substrate, reaching their maximum height and forming a dumbbell-like shape. Furthermore, the rebound height decreases rapidly with the decrease in substrate temperature. A change in substrate temperature had no significant effect on the droplet spreading process, but decreasing substrate temperature increased the viscous forces, thereby suppressing the droplet retraction and oscillation processes, ultimately leading to longer droplet freezing times. Additionally, at low Weber numbers (<i>We </i>< 250), the droplet dimensionless parameters exhibited a similar trend with respect to dimensionless time or temperature.

A ternary mixture model with dynamic boundary conditions.

The influence of short-range interactions between a multi-phase, multi-component mixture and a solid wall in confined geometries is crucial in life sciences and engineering. In this work, we extend the Cahn-Hilliard model with dynamic boundary conditions from a binary to a ternary mixture, employing the Onsager principle, which accounts for the cross-coupling between forces and fluxes in both the bulk and surface. Moreover, we have developed a linear, second-order and unconditionally energy-stable numerical scheme for solving the governing equations by utilizing the invariant energy quadratization method. This efficient solver allows us to explore the impacts of wall-mixture interactions and dynamic boundary conditions on phenomena like spontaneous phase separation, coarsening processes and the wettability of droplets on surfaces. We observe that wall-mixture interactions influence not only surface phenomena, such as droplet contact angles, but also patterns deep within the bulk. Additionally, the relaxation rates control the droplet spreading on surfaces. Furthermore, the cross-coupling relaxation rates in the bulk significantly affect coarsening patterns. Our work establishes a comprehensive framework for studying multi-component mixtures in confined geometries.

The role of poroelastic diffusion in the transient wetting behavior of hydrogels.

Wetting and water absorption of hydrogels is often encountered in many applications. We seek to understand how wetting behavior can be affected by the time-dependent swelling of hydrogels. We measured the advancing contact angles of water droplets on hydrogels of varying thicknesses where thicker gels absorbed water more slowly. We also observed that, above a threshold advancing speed, water droplets would collapse into a lower contact angle state on the surface. We hypothesized that this collapse threshold speed is a result of competition between the poroelastic diffusion of water into the gel and the advance of the spreading droplet, the thickness of the surface, and the diffusion of water into the gel. Taking the ratio of the diffusion and advancing timescales results in a Peclet number with gel thickness as a characteristic length scale. Our results show that above a Peclet number of around 40, droplets will collapse on the surface across all gel thicknesses, confirming our hypothesis. This work provides simple insight to understand a complex time-dependent wetting phenomenon for a widely used hydrogel.

Behavior of a sessile droplet over dielectric infused hydrophobic surface under direct current electric field

The manipulation of sessile droplets on hydrophobic surfaces with high controllability, accuracy, and flexibility is vital for various applications of engineering sciences and technology. In this research, the combined effects of a uniform electric field, dielectric infused surface (DIS), and surfactants were investigated for the manipulation and control of sessile droplets on hydrophobic substrates. DIS reduced surface adhesion and enabled the action of electrohydrodynamic and electrophoretic forces. Experimental analysis revealed three different modes of droplet behavior on DIS under varying electro-physical conditions: elongation without motion, elongation with motion, or dispersion. These modes were observed for surfactant concentrations below the critical micelle concentration (CCMC), while elongation leading to restricted spreading of droplet occurred above CCMC. The modes were mapped in the parametric space of electric capillary number (Cae) vs. non-dimensional surfactant concentration (C* = Cs /CCMC), with Cae representing the ratio of interfacial electric to capillary stresses and Cs representing the surfactant concentration. A simple theoretical analysis based on interfacial electric and capillary stress balance distinguished between the stable and unstable configurations. This research contributes to advancing the understanding of droplet manipulation and control, which are critical in emerging microfluidic or biological applications.

Effects of frosting on the impacting droplets spreading and freezing on subcooled surfaces

Droplet impingement on subcooled surfaces has a significant effect on the power industry as well as on the anti-icing process of the wing. Surface temperature, impact velocity, and surface frost are important factors that affect the behavior of droplets on subcooled surfaces. In this paper, droplet dynamic behaviors were analysed for spreading and freezing, and a range of temperatures (Ts = 22 °C ∼ -30 °C) and velocities (U = 0.09 m/s ∼ 0.85 m/s) were tested on the engineering stainless steel hydrophobic surface, with particular regard to the icephobic properties of the frost-free and frosting conditions. It was observed that the surface frosting caused by environmental humidity has a significant influence on the motion of the three-phase contact line and the icephobic properties of the surfaces. The increasing droplet impact velocity results in a higher kinetic energy of droplet spreading upon impingement, which is arrested by the common effects of surface supercooling and frosting, leading to a reduction in the icephobic properties of the eventual frosting surface. Additionally, singular satellite droplets were observed on the frosting surfaces in the case of Ts = -30 °C because frosting provides a roughness that allows for the formation of pockets in which the initial droplet can be trapped. Furthermore, a frost-free surface maintains its original icephobic characteristics in terms of freezing inhibition. For frosted surfaces, freezing height and time decrease with increasing velocity. Finally, when comparing the freezing process of frost-free and frost-covered surfaces, we found that the freezing of frost-free surfaces was faster at low impact velocities, conversely, the freezing of frosted surfaces was faster. Our study provides a valuable guide for future applications of hydrophobic surfaces of engineered metals in practical environments.

Droplet jumping by modulated electrowetting

We investigate jumping of sessile droplets from a solid surface in ambient oil using modulated electrowetting actuation. We focus on the case in which the electrowetting effect is activated to cause droplet spreading and then deactivated exactly at the moment the droplet reaches its maximum deformation. By systematically varying the control parameters such as the droplet radius, liquid viscosity and applied voltage, we provide detailed characterisation of the resulting behaviours including a comprehensive phase diagram separating detachment from non-detachment behaviours, as well as how the detach velocity and detach time, i.e. duration leading to detachment, depend on the control parameters. We then construct a theoretical model predicting the detachment condition using energy conservation principles. We finally validate our theoretical analysis by experimental data obtained in the explored ranges of the control parameters.

Coupled Dynamics of Droplet Impact on a Flexible, Hydrophilic Cantilever Beam.

We experimentally study the droplet impact on a flexible, hydrophilic cantilever beam. Droplets of water, water-glycerol (1:1 v/v), and glycerol were considered on a copper beam. Side visualization of the droplet impact on the cantilever was carried out by using a high-speed camera. We systematically vary cantilever stiffness to obtain a characteristic time scale of the beam dynamics, that is, shorter on the same order and longer than the characteristic time scale of droplet dynamics. Water droplet spreading reduces with an increase in the beam's flexibility, due to the "springboard effect". Results reveal that a threshold cantilever length exists beyond which the droplet vibration mode "locks-in" to the cantilever vibration mode. During lock-in, the bending energy of the beam increases with an increasing length or decreasing stiffness. The time-varying cantilever deflection exhibits an oscillatory, exponentially decaying response. However, in the case where both time scales are almost the same, we found a two-stage damping in the measurements: a fast, initial damping followed by a slower, damped response. We explain this damped response by the interplay of droplet and cantilever early dynamics. As expected, increasing the droplet viscosity dampens the magnitude of droplet spreading and displacement of the cantilever's tip due to a larger dissipation of kinetic energy in the bulk of the droplet. The decay is exponential in all cases, and the time taken to reduce the spreading and displacement is shorter with a larger viscosity. The damping coefficient is found to inversely scale with the cantilever length or mass. We corroborated the measurements with available analytical models, confirming the hypotheses used to explain the results. Overall, the present study provides fundamental insights into controlling the coupled dynamics of droplet and flexible substrates, with potential applications such as the design of efficient agricultural sprays and wings of microaerial vehicles.

Heat transfer process in the collision of high-temperature aluminum droplets with an inclined wall

The heat transfer process occurring when high-temperature aluminum droplets collide with a solid surface is investigated via numerical simulation and experimentation. The wall temperature at the impact point rapidly increases, with some oscillations, reaching a maximum value of 1054.5 K. The maximum wall heat flux density during the droplet–wall collision is 63,135 kW/m2. As the droplet spreads on the wall, the temperature at the impact point undergoes a two-stage decrease: a rapid decrease followed by a slow decrease. During the initial stage of the droplet–wall collision, the wall temperature is asymmetrically distributed, with the increase in temperature at the advancing edge spreading more slowly than that at the receding edge. Similarly, the corresponding heat flux density distribution at that time is also asymmetrically distributed, with higher heat flux density at the trailing edge of the spread than at the leading edge.

Study on the mechanism of surfactant droplet wetting and coagulation of respiratory dust: The case of AEO-9

In industrial production, spraying is the most widely used dust control method. However, the traditional pure water spray has poor dust removal effect, and the principles of droplet wetting and dust encapsulation are unclear, resulting in poor dust removal effect. In this study, based on the CLSVOF method, we investigated the dynamic wetting and coalescence process of surfactant droplets and dust particles from a microscopic perspective. By changing the size ratio between the droplets and dust particles, as well as the initial velocity of the droplets, we simulated the spreading and wetting of surfactant droplets on the dust surface and found the optimal parameter range for encapsulating respirable dust. Through the experimental determination of spray atomization characteristics, it was found that the spray pressure of 6 MPa and the use of a 1.2 mm fine atomization nozzle produced a spray field with droplet sizes ranging from 14 to 21 μm, accounting for approximately 62.4 % of the distribution. Around 60 % of the droplets had velocities between 20 and 30 m/s. Dust settling efficiency experiments were conducted under these optimal spray parameters, and the settling efficiency of respirable dust reached 84.33 % within the favorable parameter range. Numerical simulations of the dynamic wetting process of dust-fog coupling at the microscopic level, as well as macroscopic spray experiments, were carried out to validate the reliable results. This method has significant implications for the control of respirable dust.

Predicting Impact Outcomes and Maximum Spreading of Drop Impact on Heated Nanostructures Using Machine Learning.

Accurate prediction of droplet behavior upon impact on a heated nanostructured surface is vital for various industrial applications. In this study, we leverage multiple data-driven machine learning (ML) techniques to model the impact outcome and droplet spreading, employing existing experimental data. Our approach incorporates a comprehensive range of critical control parameters, such as the impact velocity (V), surface temperature (Ts), nanopillars' packing fraction (ϕ), and surface roughness (r). We obtain optimal results when utilizing the artificial neural network classification (ANNC) to construct a phase diagram that encompasses all of the experimental impact behaviors. Additionally, we utilize the support vector regression (SVR) method to model the maximum spreading factor (βmax) as a function of the Weber number (We), defined as the ratio of droplet kinetic to surface energy, and Ts for each surface combination. Consistent with previous experimental observations, our results illustrate that nanostructures not only introduce distinct impact behaviors, such as central jetting, but also influence the boundaries among the deposition, rebound, and splashing regimes within the phase diagram. An increase in ϕ at a constant r promotes deposition and spreading events, while increasing r at a constant ϕ results in enhanced heat transfer to promote the Leidenfrost effect for the rebound regime and a greater disturbance of the liquid lamella to trigger splashing. The SVR prediction reveals the existence of a We-number threshold governed by the nanostructure parameters. Beyond this threshold, the maximum spreading factor (βmax) of a spreading droplet becomes independent of the surface temperature (Ts) as We increases, suggesting that fluid properties are likely the dominating factors influencing the spreading dynamics in the extreme We range.

Interaction between droplet impact and surface roughness considering the effect of vibration

Droplet impingement is pivotal in several fields, such as agricultural spraying, ink printing and firefighting. Although droplet impact studies have received much attention, the combined effects of roughness and vibration on droplet dynamics still need to be explored. In this study, an in-depth analysis is carried out to address this issue, and high-speed photography is utilised to explore the droplet impact process under different roughness and vibration conditions. The results show that higher surface roughness dissipates the kinetic energy of droplet spreading, thus inhibiting droplet spreading. Conversely, vibration imparts additional inertial effects to the droplet, leading to sustained oscillations once the droplet stabilises, which in turn results in a more pronounced variation in the droplet's dynamic contact angle. Therefore, in this paper, the vibrational Weber number (Wev) is employed to characterise the interaction between the vibration-induced extra inertia force and the droplet's surface tension. Moreover, as the Wev increases, the relative velocity of the droplet impact also rises, further intensifying the droplet's spreading behaviour. At a Wev of 8.72 and a surface roughness of 0.4 μm, droplet spreading is enhanced by 33%. While at a surface roughness of 6.3 μm, droplet spreading was suppressed by 32% relative to a surface roughness of 0.4 μm. Ultimately, an empirical model was proposed to predict the droplets' maximum dimensionless spreading coefficient (βmax) under vibration conditions, with an error of ±9.5% in the model prediction. This study delves into the dynamic characteristics of droplets under the combined influence of surface roughness and vibration, offering crucial theoretical foundations and profound insights for engineering applications in the field.

Three-dimensional lattice Boltzmann simulations for droplet impact and freezing on ultra-cold superhydrophobic surfaces

Droplet impact and freezing on cold surfaces is a widely encountered multi-physical phenomenon involving droplet deformation and the liquid–solid phase change. Due to its complexity in nature, it is challenging to simulate the three-dimensional (3D) droplet impact and freezing process. Furthermore, due to the limitation of experimental techniques, it is not easy to experimentally investigate the impact of liquid droplets on ultra-cold superhydrophobic surfaces, which is crucial in some applications. Thus, in the present work, a 3D lattice Boltzmann (LB) method is developed to simulate the droplet impact and freezing on an ultra-cold superhydrophobic surface, in which an enhanced cascaded LB method is used to solve the multiphase flow field, and a multi-relaxation-time scheme is applied to solve the liquid–solid phase change model. The previous experimental results are numerically reproduced, proving that the present model can satisfactorily describe the droplet impact and solidification. The surface temperatures have no significant influence on droplet spreading. However, during the droplet retraction, a rim of ice first appears near the three-phase contact line, and then, the droplet bottom will completely solidify into ice. The occurrence of solidification at the bottom of the droplet will lead the droplet to break at a lower impact velocity, which can only be observed at a high Weber number on the room-temperature superhydrophobic surface. In addition, the effects of surface temperatures and Weber numbers on the evolution of spreading factors and space-averaged heat flux are also quantitatively analyzed in detail.

High frame-rate imaging of the shape oscillations and spreading dynamics of picolitre droplets impacting on a surface

The post-impact dynamics and spreading rates of picolitre liquid droplets on surfaces are critical to many practical and industrial applications, as well as respiratory disease transmission mechanisms. Here we use a high framerate imaging method to explore the shape oscillations and spreading of individual ∼10–180 pl volume droplets (corresponding to ∼30–70 μm in initial droplet diameter) impacting on a surface under ambient conditions with 10 μs temporal resolution. The method allows the surface tension to be accurately extracted from the measured frequency of post-impact shape oscillations for sessile droplets in this size range with surface tensions greater than 40 mN m−1 and viscosities up to at least 3.2 mPa s. The Tanner's law model for predicting sessile droplet spreading rates provides an accurate account of the “steady-state” spreading rate for all droplets with surface tensions in the range 22–73 mN m−1 studied here. However, Tanner's law does not account for the delay in the onset of spreading observed for droplets in this size range, caused by competition between shape oscillations and spreading governing the morphology at short time periods, particularly for surface tensions >22 mN m−1.

Correlation Between Radiographer’s Level Of Knowledge About COVID-19 With Its Preventive Behavior In Dental Radiography Examination, 2022

Backgroundnd: Health Care Associated Infections (HAIs) including COVID-19 are an ongoing challenge to the safety of patients and health workers as well as the quality of health services that require attention and ongoing efforts to prevent the risk of transmission. Radiographers who perform dental radiographic examinations are at high risk of spreading COVID-19 because of the examination requires close contact with patients and the risk of spreading droplets or aerosols. This research was conducted with the aim of studying and analyzing the relationship between the radiographer’s level of knowledge about COVID-19 and the preventive behavior of its transmission in dental radiographic examinations. Methods: The research was conducted by collecting data using an online questionnaire via Google Forms that distributed to 99 radiographers in East Java. Data analysis was carried out using Spearman’s Rank Correlation to find out the correlation between radiographers’ level of knowledge about COVID-19 and preventive behavior towards its transmission in dental radiographic examinations. Results: Radiographers’ level of knowledge about COVID-19 showed 54% good, 42% moderate, and 4% less. Radiographers’ preventive behavior towards the transmission of COVID-19 in dental radiology installations showed 67% good, 30% moderate, and 3% less. Spearman’s Rank Correlation showed weak correlation between the level of knowledge and preventive behavior with the value of sig. (2-tailed) was 0,032 and correlation coefficient was 0,215(+). Conclusions: The level of knowledge of radiographers in East Java about COVID-19 has significant correlation with the preventive behavior of its transmission in dental radiographic examinations with a very weak strength and unidirectional correlation.

Free surface tension modelling using particle-grid hybrid method without considering gas particles

In particle method, the number of particles is an important factor affecting the computational efficiency. For the free-surface flow, gas particles are usually necessary for surface tension calculation, but they have little impact to the liquid flow with a large density. If the free surface tension can be modeled without considering gas particles, it is of great significance to improve the computational efficiency. The existing potential-based surface tension model and the stress-based surface tension model don't need gas particles, but they have the problems of instability or are difficult to implement. Therefore, in this study, another free surface tension calculation method by coupling particles and grids is proposed. In the method, background mesh is applied to the entire computational domain, where the boundary of grid is extended outward by 3.1 l0 on the basis of particle boundary for curvature calculation. The level-set function is adopted to mark different phases on background mesh, whose value is set according to the normal distance between the grid and the nearest free surface particle. After obtaining the curvature and the level-set function gradient on background mesh, these variables are interpolated to corresponding particles to calculate the surface tension. Through the comparative study of area-weighted and distance-weighted interpolation schemes, it is found that the accuracy of distance-weighted interpolation scheme is higher than that of area-weighted interpolation scheme. Finally, the performance of the particle-grid hybrid method is verified by simulating four benchmark cases, including droplet oscillations, droplet spreading, capillary jet breakup and droplet impinging onto plate.

The effect of vibration on droplet dynamics and heat transfer of spray cooling

The heat transfer mechanism of spray cooling under vibration has yet to be revealed, so it is crucial to deeply analyze the droplet impingement dynamics and heat transfer mechanism under vibration. However, there is still a gap in analyzing how vibration quantitatively affects droplet impingement dynamics and heat transfer performance. To fill this research gap, this paper will employ high-speed cameras to quantitatively analyze droplets' dynamics and heat transfer properties under various vibrational conditions. The results demonstrate that droplet spreading is enhanced at high-frequency conditions, but the enhancement decreases with the reduction in amplitude. Under high amplitude conditions, droplets gain additional inertial forces to overcome adhesive forces, causing oscillation in the three-phase contact line of the droplets, which significantly consumes the kinetic energy of droplet spreading, thereby suppressing droplet spreading. Vibration overall suppresses droplet spreading; at an amplitude of 0.2 mm and frequency of 80 Hz, the spreading enhancement factor is merely 4 %. Moreover, the droplet's heat transfer rate, heat flux, heat transfer coefficient, and cooling efficiency all increase with the rise in vibrational frequency but are all subdued by the amplitude. Compared to a static surface, vibration suppresses droplet heat transfer but can facilitate droplet heat transfer under low amplitude and high-frequency conditions. At an amplitude of 0.2 mm, the maximum heat transfer enhancement factor (HTEF) is 16 %. At an amplitude of 0.8 mm and frequency of 10 Hz, the minimum HTEF is −44 %. This research undoubtedly brings innovative insights into spray droplet impact dynamics and heat transfer and can provide valuable guidance for related industrial applications.

A theoretical model to determine solid surface tension through droplet on film configuration and experimental verification

Determination of the surface tension of solids has been a challenging issue. This work presents an approach to the issue based on the configuration of a droplet spreading on a free standing film. Firstly, a theoretical model for the equilibrium configuration of a droplet spreading on a film is developed, which reveals that the surface elasticity has little contribution to the equilibrium configuration, and the effective strain of the film is determined by the bulge angle analytically. Based on these observations, a new procedure is presented to measure the surface tension of the film through droplet loading, which is realized by extrapolating the film tension as a function of the product of the film thickness and the effective strain. Finally, as a validation, we use this approach to extract the surface tension of soft elastomers. This work provides a viable and robust approach to determination of the surface tension of solids.