Beng Hau Tan

Phenomena in diverse contexts such as wetting, biological assembly, and manufacturing are attributed to the three-phase line tension. However, decades of line tension estimates based on contact angles of droplets controversially span 6 orders of magnitude, raising the question of which measurements are authoritative. Here, we show with experiments and calculations that contact angles fail to estimate line tension regardless of length scale, technique, and measurement quality. Line tension measurements based on contact angles are driven by two distinct and spurious mechanisms: body forces under ideal conditions, and data scatter under noisy conditions.

The line tension of a three-phase contact line is implicated in a wide variety of interfacial phenomena, but there is ongoing controversy, with existing measurements spanning six orders of magnitude in both signs. Here, we show that computationally obtained magnitudes, sign changes, and nontrivial variations of apparent line tension can be faithfully reproduced in a parsimonious model that incorporates only liquid-substrate interactions. Our results suggest that the origin for the remarkable variation lies in the failure of a widely used estimation method to eliminate body forces, leading measured line tensions to behave like an extensive quantity.

DOI: https://doi.org/10.1103/PhysRevLett.129.099601

Solvent exchange facilitates high-density nucleation of sessile nanodroplets or nanobubbles by successively wetting a surface with two solvents of contrasting solubility with respect to a target species. Yet the key physical mechanisms underlying its efficacy have yet to be theoretically explained. We develop a minimal model for solvent exchange, for the prototypical example of water and ethanol as the solvents and nitrogen as the target species. Our calculations show that solvent exchange is mediated by transient solubility gradients that dominate over the intrinsic concentration gradient of nitrogen in the incipient moments after exchange. Solubility gradients advect nitrogen toward the substrate during ethanol-water exchange but away from it in water-ethanol exchange, consistent with the directionality observed in experiments.

Nanoblisters have attracted attention due to their ability to controllably modulate the properties of two-dimensional materials. The accurate measurement or estimation of their properties is non-trivial and largely based on Hencky’s theory. However, these estimates require a priori knowledge of material properties and propagate large errors. Here we show through a systematic atomic force microscopy study, several strategies that lead to vastly enhanced characterisation of nanoblisters. First, we find that nanoblisters may contain both liquid and gas, resolving an ongoing debate in the literature. Second, we demonstrate how to definitively determine the membrane thickness of a nanoblister, and show that Hencky’s theory can only reliably predict membrane thicknesses for small aspect ratios and small membrane thicknesses. Third, we develop a novel technique to measure the internal pressures of nanoblisters, which quantitatively agrees with Hencky’s theory but carries a one order smaller propagated error.

The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study, the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot, the rapid merging of the two liquid films proceeds. Thereby, the connecting rim is rapidly accelerated into the separating gas layer. We show that, due to the dimple formation, the velocity is not uniform and the high acceleration initially causes a Rayleigh–Taylor instability of the liquid rim. At later times, the rim heals and takes on a circular shape. However, for sufficiently high concentrations of the surfactant, the unstable rim pinches off microbubbles, resulting in a fractal dendritic structure after coalescence.The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study, the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot, the rapid merging of the two liquid films proceeds. Thereby, the connecting rim is rapidly accelerated into the separating gas layer. We show that, due to the dimple formation, the velocity is not uniform and the high acceleration initially causes a Rayleigh–Taylor instability of the liquid rim. At later times, the rim heals and takes on a circular shape. However, for sufficiently high concentrations of the surfactant, the unstable rim pinches off microbubbles, resulting in a fractal dendritic structure after coalescence.

The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study, the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot, the rapid merging of the two liquid films proceeds. Thereby, the connecting rim is rapidly accelerated into the separating gas layer. We show that, due to the dimple formation, the velocity is not uniform and the high acceleration initially causes a Rayleigh–Taylor instability of the liquid rim. At later times, the rim heals and takes on a circular shape. However, for sufficiently high concentrations of the surfactant, the unstable rim pinches off microbubbles, resulting in a fractal dendritic structure after coalescence.The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study, the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot, the rapid merging of the two liquid films proceeds. Thereby, the connecting rim is rapidly accelerated into the separating gas layer. We show that, due to the dimple formation, the velocity is not uniform and the high acceleration initially causes a Rayleigh–Taylor instability of the liquid rim. At later times, the rim heals and takes on a circular shape. However, for sufficiently high concentrations of the surfactant, the unstable rim pinches off microbubbles, resulting in a fractal dendritic structure after coalescence.

The merging of two soap bubbles is a fundamental fluid mechanical process in foam formation. In the present experimental study, the liquid films from two soap bubbles are brought together. Once the liquid layers initially separated by a gas sheet are bridged on a single spot, the rapid merging of the two liquid films proceeds. Thereby, the connecting rim is rapidly accelerated into the separating gas layer. We show that, due to the dimple formation, the velocity is not uniform and the high acceleration initially causes a Rayleigh–Taylor instability of the liquid rim. At later times, the rim heals and takes on a circular shape. However, for sufficiently high concentrations of the surfactant, the unstable rim pinches off microbubbles, resulting in a fractal dendritic structure after coalescence.