Liquid-air Interface Research Articles

Small scale model for predicting transportation-induced particle formation in biotherapeutics

Understanding protein adsorption and aggregation at the air-liquid interfaces of protein solutions is an important open challenge in biopharmaceutical, medical, and biotechnological applications, among others. Proteins, being amphiphilic, adsorb at the surface, partially unfold, and form a viscoelastic film through non-covalent interactions. Mechanical agitation of the surface can break this film up, releasing insoluble protein particles into the solution. These aggregates are usually highly undesirable and even toxic in cases, such as for biopharmaceutical application. Therefore, it is imperative to be able to predict the behavior of such solutions undergoing surface agitation during handling, usually transport or mixing. We apply the findings on the viscoelastic protein film, formed at the air-liquid interface, to the prediction of surface mediated aggregation in selected protein solutions of direct biopharmaceutical relevance. Our broad study of Brewster angle microscopy and aggregation monitoring across multiple size ranges by micro-flow imaging, light scattering, and size exclusion chromatography shows that formation of protein particles is driven by the adsorption rate as compared to the rate of surface turnover and that surface film dynamics in the quiescent phase directly affect aggregation. We demonstrate how these learnings can be directly applied to the design of a novel small scale biopharmaceutical stability study, simulating relevant transport conditions. More generally, we show the impact of adsorption dynamics at the air-liquid interface on the stability of a distinct protein solution, as a general contribution to understanding different colloidal and biological interfacial systems.

Freestanding Hydrogen-Bonded Organic Framework Membrane for Efficient Wound Healing.

Hydrogen-bonded organic frameworks (HOFs) are emerging as multifunctional materials with exceptional biocompatibility, abundant active sites, and tunable porosity, which are highly beneficial for advanced wound care. However, a significant challenge involves transforming pristine HOFs powders into lightweight, ultrathin, freestanding membranes compatible with soft biological systems. Herein, the study successfully develops shape-adaptive HOF-based matrix membranes (HMMs) using a polymer-assisted liquid-air interface technique. The HMMs conform seamlessly to tissues of different sizes and shapes, effectively stopping bleeding, and provide high water-vapor permeability. Notably, both in vitro and in vivo studies with mice wound models demonstrated that these tissue-conformable HMMs significantly accelerate wound healing by modulating the inflammatory environment of the injured tissue and promoting rapid re-epithelialization. Furthermore, RNA-seq analysis and mechanistic studies revealed that HMMs effectively reduce inflammation and facilitate the tissue transition from the proliferative stage to the remodeling stage of skin development. This work not only opens up new avenues for advanced wound care materials but also establishes a foundation for hybridizing HOFs with polymers for a wide range of potential applications.

Numerical investigation into the transition of electrohydrodynamic spraying modes and behaviors

Electrohydrodynamic (EHD) spraying is an interesting phenomenon where the liquid subjected to an electrical stress deforms into an electrified liquid drop, a thin liquid jet, or the so-called Taylor cone, which is also highly complicated owing to its various spraying modes and behaviors. Due to the lack of critical information such as the electric charge density and internal velocity profile, the underlying physics behind the transition of different EHD spraying modes are still not adequately understood. In light of this, we conducted a numerical investigation into the transition of EHD spraying modes and behaviors under the three most important operating parameters including electric voltage, nozzle height, and liquid flow rate. Four typical spraying modes, namely, dripping, cone-jet, multi-jet, and jetting, are observed. From the numerical results, we obtained the voltage distribution in the environment, electric charge density at the liquid–air interface, and velocity profile inside the liquid, which help us to comprehensively analyze and explicate the influences of these three parameters on the transition of spraying modes and behaviors. This eventually leads us to a spraying mode map showing the correlation between the spraying modes and the electric Bond number. To the best of our knowledge, this is the first numerical work focusing on the transition of EHD spraying mode, from which we intend to expand the knowledge of this interesting phenomenon.

Motion and Orientation of Janus Spherical Particles at a Liquid-Air Interface Governed by the Moses Effect.

We investigated the motion of spherical polystyrene/polypyrrole-coated polystyrene Janus particles placed at an air/saline interface and driven by a permanent magnetic field of ca. 0.5 T. For the sake of comparison, the motion of pure floating polystyrene particles was studied. Both kinds of the studied particles moved toward the magnet and stopped at the boundary of the near-surface well produced by the magnetic field. The Moses effect-driven motion of floating Janus particles was analyzed and investigated under different strengths of the magnetic field and salt concentrations. The study of the Janus particle displacement led to the development of a unified theoretical framework explaining the mechanism of the motion. This framework predicts that the motion of particles placed at an air-salt solution interface is not only dictated by magnetic energy but also intricately influenced by the interplay of factors, including the curvature of the interface caused by the static magnetic field, gravitational potential, and capillary forces. The orientation of the particles was observed. A qualitative explanation of the observed phenomena is suggested. The investigated process has potential for the self-assembly of particles placed at the liquid/air interface.

Shear-imposed falling film on a vertical moving plate with disrupted time-reversal

We propose a mathematical model to study the stability and dynamics of a shear-imposed thin film flow on a vertical moving plate, incorporating the influence of odd viscosity. This odd viscosity effect is vital in conventional fluids when there is a disruption in time-reversal symmetry. Our motivation to study the dynamics with odd viscosity arises from recent studies (Kirkinis & Andreev, vol. 878, 2019, pp. 169–189; Chattopadhyay & Ji, vol. 455, 2023, pp. 133883) where the odd viscosity effectively reduces flow instabilities under different scenarios. Utilizing a long wave perturbation method, we derive a nonlinear evolution equation at the liquid–air interface, which is influenced by the motion of the vertical plate, imposed shear, odd viscosity, and inertia. We first perform a linear stability analysis of the model to get firsthand information on various flow parameters. Three distinct conditions for the vertical plate, quiescent, upward-moving, and downward-moving, are considered, accounting the imposed shear and odd viscosity. Additionally, employing the method of multiple scales, we conduct a weakly nonlinear stability analysis for the traveling wave solution of the evolution equation and explore its bifurcation analysis. The bifurcation analysis reveals the existence of subcritical unstable and supercritical stable zones for crucial flow parameters: odd viscosity, imposed shear, and motion of the vertical plate. Both linear and weakly nonlinear stability analyses demonstrate that the destabilizing effect induced by the upward motion of the vertical plate can be alleviated by applying uphill shear, while the destabilizing effect of downhill shear can be mitigated when the vertical plate is in a downward motion. Moreover, we define an eigenvalue problem that mirrors the Orr–Sommerfeld (OS) model for analyzing normal modes and identifying the critical Reynolds number. We investigate the dynamics of surface waves through numerical solutions of the OS eigenvalue problem using the Chebyshev spectral collocation method. We observe the consistent enhancement of stabilization in the presence of odd viscosity. In the low to moderate Reynolds number range, vertical plate motion and odd viscosity show similar behavior in OS analysis, while imposed shear exhibits distinct changes. The Benney-type model does not agree with the OS problem when the Reynolds number is moderate with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity. However, when the Reynolds number is low with or without the three key parameters: vertical plate motion, imposed shear, and odd viscosity, the Benney-type model agrees with the OS. Further, numerical simulations of the evolution equation corroborate the results obtained from linear stability, weakly nonlinear stability, and OS analyses. Finally, the Hopf bifurcation analysis of the fixed point reveals that the wave speed is influenced by both the motion of the plate and the imposed shear while it remains independent of odd viscosity.

Droplet Microfluidic Method for Estimating the Dynamic Interfacial Tension of Ion-Crosslinked Sodium Alginate Microspheres.

The research focuses on optimizing the production of hydrogel microspheres using droplet microfluidics for pharmaceutical and bioengineering applications. A semiempirical method has been developed to predict the dynamic interfacial tension at the interface of ion-cross-linked sodium alginate microsphere-sunflower oil modified with glacial acetic acid and Tween 80 surfactant. These microspheres are produced in a small-scale coaxial device that is manufactured using affordable DLP/LCD 3D printing technology with a transparent photopolymer. The method was tested to design the minireactor in the device, which allows for the production of fully cross-linked microspheres that are ready for use at the output of the reactor without additional cross-linking steps in the microsphere collector. The mathematical expression for estimating the interfacial tension at the moment of formation of a hydrogel microsphere includes the Reynolds number for a two-phase liquid, the Ohnesorge number, and the surface tension at the liquid-air interface for continuous medium flow (modified oil). The reliability of the prediction is confirmed for continuous medium and dispersed phase flow rates of 0.8-3.2 and 0.01-0.08 mL/min, respectively. The evolution of the interfacial tension from the moment the microspheres formed and the estimated ultimate interfacial tension in a cross-linked hydrogel-modified oil system contributed to the reliable determination of the linear size of a minireactor. The ultimate interfacial tension of 76.5 ± 0.3 mN/m was determined using the Young-Laplace equation, which is based on measuring the surface free energy of the hydrogel as soft matter using the Owens-Wendt method. Additionally, the equilibrium static contact angle of the fully cross-linked hydrogel surface wetted with oil is measured using the sessile drop method. From a practical perspective, a method for optimizing and streamlining the high-tech manufacturing of cross-linked polymer microspheres and mini- and microchannel devices for use in bioengineering and pharmaceutical applications is suggested.

Dynamics of particle aggregation in dewetting films of complex liquids

We consider the dynamic wetting and dewetting processes of films and droplets of complex liquids on planar surfaces, focusing on the case of colloidal suspensions, where the particle interactions can be sufficiently attractive to cause agglomeration of the colloids within the film. This leads to an interesting array of dynamic behaviours within the liquid and of the liquid–air interface. Incorporating concepts from thermodynamics and using the thin-film approximation, we construct a model consisting of a pair of coupled partial differential equations that represent the evolution of the liquid film and the effective colloidal height profiles. We determine the relevant phase behaviour of the uniform system, including finding associated binodal and spinodal curves, helping to uncover how the emerging behaviour depends on the particle interactions. Performing a linear stability analysis of our system enables us to identify parameter regimes where agglomerates form, which we independently confirm through numerical simulations and continuation of steady states, to construct bifurcation diagrams. We obtain various dynamics such as uniform colloidal profiles in an unstable situation evolving into agglomerates and thus elucidate the interplay between dewetting and particle aggregation in complex liquids on surfaces.

Enhanced insights into paired droplet evaporation dynamics on heated substrates: Unveiling the role of convection and diffusion

This study aims to examine the evaporation characteristics of single and multiple droplets on a heated substrate. By utilizing a multi-syringe pump, deionized water droplets were precisely deposited on a copper substrate, ensuring uniformity and accuracy in the experimental setup. The shadowgraph technique was instrumental in determining the droplet contact angle and volume with exceptional clarity and precision. This work numerically predicted the vapor distribution and local evaporation flux across the liquid-air interface. A critical assessment of the role of natural convection at varying substrate temperatures was performed by contrasting diffusion-only cases with those incorporating both diffusion and convection. The findings reveal that the droplet pinning motion remains unchanged across different distances between droplets and various substrate temperatures, indicating that neither vapor accumulation nor substrate temperature significantly influences the behavior of the contact line. Notably, the study identifies a reduction in the evaporation rate of closely positioned paired droplets, related to a shielding effect. However, with increasing substrate temperature, the role of natural convection was found to become more pronounced, effectively reducing the overall evaporation time for both single and paired droplets, thus facilitating a quicker evaporation process.

Path Integral Simulations of Condensed-Phase Vibrational Spectroscopy.

Recent theoretical and algorithmic developments have improved the accuracy with which path integral dynamics methods can include nuclear quantum effects in simulations of condensed-phase vibrational spectra. Such methods are now understood to be approximations to the delocalized classical Matsubara dynamics of smooth Feynman paths, which dominate the dynamics of systems such as liquid water at room temperature. Focusing mainly on simulations of liquid water and hexagonal ice, we explain how the recently developed quasicentroid molecular dynamics (QCMD), fast-QCMD, and temperature-elevated path integral coarse-graining simulations (Te PIGS) methods generate classical dynamics on potentials of mean force obtained by averaging over quantum thermal fluctuations. These new methods give very close agreement with one another, and the Te PIGS method has recently yielded excellent agreement with experimentally measured vibrational spectra for liquid water, ice, and the liquid-air interface. We also discuss the limitations of such methods.

Colloidal deposits from evaporating sessile droplets: Coffee ring versus surface capture

Suppression of the coffee ring effect is desirable in many industrial applications which utilize colloidal deposition from an evaporating liquid. Here we focus on the role of particle arrest at the liquid-air interface (surface capture) which occurs at high evaporation rates. It is known experimentally that this phenomenon inhibits particles from reaching the contact line, leading to a deposit which is closer to uniform. We are able to describe this effect using a simple 1D modeling framework and, utilizing asymptotic theory, parametrize our model by the ratio of the vertical advection and diffusion timescales. We show that our model is consistent with existing frameworks for small values of this parameter, but also predicts the surface layer formation seen experimentally at high evaporation rates. The formation of a surface layer leads to a deposit morphology which mimics the evaporative flux density and so is closest to uniform when evaporation has a constant strength across the liquid-air interface. Published by the American Physical Society 2024

Effect of casein genetic variants and glycosylation on bovine milk foaming properties

The effects of κ‐casein (κ‐CN) and β‐casein (β‐CN) genetic variant and κ‐CN glycosylation degree (GD, low or high) on interfacial and foaming properties of bovine skim milk were investigated. No significant effect was measured for milks with different ĸ‐CN and β‐CN genetic variants. However, milks of higher GD exhibited lower surface tension, enhanced foamability and differences in secondary protein structure compared to lower GD skim milks. Glycan attachment is believed to affect surface activity and the spread and packing of protein at the foam bubble liquid–air interface, leading to differences in foaming performance.

Enhanced Total Contactless Photothermal Desalination by Translucent Thin Film Coating of Crystalline Nanocellulose.

The innovative approach of harnessing abundant solar energy to facilitate water purification holds great potential for addressing a diverse range of water-related challenges. Utilizing the same method of photothermal desalination is highly promising, sustainable, and cost effective. However, in photothermal desalination, generally, steam is generated at the liquid-air interface. Despite its immense potential, this results in a lower evaporation rate and is prone to salt fouling. Therefore, to address two main challenges, (1) fouling and (2) maximum interfacial temperature (100 °C), here, we report total contactless photothermal desalination by a translucent thin film coating of Crystalline Nanocellulose (CNC). In contactless photothermal desalination, the active photothermal layer remains in no physical contact with the saline water; thus, automatic antifouling and a temperature above the boiling point of water can be achieved for water purification. In this report, we have sustainably extracted CNC from waste sawdust by a sonochemical extraction method using minimal chemicals. Additionally, the sonoextraction method through cavitation helps in the desulfation of CNC. These thermally stable and highly crystalline CNCs are used in making active translucent photothermal active layers for photothermal desalination. CNCs were well characterized by both microscopic and spectroscopic techniques. In the photothermal desalination, the results show an augmented evaporation rate of ∼3.30 kg/m2·h and virtually infinite recyclability for longer usability. Moreover, the integrated setup reported here comprises an independent module with a highly flexible design that mimics the greenhouse effect for a high solar-to-steam output.

Role of Unimers to Polymersomes Transition in Pluronic Blends for Controlled and Designated Drug Conveyance.

This study investigates the nanoscale self-assembly from mixtures of two symmetrical poly(ethylene oxide)-poly(propylene oxide)-pol(ethylene oxide) (PEO-PPO-PEO) block copolymers (BCPs) with different lengths of PEO blocks and similar PPO blocks. The blended BCPs (commercially known as Pluronic F88 and L81, with 80 and 10% PEO, respectively) exhibited rich phase behavior in an aqueous solution. The relative viscosity (ηrel) indicated significant variations in the flow behavior, ranging from fluidic to viscous, thereby suggesting a possible micellar growth or morphological transition. The tensiometric experiments provided insight into the intermolecular hydrophobic interactions at the liquid-air interface favoring the surface activity of mixed-system micellization. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) revealed the varied structural morphologies of these core-shell mixed micelles and polymersomes formed under different conditions. At a concentration of ≤5% w/v, Pluronic F88 exists as molecularly dissolved unimers or Gaussian chains. However, the addition of the very hydrophobic Pluronic L81, even at a much lower (<0.2%) concentration, induced micellization and promoted micellar growth/transition. These results were further substantiated through molecular dynamics (MD) simulations, employing a readily transferable coarse-grained (CG) molecular model grounded in the MARTINI force field with density and solvent-accessible surface area (SASA) profiles. These findings proved that F88 underwent micellar growth/transition in the presence of L81. Furthermore, the potential use of these Pluronic mixed micelles as nanocarriers for the anticancer drug quercetin (QCT) was explored. The spectral analysis provided insight into the enhanced solubility of QCT through the assessment of the standard free energy of solubilization (ΔG°), drug-loading efficiency (DL%), encapsulation efficiency (EE%), and partition coefficient (P). A detailed optimization of the drug release kinetics was presented by employing various kinetic models. The [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] MTT assay, a frequently used technique for assessing cytotoxicity in anticancer research, was used to gauge the effectiveness of these QCT-loaded mixed nanoaggregates.

Surface properties of systems based on amines and (co)polymers of acrylamide at the liquid–air interface

Surface properties of the systems based on amines and acrylamide (co)polymers have been studied depending on the molecular structure of the components in aqueous and saline (sodium chloride) solutions. For the systems of amines with an anionic acrylamide copolymer, a change in the shape of the surface tension isotherm was found. The tendency to change the surface properties is enhanced in systems with an anionic acrylamide copolymer, aliphatic amine and in the presence of a low molecular weight electrolyte.

Exploring the evolution of bacterial cellulose precursors and their potential use as cellulose-based building blocks.

Natural polymers have found increased use in a wider range of applications due to their less harmful effects. Notably, bacterial cellulose has gained significant consideration due to its exceptional physical and chemical properties and its substantial biocompatibility, which makes it an attractive candidate for several biomedical applications. This study attempts to thoroughly unravel the microstructure of bacterial cellulose precursors, known as bioflocculants, which to date have been poorly characterised, by employing both electron and optical microscopy techniques. Here, starting from bioflocculants from Symbiotic Culture of Bacteria and Yeast (SCOBY), we proved that their microstructural features, such as porosity percentage, cellulose assembly degree, fibres' density and fraction, change in a spatio-temporal manner during their rising toward the liquid-air interface. Furthermore, our research identified a correlation between electron and optical microscopy parameters, enabling the assessment of bioflocculants' microstructure without necessitating offline sample preparation procedures. The ultimate goal was to determine their potential suitability as a novel cellulose-based building block material with tuneable structural properties. Our investigations substantiate the capability of SCOBY bioflocculants, characterized by distinct microstructures, to successfully assemble within a microfluidic device, thereby generating a cellulose sheet endowed with specific and purposefully designed structural features.

Structural, Optical, and Mechanical Insights into Cellulose Nanocrystal Chiral Nematic Film Engineering by Two Assembly Techniques.

Iridescent cellulose nanocrystal (CNC) films with chiral nematic nanostructures exhibit great potential in optical devices, sensors, painting, and anticounterfeiting applications. CNCs can assemble into a chiral nematic liquid crystal structure by evaporation-assisted self-assembly (EISA) and vacuum-assisted self-assembly (VASA) techniques. However, there is a lack of comprehensive examinations of their structure-property correlations, which are essential for fabricating materials with unique properties. In this work, we gained insights into the optical, mechanical, and structural differences of CNC films engineered using the two techniques. In contrast to the random self-assembly at the liquid-air interface in EISA, the continuous external pressure in the VASA process forces CNCs to assemble at the filter-liquid interface. This results in fewer defects in the interfaces between tactoids and highly ordered cholesteric phases. Owing to the distinct CNC assembly behaviors, the films prepared by these two methods show great differences in the nanostructure, microstructure, and macroscopic morphology. Consequently, the highly ordered cholesteric structure gives VASA-CNC films a more uniform structural color and enhanced mechanical performance. These fundamental understandings of the relationship of structure-property nanoengineering through various assembly techniques are essential for designing and constructing high-performance chiral iridescent CNC materials.

Interfacial Effects of Nanostructured Doubly Reentrant Surfaces on the Evolution of Local Concentration and Fluid Flow in an Evaporating Droplet.

Surface modification, such as bioinspired nanostructured doubly reentrant surfaces that have presented superhydrophobic wettability even under low-surface-tension liquid, is a very promising technology for controlling droplet dynamics, heat transfer, and evaporation. In this article, we investigate the interfacial effects of nanostructured doubly reentrant surfaces on the flow behaviors and local concentration evolution during the evaporation of an ethanol/water multicomponent droplet. Using particle image velocimetry (PIV) and novel aggregate-induced emission-based (AIE) techniques, the flow patterns and local concentration distributions on both hydrophobic and nanostructured doubly reentrant surfaces were probed and compared. It is found that in addition to the established Marangoni flow-dominated stage, transition stage, and buoyancy-induced flow-dominated stage, a new transition stage and a rolling stage for the nanostructured doubly reentrant surface are detected in the late evaporation period. Differences in the local concentration distribution evolution occur depending on the hydrophobicity of the surface on which the droplet is placed. For the hydrophobic surface, a nonuniform local concentration distribution exists consistently, with a high water fraction in a shell-shaped region near the liquid-air interface and a secondary concentration gradient within this shell-shaped region. The concentration distribution on the nanostructured doubly reentrant surface evolves in a more complex manner, with a strip-shaped region of high water fraction forming in the intermediate stage and then reorganized by rolling flow in the late stage. Finally, theoretical analysis combining PIV and AIE visualization results reveals that the variations in droplet concentration distributions on surfaces with different hydrophobicities exert a significant impact on evaporative behaviors. These behaviors, in turn, affect the evolution of the local concentration distribution.

Dynamics of bubble collapse near an armored free surface

Armored surfaces refer to a liquid–air interface covered by a layer of floating particles. This paper examines the collapse dynamics of a bubble generated by an electric spark near such an armored surface. The collapse of the bubble near the armored surface is similar to that near a free surface, with the formation of spraying liquid film, upward liquid jet in the forms of water dome, water spike, and water skirt with the change of the vertical distance (l) from the bubble center to the liquid surface. However, on the armored surface, we also observe particle splash and solid–liquid mixture splash. We confirm that the particle splash occurs due to the transfer of shock wave energy during bubble expansion and collapse. The splashing velocity (vp) and the distance (d0) from the bubble center to the particle follow the scaling law of vp ∼ l/d02. Additionally, we discuss the motion of the upward liquid jet and downward vortex ring. We find that the armored surface only affects the initial velocity of the jet without affecting its acceleration. This can be attributed to the additional energy dissipation caused by the splash formed on the armored surface. In contrast, the trajectory of the vortex ring remains unaffected by the armored surface. This study provides valuable insights into the dynamics of bubble collapse near an armored surface and highlights the role of floating particles in altering the behavior of liquid jets.

Wetting geometry and deposition patterns manipulation with bi-dispersed particle-laden droplets

Polygonal deposition through evaporation of the suspension droplets holds promise for printing applications. The distinctive edges present in polygonal droplets offer the potential to enhance printing resolution and enable the fabrication of diverse thin depositions. Prior investigations revolve one dimensional control with the types of wetting geometries and deposition patterns initiate from different driving factors. The current study delves into the synergistic interplay between a bi-dispersed suspension mixing ratio and particle concentration, as they collectively influence the deposition pattern of octagonal droplets formed using a micropyramid cavity patterned substrate. The investigation culminates in the development of a comprehensive phase diagram categorizing four distinct types of deposition: octagonal outer-ring deposition, octagonal ring with irregular features, octagonal uniform deposition, and central deposition. Specifically, octagonal outer-ring deposition is observed when droplets consist predominantly of 3μm particles at lower concentrations. In cases where a suspension contains 10μm particles, an intermediate concentration exceeding 50% gives a rise to the octagonal outer-ring deposition intermingled with irregular features. The octagonal uniform deposition emerges when 3μm particles, co-aggregated with 10μm particles, are compelled to settle at the deposition center within the mixture at the 3:1 ratio at 1.0 wt% and 2.6 wt%. Notably, the “curvature effect”, exhibited by the aggregates adhering to the liquid–air interface, counter-intuitively suppresses octagonal deposition despite the presence of octagonal wetting geometry and forms the central deposition. In summary, the study introduces a robust method to achieve the uniform deposition and proposes a scalable and flexible strategy for generating diverse deposition types through the judicious mixing of two suspension solutions at distinct weight ratios.

Morphology Characteristics of the Liquid–Vapour Interface in Porous Media

The evolution of the liquid–vapour interface plays a crucial role in multiphase flow, heat and mass transfer, and fluid phase change in porous media. A thorough investigation of the interface under varying degrees of saturation is necessary and crucial to fully understanding the key mechanism of soil water evaporation. The pore voids and fluids are characterized using X-ray microtomography and image processing. Salt solutions usually replace pure water for better contrast and image development. Machine learning algorithms were employed to identify and extract the different phase and their interface accurately. Then, variations in the geometrical and topological features of the interface at varying saturation during evaporation were analysed to quantitatively describe the connectivity of the liquid phase and the morphological change in the liquid–vapour interface. Topological analysis reveals that normalized Euler characteristic numbers quantify the complementary connectivity of liquid and vapour phase. The curvatures of the liquid–vapour interface of the samples under various saturations classify the liquid–air interface curvature of samples under various saturations for quantitatively describing the migration progress and quantity distribution of typical interface along with drying.