taksc

• Zheng, Boxue; Chan, Tak Shing; Brummelen, Harald Van & Snoeijer, Jacco H. (2025). Dynamics of poro-viscoelastic wetting with large swelling. Journal of Fluid Mechanics. ISSN 0022-1120. 1025(A58). doi: 10.1017/jfm.2025.10977. Full text in Research Archive Show summary

  The deposition of droplets onto a swollen polymer network induces the formation of a wetting ridge at the contact line. Current models typically consider either viscoelastic effects or poroelastic effects, while polymeric gels often exhibit both properties. In this study, we investigate the growth of the wetting ridge using a comprehensive large-deformation theory that integrates both dissipative mechanisms – viscoelasticity and poroelasticity. In the purely poroelastic case, following an initial instantaneous incompressible deformation, the growth dynamics exhibits scale-free behaviour, independent of the elastocapillary length or system size. A boundary layer of solvent imbibition between the solid surface (in contact with the reservoir) and the region of minimal chemical potential is created. At later times, the ridge equilibrates on the diffusion time scale given by the elastocapillary length. When viscoelastic properties are incorporated, our findings show that, during the early stages (prior to the viscoelastic relaxation time scale), viscoelastic effects dominate the growth dynamics of the ridge and solvent transport is significantly suppressed. Beyond the relaxation time, the late-time dynamics closely resembles that of the purely poroelastic case. These findings are discussed in light of recent experiments, showing how our approach offers a new interpretation framework for wetting of polymer networks of increasing complexity.

• Zheng, Boxue & Chan, Tak Shing (2025). Soft Wetting Ridge Rotation in Sessile Droplets and Capillary Bridges. Langmuir. ISSN 0743-7463. 41(6). doi: 10.1021/acs.langmuir.4c04667. Full text in Research Archive Show summary

  We investigate the deformation of soft solid layers in the presence of sessile droplets or capillary bridges. Unlike models that assume Young’s law governs the contact angle, we incorporate the surface tension balance at the contact line to analyze the rotation of the wetting ridge and the corresponding change in the contact angle. Our findings reveal that the rotation direction of the wetting ridge aligns with the sign of the Laplace pressure. Interestingly, although a softer solid layer typically decreases the contact angle for sessile droplets, a negative Laplace pressure in a hydrophilic capillary bridge pulls the solid–liquid interface, leading to an increased contact angle. A hydrophilic capillary bridge would be expected to move from thicker regions of a soft layer to thinner areas, exhibiting behavior opposite that of a sessile droplet. The interplay between soft layer deformation and contact angle modulation provides valuable insights into controlling droplet motion through elastocapillarity.

• Bharti, Bharti; Carlson, Andreas & Chan, Tak Shing (2024). Plateau-Rayleigh instability of a soft layer coated on a rigid cylinder. Soft Matter. ISSN 1744-683X. 20(27), p. 5456–5463. doi: 10.1039/d4sm00061g. Full text in Research Archive Show summary

  We study the Plateau–Rayleigh instability of a soft viscoelastic solid layer coated on a rigid cylinder i.e., a soft fibre with a rigid core. The onset of instability is examined using a linear stability analysis. We find that increasing the rigid cylinder radius or the stiffness of the layer reduces the growth rate of the fastest growing mode. For each rigid cylinder radius, a critical elastocapillary number is found below which all wavelengths of disturbances are stable. The critical value for a soft fibre with a thick rigid cylindrical core can be several orders of magnitudes larger than that for a totally soft fibre (no rigid core). This highlights the strong stabilizing effect of the rigid core on the system. Increasing the relaxation timescale of the viscoelastic material also slows down the growth of disturbances, but has no effect on the critical elastocapillary number. Interestingly, the wavelength of the fastest growing mode is independent of the rigid cylinder radius for the purely elastic case.

• Bharti, Bharti; Carlson, Andreas; Chan, Tak Shing & Salez, Thomas (2024). Plateau-Rayleigh instability of a viscous film on a soft fiber. Europhysics letters. ISSN 0295-5075. 145(6). doi: 10.1209/0295-5075/ad2e77. Full text in Research Archive
• Bharti, Bharti; Ferreira, Quentin; Jha, Aditya; Carlson, Andreas; Dean, David S. & Amarouchene, Yacine [Show all 8 contributors for this article] (2024). Singular viscoelastic perturbation to soft lubrication. Physical Review Research (PRResearch). 6(4). doi: 10.1103/PhysRevResearch.6.043060. Full text in Research Archive Show summary

  Soft lubrication has been shown to drastically affect the mobility of an object immersed in a viscous fluid in the vicinity of a purely elastic wall. In this theoretical article, we develop a minimal model incorporating viscoelasticity, carrying out a perturbation analysis in both the elastic deformation of the wall and its viscous damping. Our approach reveals the singular-perturbation nature of viscoelasticity to soft lubrication. Numerical resolution of the resulting nonlinear, singular, and coupled equations of motion reveals peculiar effects of viscoelasticity on confined colloidal mobility, opening the way towards the description of complex migration scenarios near realistic polymeric substrates and biological membranes.

• Zheng, Boxue; cai, zhiwen; zhao, peidong; xu, xiaoyang; Chan, Tak Shing & peng, yu (2024). A generalized density dissipation for weakly compressible smoothed particle hydrodynamics. Physics of Fluids. ISSN 1070-6631. 36(8). doi: 10.1063/5.0216702. Full text in Research Archive Show summary

  Weakly compressible smoothed particle hydrodynamics (SPH) is known to suffer from numerical pressure noise, posing challenges to simulation stability and accuracy. To address this, the present study introduces a novel density dissipation scheme aimed at suppressing such unphysical noise. The proposed solution overcomes the limitation of traditional density dissipation schemes being ineffective at fluid interfaces in multiphase flow simulations. The novel scheme is generally applicable to the entire computational domain, encompassing both single-phase flow and multiphase flow. This advancement is achieved through two key components. First, the traditional density dissipation is replaced with a density increment dissipation approach that enables dissipation to cross interfaces separating different fluids. Second, based on dissipation volume conservation, a dissipation volume correction factor is employed to stabilize simulations characterized by large density ratios. The accuracy, stability, and robustness of our method are demonstrated through direct comparisons with experimental data or numerical results in four three-dimensional benchmarks: sloshing under external excitations, the rising of single and double bubbles, Rayleigh–Taylor instability, and Kelvin–Helmholtz instability. Additionally, our study reveals the relationship between SPH utilizing density dissipation and the approximate Riemann solver.

• Zheng, Boxue; Pedersen, Christian; Carlson, Andreas & Chan, Tak Shing (2023). Static wetting of a barrel-shaped droplet on a soft-layer-coated fiber. Soft Matter. ISSN 1744-683X. 19(46), p. 8988–8996. doi: 10.1039/d3sm00951c. Full text in Research Archive Show summary

  A droplet can deform a soft substrate due to capillary forces when they are in contact. We study the static deformation of a soft solid layer coated on a rigid cylindrical fiber when an axisymmetric barrel-shaped droplet is embracing it. We found that elastic deformation increases with a decreasing rigid fiber radius. Significant disparities of deformation between the solid–liquid side and the solid–gas side are found when their solid surface tensions are different. When the coated layer is soft enough and the rigid fiber radius is less than the thickness of the coated layer, pronounced displacement oscillations are observed. Such slow decay of deformation with distances from the contact line position suggests a possible long-range interaction between droplets on a soft-layer-coated fiber.

• Chan, Tak Shing (2022). The growth and the decay of a visco-elastocapillary ridge by localized forces. Soft Matter. ISSN 1744-683X. 38(18), p. 7280–7290. doi: 10.1039/d2sm00913g. Full text in Research Archive Show summary

  A soft solid layer develops a ridge-like deformation below the contact line due to the pulling force of the liquid–air surface tension when a droplet is in contact with it. We investigate the growth and the decay of a viscoelastic wetting ridge. The global features, e.g. the ridge height, evolve with time scales corresponding to the relaxation of the viscoelastic material. In contrast, we show that locally around the tip of the ridge, the surface tensions not only determine the equilibrium shape, but also have a significant impact on the dynamics, for which the relaxation has a characteristic spreading velocity depending on the solid surface tension. The relaxation time to an equilibrium state depends on the distance from the contact line, which can be much smaller than the long-term relaxation time scale of the viscoelastic material. The different dynamics between the global features of the ridge and the tip morphology suggests an alternative focus when investigating the contact line dynamics in soft wetting, such as stick-slip motion.

• Lee, Carmen L.; Chan, Tak Shing; Carlson, Andreas & Dalnoki-Veress, Kari (2022). Multiple droplets on a conical fiber: formation, motion, and droplet mergers. Soft Matter. ISSN 1744-683X. 18(7), p. 1364–1370. doi: 10.1039/d1sm01462e. Full text in Research Archive
• Chan, Tak Shing; Lee, Carmen L.; Pedersen, Christian; Dalnoki-Veress, Kari & Carlson, Andreas (2021). Film coating by directional droplet spreading on fibers. Physical Review Fluids. 6(1). doi: 10.1103/PhysRevFluids.6.014004. Full text in Research Archive Show summary

  Plants and insects use slender conical structures to transport and collect small droplets, which are propelled along the conical structures due to capillary action. These droplets can deposit a fluid film during their motion, but despite its importance to many biological systems and industrial applications, the properties of the deposited film are unknown. We characterize the film deposition by developing an asymptotic analysis together with experimental measurements and numerical simulations based on the lubrication equation. We show that the deposited film thickness depends significantly on both the fiber radius and the droplet size, highlighting that the coating is affected by finite-size effects relevant to film deposition on fibers of any slender geometry. We demonstrate that by changing the droplet size, while the mean fiber radius and the capillary number are fixed, the thickness of the deposited film can change by an order of magnitude or more. We show that self-propelled droplets have significant potential to create passively coated structures.

• Chan, Tak Shing; Kamal, Catherine; Snoeijer, Jacco H.; Sprittles, James E. & Eggers, Jens (2020). Cox–Voinov theory with slip. Journal of Fluid Mechanics. ISSN 0022-1120. 900(A8). doi: 10.1017/jfm.2020.499. Full text in Research Archive Show summary

  Most of our understanding of moving contact lines relies on the limit of small capillary number Ca . This means the contact line speed is small compared to the capillary speed γ/η , where γ is the surface tension and η the viscosity, so that the interface is only weakly curved. The majority of recent analytical work has assumed in addition that the angle between the free surface and the substrate is also small, so that lubrication theory can be used. Here, we calculate the shape of the interface near a slip surface for arbitrary angles, and for two phases of arbitrary viscosities, thereby removing a key restriction in being able to apply small capillary number theory. Comparing with full numerical simulations of the viscous flow equation, we show that the resulting theory provides an accurate description up to Ca≈0.1 in the dip coating geometry, and a major improvement over theories proposed previously.

• Chan, Tak Shing; Pedersen, Christian; Koplik, Joel & Carlson, Andreas (2020). Film deposition and dynamics of a self-propelled wetting droplet on a conical fibre. Journal of Fluid Mechanics. ISSN 0022-1120. 907, A29, p. 907 A29-1–907 A29-22. doi: 10.1017/jfm.2020.834. Full text in Research Archive Show summary

  We study the dynamic wetting of a self-propelled viscous droplet using the time-dependent lubrication equation on a conical-shaped substrate for different cone radii, cone angles and slip lengths. The droplet velocity is found to increase with the cone angle and the slip length, but decrease with the cone radius. We show that a film is formed at the receding part of the droplet, much like the classical Landau–Levich–Derjaguin film. The film thickness hf is found to decrease with the slip length λ. By using the approach of matching asymptotic profiles in the film region and the quasi-static droplet, we obtain the same film thickness as the results from the lubrication approach for all slip lengths. We identify two scaling laws for the asymptotic regimes: hfh′′o∼Ca2/3 for λ≪hf and hfh′′3o∼(Ca/λ)2 for λ≫hf; here, 1/h′′o is a characteristic length at the receding contact line and Ca is the capillary number. We compare the position and the shape of the droplet predicted from our continuum theory with molecular dynamics simulations, which are in close agreement. Our results show that manipulating the droplet size, the cone angle and the slip length provides different schemes for guiding droplet motion and coating the substrate with a film.

• Chan, Tak Shing; Yang, Fan & Carlson, Andreas (2020). Directional spreading of a viscous droplet on a conical fibre. Journal of Fluid Mechanics. ISSN 0022-1120. 894(A26). doi: 10.1017/jfm.2020.240. Full text in Research Archive Show summary

  If a droplet smaller than the capillary length is placed on a substrate with a conical shape, it spreads by itself in the direction of growing fibre radius. We describe this capillary spreading dynamics by developing a lubrication flow approximation on a cone and by using the perturbation method of matched asymptotic expansions. Our results show that the droplet appears to adopt a quasi-static shape and the predictions of the droplet shape and the spreading velocity from the two mathematical models are in excellent agreement. At the contact line regions, a large pressure gradient is generated by the mismatch between the equilibrium contact angle and the apparent contact angle that maintains the viscous flow. It is the conical shape of the substrate that breaks the front/rear droplet symmetry in terms of the apparent contact angle, which is larger at the thicker part of the cone than at its thinner part. Consequently, the droplet is predicted to move from the cone tip to its base, consistent with experimental observations.

• Chan, Tak Shing & Carlson, Andreas (2019). Physics of adhesive organs in animals. The European Physical Journal Special Topics (EPJ - Special Topics (EPJ ST)). ISSN 1951-6355. 227(17), p. 2501–2512. doi: 10.1140/epjst/e2019-800131-2. Full text in Research Archive

View all works in NVA

• Chan, Tak Shing (2025). Wetting on soft solids. Full text in Research Archive
• Chan, Tak Shing (2025). Wetting on soft solids. Full text in Research Archive
• Zheng, Boxue; Chan, Tak Shing; Brummelen, Harald van & Snoeijer, Jacco H. (2024). Title Capillary-Induced Deformation and Solvent Transport in Hydrogels. Full text in Research Archive
• Zheng, Boxue; Chan, Tak Shing; Brummelen, Harald van & Snoeijer, Jacco H. (2024). Capillary-Induced Deformation and Solvent Transport in Hydrogels. Full text in Research Archive
• Zheng, Boxue; Pedersen, Christian; Carlson, Andreas & Chan, Tak Shing (2023). Static wetting of a droplet on a soft-layer-coated fiber. Full text in Research Archive
• Zheng, Boxue; Pedersen, Christian; Carlson, Andreas & Chan, Tak Shing (2023). Static wetting of a droplet on a soft-layer-coated fiber. Full text in Research Archive
• Zheng, Boxue; Pedersen, Christian; Carlson, Andreas & Chan, Tak Shing (2023). Static wetting of a barrel-shaped droplet on a soft-layer-coated fiber. Full text in Research Archive
• Chan, Tak Shing & Zheng, Boxue (2023). Capillary bridges between partially wetting soft substrates. Full text in Research Archive
• Zheng, Boxue; Pedersen, Christian; Carlson, Andreas & Chan, Tak Shing (2023). Static wetting of a droplet embracing a fiber coated with a soft layer. Full text in Research Archive
• Bharti, Bharti; Chan, Tak Shing & Carlson, Andreas (2023). Plateau-Rayleigh Instability of a Viscous Film on a Soft Fiber. Full text in Research Archive
• Bharti, Bharti; Carlson, Andreas & Chan, Tak Shing (2023). Plateau-Rayleigh Instability of a Soft Viscoelastic Cylinder with a Rigid Inner Core. Full text in Research Archive
• Bharti, Bharti; Carlson, Andreas & Chan, Tak Shing (2023). Plateau-Rayleigh Instability of a Soft Viscoelastic Cylinder with a Rigid Inner Core. Full text in Research Archive
• Chan, Tak Shing (2023). Stability of surface nanobubbles on a rigid/soft solid substrate. Full text in Research Archive
• Chan, Tak Shing (2023). Static wetting of a droplet on a soft-layer-coated fiber. Full text in Research Archive

View all works in NVA