A classical Mach-Zehnder interferometer is here used to measure the vapour cloud surrounding an evaporating pendant drop of 3M Novec HFE-7000 deposited on a silicon wafer with a syringe. However, in our rst experiments we observed that the droplet is highly mobile on such a perfectly at substrate, which rendered its tracking over time impossible. To make it 'stick' to a single location we use photo-litography to deposit a small object which remaines always within the droplet but still prevents the drop from moving away. This object has the shape of a disk 100 µm thick and 2 mm in diameter (noticeable in Figure S1a) made in SU-8 resin. We should stress that this protrusion has no impact on the validity of our vapour cloud measurements as it remains immersed in the drop for su ciently large drops (see Figure S1b). If it has any e ect, it will be on the recirculation inside the droplet, and even that is expected to be minor. Problems arise only for smaller drops, with a diameter approaching that of the cylindrical protrusion. As such, we decided to limit the present study to droplets larger than 2.4 mm in diameter. On the other hand, such a limitation to larger drops suited us well from the viewpoint of both a better resolution of the vapour cloud and a possible comparison with boundary-layer simulations (valid for large enough droplet sizes).

Miniature fluorescence microscopes are a standard tool in systems biology. However, widefield miniature microscopes capture only 2D information, and modifications that enable 3D capabilities increase the size and weight and have poor resolution outside a narrow depth range. Here, we achieve the 3D capability by replacing the tube lens of a conventional 2D Miniscope with an optimized multifocal phase mask at the objective’s aperture stop. Placing the phase mask at the aperture stop significantly reduces the size of the device, and varying the focal lengths enables a uniform resolution across a wide depth range. The phase mask encodes the 3D fluorescence intensity into a single 2D measurement, and the 3D volume is recovered by solving a sparsity-constrained inverse problem. We provide methods for designing and fabricating the phase mask and an efficient forward model that accounts for the field-varying aberrations in miniature objectives. We demonstrate a prototype that is 17 mm tall and weighs 2.5 grams, achieving 2.76 μm lateral, and 15 μm axial resolution across most of the 900 × 700 × 390 μm3 volume at 40 volumes per second. The performance is validated experimentally on resolution targets, dynamic biological samples, and mouse brain tissue. Compared with existing miniature single-shot volume-capture implementations, our system is smaller and lighter and achieves a more than 2× better lateral and axial resolution throughout a 10× larger usable depth range. Our microscope design provides single-shot 3D imaging for applications where a compact platform matters, such as volumetric neural imaging in freely moving animals and 3D motion studies of dynamic samples in incubators and lab-on-a-chip devices.

Freely receding evaporating sessile droplets of perfectly wetting liquids, for which the observed finite contact angles are attributed to evaporation, are studied with a Mach-Zehnder interferometer. The experimentally obtained droplet shapes are found to depart, under some conditions, from the classical macroscopic static profile of a sessile droplet. The observed deviations (or the absence thereof) are explained in terms of a Marangoni flow due to evaporation-induced thermal gradients along the liquid-air interface. When such a Marangoni effect is strong, the experimental profiles exhibit a maximum of the slope at a certain distance from the contact line. In this case, the axisymmetric flow is directed from the contact line to the apex (along the liquid-air interface), hence delivering more liquid to the center of the droplet and making it appear inflated. These findings are quantitatively confirmed by predictions of a lubrication model accounting for the impact of the Marangoni effect on the droplet shape.

-We here show how evaporation/condensation processes lead to efficient heat spreading along a liquid/gas interface, thereby damping thermal fluctuations and hindering thermocapillary flows. This mechanism acts as an effective thermal conductivity of the gas phase, which is shown to diverge when the latter is made of pure vapor. Our simple (fitting-parameter-free) theory nicely agrees with measurements of critical conditions for Bénard-Marangoni instability in drying liquid films. Heat spreading is also shown to strongly affect wavelength selection in the nonlinear regime. In addition to providing a quantitative framework for analyzing transitions between complex evaporation-driven patterns, this also opens new perspectives for better controlling deposition techniques based on drying.

No abstract

Mach-Zehnder interferometry was applied to explore the effects of inhomogeneous magnetic fields on the mobility of rare-earth ions in aqueous solutions. No migration of ions was observed in a thermodynamically closed system when a homogeneous solution was subjected to a magnetic field gradient alone. However, magnetomigration could be triggered by a concentration gradient of the rare-earth ions in the solution. When a concentration gradient was introduced in the sample by solvent evaporation, consistent migration of paramagnetic Dy ions from the bulk solution to regions with stronger magnetic fields was observed. By contrast, no movement was detected for diamagnetic Y ions in the presence of a concentration gradient.

A lot of chemical engineering processes are based on chemical reactions between a gas and a component in a liquid phase. The gas has to be dissolved in the liquid phase. It is commonly admitted that the global gas-liquid mass transfer rate is controlled by phenomena occurring in layers close to the gas-liquid interface (mainly diffusion, but also convection and reactions). Therefore, a good understanding of these phenomena is required to achieve an optimization of the processes. This work deals with the development of a new experimental tool and an original procedure to study phenomena occurring during gas-liquid absorption coupled with chemical reactions in the liquid phase. The digital holographic interferometry is used to visualize the formation and the development of the diffusion boundary layer of the transferred mass in the liquid phase close to the gas-liquid interface. The gas-liquid mass absorption is realized inside a Hele-Shaw cell and a Mach-Zehnder interferometer is used to visualize the phenomena occurring in the liquid phase during this transfer. A procedure is developed to estimate the physico-chemical parameters (solubility, diffusion coefficient, kinetic constant, …) of a mass transfer model, coupling diffusion and chemical reactions, in the liquid of the Hele-Shaw cell. On the one hand, an image processing program is developed to extract quantitative information from the raw experimental results. On the other hand, a parametric estimation method, which is based on a non-linear least-square fitting, is developed to estimate the physico-chemical parameters of this mass transfer model from the experimental results. The presented method is used to study the gaseous CO2 absorption in NaHCO3-Na2CO3 aqueous solution. A mass transfer model, coupling diffusion and chemical reactions, in the liquid of the Hele-Shaw cell, is presented and solved numerically by a finite element method using the COMSOL Multiphysics software. A set of CO2 absorption experiments, using several couples of NaHCO3-Na2CO3 initial concentrations, is realized. The physico-chemicals parameters of the mass transfer model are estimated for some experiments. The obtained values are compared to the value calculated from correlations found in the literature. Using the estimated parameter values, a good agreement between the experimental and the simulated evolutions of the diffusion boundary layer is obtained. These results tend to validate the proposed procedure.

A novel measuring technique for bubbly flows, named Glare Point Velocimetry and Sizing (GPVS), was developed in order to measure both bubble size and velocity with a high accuracy in a 2D plane. This is accomplished by observing glare points in-focus under an observation angle of 96• . When a second laser-sheet is added, even higher accuracies are obtained and the relative refractive index of the bubble can be measured. It also allows non-spherical bubbles to be rejected and arbitrary angles to be used (e.g. 90• ). The accuracy of the size and refractive index measurements was found to be within 1,3%.