Augmented Young-Laplace Equation Research Articles

Probing the surface forces between air bubbles and bitumen via direct force Measurements: Effects of aqueous chemistry

The surface interactions of air bubbles and other components (e.g., particles, oil droplets) significantly influence the operation efficiency of a variety of engineering processes such as oily water treatment, bitumen extraction and flotation. Herein, the surface interactions of air bubbles with two types of Athabasca bitumen samples in aqueous solutions of varying pH, salinity, type of cations and in the presence of surfactants have been systematically characterized using a bubble probe atomic force microscope (AFM) technique. AFM imaging has revealed that exposure to high concentrations of NaCl and CaCl2 solutions or alkaline environments causes roughening of the bitumen surfaces. The results of surface force measurements demonstrate that the interaction and attachment behaviors between bubbles and bitumen are significantly affected by ionic strength, solution pH, and the presence of surfactants. The experimental force measurement results could be accurately described by a theoretical model that incorporates Reynolds lubrication theory and augmented Young-Laplace equation, with the inclusion of disjoining pressure. In low-salinity conditions, the bubble-bitumen interaction is dominated by electric double layer (EDL) repulsion, which prevents surface attachment. This effect is more pronounced at elevated pH conditions. In high-salinity solutions, however, the EDL interactions are significantly reduced, and the hydrophobic interaction becomes the dominant factor, overcoming the van der Waals repulsion and leading to the attachment of bubbles to bitumen surfaces. Raising aqueous pH weakens the bubble-bitumen hydrophobic interaction, whereas the introduction of calcium ions strengthens this interaction, resulting in enhanced surface attachment. Interestingly, even in high-salinity conditions, the presence of a small number of surfactants can inhibit bubble-bitumen contact, mainly caused by reduced hydrophobic attraction and increased steric repulsion. This work provides valuable nanoscale insights into how bubbles and bitumen interact in intricate aqueous environments, and the results show practical implications for controlling similar interfacial phenomena in various engineering processes.

Analysis of Liquid Film Evaporation in Porous Particles: Toward Optimal Wick Parameters for Heat Transfer in Heat Pipes

Abstract Evaporation of working fluids inside capillary wicks determines the heat transfer capability of heat pipes. However, the relationship between wick parameters and evaporative heat transfer remains unclear. To establish a correlation between wick parameters of sintered porous particles and evaporation characteristics, a boundary condition model was developed, incorporating wick parameters such as particle radius (R), particle distance (d), apparent contact angle (θa), and initial liquid height (H). In the absence of a significant size effect, the profile of the liquid–vapor interface was determined using the boundary model by numerically solving the augmented Young–Laplace equation. Ammonia was used as an example to investigate evaporation characteristics. The curvature radius of the intrinsic meniscus (Re) was found to serve as a bridging factor between these wick parameters and evaporation characteristics. When Re exceeded 40.3 μm, a limitation in evaporative heat transfer within the thin film region was observed. The relationship between R, d, θa, and H was quantitatively described based on this evaporative heat transfer limit. Furthermore, a nondimensional analysis of the governing equation for the evaporating liquid film profile was conducted, yielding an influencing factor (λ) that governed the thin film profile. The proposed model and its outcomes could offer valuable theoretical insights for the structural design of sintered porous particles, the optimization of surface modification levels, and the determination of the appropriate working fluid charging ratio during the manufacturing process of heat pipes.

Experimental and theoretical investigation of the impact of crude-oil on the wettability behavior of calcite and silicate due to low salinity effect

Wettability alteration is recognized as the main responsible mechanism for enhanced oil recovery during low salinity water flooding (LSWF) in both carbonates and sandstones. However, there is still a lack of understanding about the possible role of oil type on rock wettability alteration during LSWF. In the current study, contact angle (CA), interfacial tension (IFT), and zeta potentials for both oil/brine and rock/brine interfaces are measured for rock/brine/crude oil systems in a wide range of salinity of seawater. Two different crude oil samples and both calcite and silicate as good end-members of carbonate and sandstones are investigated. For oil A, the CA decreases with brine dilution; however, for oil B, the CA showed almost the opposite trend vs. salinity. The increased water-wetness of silicate compared to calcite surface was more highlighted in lower salinity. The results of zeta potentials showed that diluting seawater (SW) reduced the zeta potentials of rock/brine and oil/brine in all systems. The changes in zeta potential suggest that more dilution shall lead to more water-wetness, which is not in agreement with the CA behavior of two minerals in the case of crude oil B. Based on the augmented Young-Laplace equation, it was demonstrated that there is a good correlation between the IFT and the wettability, especially for calcite minerals. To shed light on the competition between the IFT and the EDL force, a comprehensive model was created to predict the CA results by coupling the surface complexation model (SCM), the DLVO theory, and the Young-Laplace equation. The coupled model successfully predicted the experimental contact angle for both crude oil and rock samples. Analyzing the disjoining pressure curves showed that due to the attractive EDL forces of calcite rocks, the oil/brine IFT solely controls the calcite wettability behavior with salinity. However, for silicate substrates, the high repulsive EDL forces are the main reason for the rock water-wetness at low salinity brines.

Unraveling the hydrophobic interaction mechanisms of hydrocarbon and fluorinated surfaces

HypothesisNumerous hydrocarbon and fluorine-based hydrophobic surfaces have been widely applied in various engineering and bioengineering fields. It is hypothesized that the hydrophobic interactions of hydrocarbon and fluorinated surfaces in aqueous media would show some differences. ExperimentsThe hydrophobic interactions of hydrocarbon and fluorinated surfaces with air bubbles in aqueous solutions have been systematically and quantitatively measured using a bubble probe atomic force microscopy (AFM) technique. Ethanol was introduced to water for modulating the solution polarity. The experimental force profiles were analyzed using a theoretical model combining the Reynolds lubrication theory and augmented Young-Laplace equation by including disjoining pressure arisen from the Derjarguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions (i.e., hydrophobic interactions). FindingsThe experiment results show that the hydrophobic interactions were firstly weakened and then strengthened by increasing ethanol content in the aqueous media, mainly due to the variation in interfacial hydrogen bonding network. The fluorinated surface exhibited less sensitivity to ethanol than hydrocarbon surface, which is attributed to the presence of ordered interfacial water layer. Our work reveals the different hydrophobic effects of hydrocarbon and fluorinated surfaces, with useful implications on modulating the interfacial interactions of relevant materials in various engineering and bioengineering applications.

Numerical Analysis of the Deformation of Aqueous Drop Under Uniform Electric Field

This article presents a numerical analysis of the deformation of an aqueous drop in an oil phase under electric field. The configuration of analysis is a sessile aqueous drop located on an electrode. We use the charge simulation method (CSM) to calculate the electric field in the configuration. The drop profile is determined by solving the augmented Young–Laplace equation. The solution is obtained by iteratively adjusting the drop contour and the fictitious charge for the CSM. Experiments were carried out to observe the behavior of an aqueous sessile drop in a parallel electrode system. The comparison between the experimental and numerical results shows a good agreement of the drop profiles for a wide range of the applied electric field. The calculated critical electric field of drop instability is lower than the value from the experiments by 4%. We employ the numerical analysis to clarify the effects of drop size, interfacial tension coefficient, and mass density of the oil phase on the deformation and the critical electric field of the aqueous drop.

Investigation of interface profiles in meshed wicks and related evaporation characteristics

The porous wick in a heat pipe determines the working fluid capillary replenishment ability and heat transfer process. To study the evaporation characteristics of meshed wicks fabricated with wires of micron-scale, a mathematical model based on the augmented Young-Laplace equation and molecular kinetic theory to predict the evaporation interface profile is developed, and the Marangoni effect and slip velocity in the boundary are considered. The evaporation interface can be divided into the thin-film region and intrinsic meniscus region according to the ratio of capillary pressure and disjoining pressure. A new solution method considering the constraints at the intersection of the two regions to obtain the interface profile is proposed and validated. Based on the two-dimensional results, the area and heat transfer rates of the two regions formed in the meshed wicks are calculated by integrating along the four side wires. Then, the evaporation characteristics of the thin-film region, including the pressure and thermal resistance distribution, are studied. Finally, the influence of the Marangoni effect, superheat, wire spacing, interface pressure difference and slip velocity on the interface profile and heat transfer of these two regions are discussed.

Probing Hydrophobic Interactions between Polymer Surfaces and Air Bubbles or Oil Droplets: Effects of Molecular Weight and Surfactants.

Hydrophobic interaction plays an important role in numerous interfacial phenomena and biophysical and industrial processes. In this work, polystyrene (PS) was used as a model hydrophobic polymer for investigating its hydrophobic interaction with highly deformable objects (i.e., air bubbles and oil droplets) in aqueous solutions. The effects of polymer molecular weight, solvent (i.e., addition of ethanol to water), the presence of surface-active species, and hydrodynamic conditions were investigated, via direct surface force measurements using the bubble/drop probe atomic force microscopy (AFM) technique and theoretical calculations based on the Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. It was found that the PS of low molecular weight (i.e., PS590 and PS810) showed slightly weaker hydrophobic interactions with air bubbles or oil droplets, as compared to glassy PS of higher molecular weight (i.e., PS1110, PS2330, PS46300, and PS1M). The hydrophobic interaction between PS and air bubbles in a 1 M NaCl aqueous solution with 10 vol % ethanol was weaker than that in the bare aqueous solution. Such effects on the hydrophobic interactions are possibly achieved by influencing the structuring/ordering of water molecules close to the hydrophobic polymer surfaces by tuning the surface chain mobility and surface roughness of polymers. It was found that the addition of three surface-active species, i.e., cetyltrimethylammonium chloride (CTAC), Pluronic F-127, and sodium dodecyl sulfate (SDS), to the aqueous media could suppress the attachment of the hydrophobic polymer and air bubbles or oil droplets, most likely caused by the additional steric repulsion due to the adsorbed surface-active species at the bubble/polymer/oil interfaces. Our results have improved the fundamental understanding of the interaction mechanisms between hydrophobic polymers and gas bubbles or oil droplets, with useful implications on developing effective methods for modulating the related interfacial interactions in many engineering applications.

Liquid imbibition in tight rocks: The role of disjoining pressure

Modelling wettability of tight rocks is challenging due to their complex pore networks, sub-micron pore throats, and organic pores. The experimental results show oil-wet behavior of dry core plugs. Assuming different flow paths for oil and water imbibition, the ratio between oil and brine capillary pressure calculated using imbibition profiles is from 0.67 to 1.76, while that calculated by Young-Laplace model is around 0.5. The higher oil imbibition cannot be completely explained by the conventional Young-Laplace model. Therefore, we apply Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory to evaluate intermolecular forces among oil, water, and rock surface by calculating disjoining pressure (Π d ). For liquid imbibition in dry samples, the Π d calculations show that the attraction between rock and oil is stronger than that between rock and water, explaining the higher oil imbibition into the core samples. The ratio between oil and brine capillary pressure calculated by the augmented Young-Laplace equation, which considers Π d , is closer to that calculated using the imbibition data. The excess oil imbibition is also due to hydrocarbon coating on inorganic pores and different flow paths for oil and water. The attraction between rock and oil increases if we consider more percentage of pores coated by residual hydrocarbon. To explain the water imbibition into oil-saturated core plugs, we evaluate the stability of the oil and water films covering the rock surface. The calculated Π d profiles suggest that quartz is more water-wet compared with other minerals. The thin water film covering quartz becomes more stable as the film thickness increases, helping oil production from oil-saturated pores composed of quartz. We also calculate Π d for brine with different salinities. Generally, for a rock surface-water-oil system, Π d increases by decreasing water salinity, suggesting more stable water film. • The disjoining pressure calculations explain the higher oil imbibition compared with brine imbibition. • The thin water film covering quartz is stable, and it becomes more stable by increasing its thickness. • The water film on rock is more stable with lower salinity, explaining the higher oil recovery for imbibition with low-salinity water.

Micromechanical description of adsorptive-capillary stress in wet fine-grained media

The aim of this paper is to investigate the effect of an adsorbed water layer on the mechanical behavior of fine-grained wet granular materials in the pendular regime with isolated capillary liquid bridges. The adsorbed water forms a thin liquid film tightly bound to a particle’s surface equilibrated by a so-called “disjoining pressure”. In a stress transmission analysis, this disjoining pressure concept is embedded in the so-called Augmented Young-Laplace equation to account for thin film interfacial interactions. Using a homogenization technique for upscaling the micro-scale physics, an adsorptive-capillary stress tensor is derived whose discrete representation reveals a new interparticle cohesive force. In the presence of adsorbed layers, it is shown that the new liquid bridge profile, as numerically solved from the Young-Laplace equation, leads to a higher cohesive interparticle force and rupture distance. The proposed adsorptive-capillary stress tensor is further implemented within a discrete element modeling framework. As such, the evolutions of microstructure, stress tensors, and shear strength are illustrated during suction-controlled triaxial simulations. Our numerical results demonstrate that adsorbed layers have a notable effect on the mechanical behavior of fine-grained materials, particularly at higher suctions.

The effect of surface morphology on the rate of phase change of micron and sub-micron sized 2-D droplets

ABSTRACT Heat transfer via phase change is a major contributor to heat removal in numerous engineering applications. Thin films of liquid result in increased heat transfer due to a reduction of conduction resistance, in addition the pressure jump at the liquid-vapor interface also affects the rate and direction of the rate of phase change. Because of these effects the morphology of the substrate surface is expected to affect the film shape, hence heat transfer, especially in thin films. In this study, the influence of surface characteristics on the rate of phase change from micron- and submicron-sized 2D droplets – i.e. films extending to infinity – forming on a substrate are modeled. Surface film profiles are generated on both flat and nonflat surfaces, triangular or wavy in nature, and a kinetic model for quasi-equilibrium phase change is applied. In the case of wavy surfaces, the surface is assumed to be a harmonic wave with an amplitude equal to the surface roughness and a wavelength corresponding to values commonly encountered in applications. Due to the presence of intermolecular forces at the contact line, which renders the solution of the augmented Young-Laplace equation stiff, an implicit scheme is employed for the numerical integration. To verify the method, the predictions of a molecular dynamics (MD) simulation of a nano-sized droplet present on a V-grooved surface are compared to the continuum model. The augmented Young-Laplace equation is solved numerically along with a phase change model originating from kinetic theory to calculate the shape of the two-phase interface forming the droplet and study the effect of various parameters on the rate of phase change. Results are obtained for droplets with liquid pressures higher and lower than that of vapor, resulting in opposite contribution to phase change due to the pressure jump at the interface. The results show that the heat-transfer rate can be substantially altered due primarily to the combined effects of surface morphology and disjoining pressure. It is also concluded that wavy surfaces with short amplitudes are preferable to ones with longer amplitudes for enhancing the rate of evaporation or condensation.

A novel transient thermohydraulic model of micro-channel heat sink

The purpose of this work is to develop an analytical model for prediction of the thermal fluid performance of a micro-channel heat sink by applying liquid thin-film theory. For this purpose, a one-dimensional transient model has been developed for a single channel of micro-channel heat sink and a series of numerical simulation was performed for various operating conditions. Mass, momentum and energy equations were applied separately for the vapor and liquid phases to predict more effective physical performance of the transient behavior. As a result, the axial distributions of mass flow, pressure, and temperature for the working fluid were obtained for vapor and liquid in the micro-channel. In particular, the phase change interface profile with the liquid thin-film was obtained using an augmented Young Laplace equation. Consequently, the interface areas of heat and mass transfer occupied by the liquid and vapor were predicted and incorporated into the governing equations of each phase. The analytical model was validated by comparison of its numerical solutions with experimental results. The discrepancy between the experimental and numerical results for the axial wall temperature was less than 4 °C, and that for the transient time to reach a steady-state wall temperature was within 1 sec. Through a series of performance simulations for a micro-channel model with pure water as the working fluid, transient response of the wall temperature, liquid film thickness, mass flow rate, liquid pressure, and vapor and liquid temperatures were investigated. The model developed in this study might be utilized for more refined performance prediction of a micro-channel heat sink.

Electric field effect on the contact angle for non-wetting drops

A microscopic model is formulated concerning the electrowetting of an electrically conducting drop on a dielectric substrate. The interaction energy between the drop and substrate includes both van der Waals attractive forces and Born repulsive forces resulting in an equilibrium gap. An augmented Young–Laplace equation is derived and used as the basis for calculations of wetting phenomena both with and without an applied voltage. In the absence of an electric field, a well-defined Young’s angle is established at a distance from the meniscus incipience that is less than 100 times the equilibrium gap. An expression for Young’s angle is determined showing its dependence on material properties of the system. With an electric field applied, the meniscus angle changes continuously from the three-phase line (TPL), where it is near zero, until after a distance of at least ten times the thickness of the dielectric where the Lippmann angle is established. Therefore, the initial angle is not the Lippmann angle and care must be taken in the interpretation of measurements of an apparent contact angle.

Effect of time-varying magnetic field on metal droplet profiles

A nonmagnetic metal droplet with dynamic interfaces under a time-varying magnetic field was considered. Considering that the thermal effect of the magnetic field and the droplet evaporation were disregarded, we obtained the magnetically augmented Young–Laplace equation theoretically according to the normal stress balance principles. The droplet contact angle was further determined according to the droplet volume conservation. According to the curvature and contact angle, the droplet profile was mathematically determined. Results showed that a downward magnetic force caused droplet contraction and an upward force caused expansion. The increase in surface tension hindered the droplet spreading without affecting the change trend of droplet shape parameters. The increase in angular frequency (ω) decreased the variation amplitude of the droplet curvature and contact angle, and the increase in damping factor (τ) slowed down the decay of the droplet curvature and contact angle.

A novel transient thermohydraulic model of a micro heat pipe

A transient analysis model for predicting the heat and mass transfer performance in micro heat pipes is presented in this paper. The mass, momentum, and energy equations were separately applied for the vapor and liquid phases to predict the physical performance of the transient response more effectively. As a result, the axial distributions of the mass flow, pressure, and temperature were obtained for the vapor and liquid in a micro heat pipe. In particular, the profile of the liquid–vapor interface was obtained with liquid thin-film theory using the augmented Young–Laplace equation. Consequently, the interfacial areas for heat and mass transfer were predicted and incorporated into the governing equations of each phase. The analytical model was validated by comparing its solutions with experimental results. The discrepancy between the experimental and numerical results for the temperature difference between the evaporator and the condenser was less than 0.5 °C, which represents moderate accuracy.

The effect of disjoining pressure on the shape of condensing films in a fin-groove corner

Thin film condensation is commonly present in numerous natural and artificial processes. Phase-change driven passive heat spreaders such as heat pipes, which are widely used in electronics cooling, employ a continuous condensation process at the condenser region. When the wick structure of a heat pipe is composed of grooves, the top surfaces of the walls (fins) located between consecutive grooves function as the major source of condensation and the condensate flows along the fin top into the grooves. Modeling of this condensation problem is vital for the proper estimation of condensation heat transfer, which constitutes the basis for the overall performance of a heat pipe together with the evaporation process. In the current study, a solution methodology is developed to model the condensation and associated liquid flow in a fin-groove system. Conservation of mass and momentum equations, augmented Young-Laplace equation and Kucherov-Rikenglaz equation are solved simultaneously to calculate the film thickness profile. The model proposed enables the investigation of the effect of disjoining pressure on the film profile by keeping the fin-groove corner, where the film becomes thinnest, inside the solution domain. The results show that dispersion forces become effective for near isothermal systems with sharp fin-groove corners and the film profile experiences an abrupt change, a slope break, in the close proximity of the corner. The current study is the first computational confirmation of this behavior in the literature.

Investigation of modified Water chemistry for improved oil recovery: Application of DLVO theory and surface complexation model

It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine. A typical approach is diluting the formation water to a specific lower salinity. However, recent experimental studies report the adverse effect of formation water dilution on oil recovery for specific oil/brine/rock systems. The adverse effect depends on the interactions within the system and is more pronounced in carbonates. In this study, we investigated the effect of water composition on the performance of low salinity water injection by considering the complex interaction of oil, brine, and rock system.A surface complexation model (SCM) is developed to calculate the zeta-potential at oil and rock surfaces. Considering a water film between oil and rock and using DLVO theory, attractive/repulsive forces between oil/brine and brine/rock interfaces are calculated. Contact angle is predicted employing the augmented Young-Laplace equation. Our zeta potential calculations based on the SCM reproduced the experimental data of oil/brine and brine/calcite zeta potential measurements. Our contact angle calculations using the DLVO theory and the augmented Young-Laplace equation accurately estimated the dynamic trend of contact angle during low salinity flood. Modeling wettability alteration as a function of contact angle was sufficient to predict the low salinity effect. The developed model is implemented in a comprehensive compositional reactive transport simulator to validate the proposed approach.

Unraveling Interaction Mechanisms between Molybdenite and a Dodecane Oil Droplet Using Atomic Force Microscopy

Molybdenite (MoS2) is a mineral that has drawn great interest because of its potential application in various fields. To facilitate the flotation of molybdenite, the mineral pulp is commonly treated with nonpolar oil additives to promote hydrophobicity and to form an oil bridge between ultrafine molybdenite particles for agglomeration. In this study, dodecane was chosen as a model oil to investigate the flotation mechanisms of molybdenite with nonpolar oil. The interaction forces between a micrometer-sized dodecane droplet and the molybdenite basal plane in various electrolyte solutions were directly measured by the atomic force microscope droplet probe technique. The effects of added salts, ionic strength, and solution pH on interaction forces were evaluated by considering van der Waals, electrical double-layer (EDL), and hydrophobic forces. The experimentally measured force curves were found to agree well with the Reynolds lubrication model and the augmented Young-Laplace equation. The results show that the competition between repulsive EDL forces and attractive hydrophobic forces was directly responsible for oil-molybdenite attachment behavior. High pH and low salinity (<24 mM NaCl) led to strong repulsive EDL forces, which stabilized the interaction and prevented the attachment of oil to molybdenite. Both low pH and high salinity facilitated the attachment of oil to molybdenite through the depression of EDL force, allowing attractive hydrophobic force to dominate. The hydrophobic attraction was quantified with an exponential decay length of 1.0 ± 0.1 nm. Furthermore, calcium ions decreased the magnitude of the surface potentials of both oil and molybdenite more than that seen with the same ionic strength of sodium ions, suggesting the suppressed EDL repulsion. This study provides quantitative information about the surface forces between oil and the molybdenite basal plane and an improved understanding of the fundamental interaction mechanisms governing molybdenite recovery by mineral flotation.

A numerical modeling for the steady-state performance of a micro heat pipe using thin liquid film theory

A numerical analysis on heat and mass transfer in a micro heat pipe was performed in this work. Mass, energy, and momentum equations were applied to vapor and liquid phases under steady-state operation in the numerical model. As a result, the trends in mass flow, pressure distribution, and temperature distribution for the working fluid circulating inside the micro heat pipe were obtained for vapor and liquid, respectively. In particular, the vapor-liquid interface shape obtained with a thin liquid film through augmented Young-Laplace equation and areas for heat and mass transfer of liquid and vapor from the vapor-liquid interface thickness were predicted. These areas were applied to solution on the governing equations for vapor and liquid. The numerical model was validated by experimental results. The errors between the experimental and numerical results for the average temperature difference of the evaporator and condenser were found to be less than 1 °C. The errors for thermal resistance had maximum and minimum values of 15.2% and 3.8%, respectively.

Field-Assisted Contact Line Motion in Thin Films.

The balance of intermolecular and surface forces plays a critical role in the transport phenomena near the contact line region of an extended meniscus in several technologically important processes. Externally applied fields can alter the equilibrium and stability of the meniscus with concomitant effects on its shape and spreading characteristics and may even lead to an oscillation. This feature article provides a detailed account of the present and past efforts in exploring the behavior of curved thin liquid films subjected to mild thermal perturbations, heat input, and electrical and magnetic fields for pure as well as colloidal suspensions, including the effects of particle charge and polarity. The shape-dependent intermolecular force field has been evaluated in situ by a nonobtrusive optical technique utilizing the interference phenomena and subsequent image processing. The critical role of disjoining pressure is identified along with the determination of the Hamaker constant. The spatial and temporal variations of the capillary forces are evaluated for the advancing and receding menisci. The Maxwell-stress-induced enhanced spreading during electrowetting, at relatively low voltages, and that due to the application of a magnetic field are discussed with respect to their distinctly different characteristics and application potentials. The use of the augmented Young-Laplace equation elicited additional insights into the fundamental physics for flow in ultrathin liquid films.

Determination of the interaction mechanism of 10 µm oil-in-water emulsion droplets using optical tweezers

A comprehensive understanding of the stability of an emulsion relies on a quantitative understanding of the dynamic interaction forces between the dispersed emulsion droplets. Microscale droplets have been widely used in various applications, for e.g., in food, cosmetics, controlled drug release, and biology. The dynamic interaction forces between two deformable emulsion droplets in the size range of 20–200 µm have been well-analysed using bubble/drop probe atomic force microscopy, whereas those of the emulsion droplets below 10 µm are rarely studied. In this work, we quantify the interaction forces between a pair of 1,6-hexanediol diacrylate (HDDA) droplets with a 10 µm diameter in an aqueous phase using optical tweezers (NanoTracker™ 2). By capturing two oil droplets in two separate optical traps and bringing them into close proximity, their interaction forces can be measured as a function of the separation distance. The force profiles are analysed using a theoretical model based on the augmented Young–Laplace equation that includes the effects of disjoining pressure. The interaction forces between two 10 µm HDDA oil droplets with SDS molecules adsorbed at their interfaces could be well-described using the classical Derjaguin–Landau−Verwey–Overbeek theory. This work demonstrates a useful methodology to quantify the interaction forces between microscale emulsion droplets with pN force precision, providing a deeper understanding of the stabilization mechanism of O/W emulsions and can be extended to many other emulsion systems.This work has been selected by the Editors as a Featured Cover Article for this issue.