Thermo-actuated migration in microsystems

This project is done in the framework of the ANR project TRAM. Our partners are IPR-Rennes, LIONS-CEA, LAI-Marseilles and IDA-Jussieu. 
Foam Drainage Control Using Thermocapillary Stress in a Two-Dimensional Microchamber

PhD thesis of Vincent Miralles

in collaboration with Isabelle Cantat IPR-Rennes

We investigate the drainage of a 2D microfoam in a vertical Hele-Shaw cell, and show that the Marangoni stress at the air-water interface generated by a constant temperature gradient applied in situ can be tuned to control the drainage. The temperature gradient is applied in such a way that thermocapillarity and gravity have an antagonistic effect. We characterize the drainage over time by measuring the liquid volume fraction in the cell and find that thermocapillarity can overcome the effect of gravity, effectively draining the foam towards the top of the cell, or exactly compensate it, maintaining the liquid fraction at its initial value over at least 60 s.We quantify these results by solving the mass balance in the cell, and provide insight into the interplay between gravity, thermocapillarity, and capillary pressure governing the drainage dynamics.

The figure aside represents the time evolution of the liquid fraction for varying the applied temperature gradient. At a critical temperature gradient, the gravitational drainage is stopped.

Miralles et al., Phys. Rev. Lett. 2014

Investigating the role of a poorly soluble surfactant in a thermally driven 2D microfoam 

PhD thesis of Vincent Miralles

in collaboration with Isabelle Cantat IPR-Rennes, E. Rio LPS-Orsay

The foam drainage dynamics is known to be strongly affected by the nature of the surfactants stabilising the liquid/gas interface. In the present work, we consider a 2D microfoam stabilized by both soluble (sodium dodecylsulfate) and poorly soluble (dodecanol) surfactants. The drainage dynamics is driven by a thermocapillary Marangoni stress at the liquid/gas interface and the presence of dodecanol at the interface induces interface stress acting against the applied thermocapillary stress, which slows down the drainage dynamics. We define a damping parameter that we measure as a function of the geometrical characteristics of the foam. We compare it with predictions based on the interface rheological properties of the solution.

Miralles et al., Soft Matter 2016

A versatile technology for droplet-based microfluidics: thermomechanical actuation

PhD thesis of Margaux Kerdraon

PhD thesis of Vincent Miralles and Axel Huerre, internships of Hannah Williams and Bastien Fournié

We report on a versatile technique for microfluidic droplet manipulation that proves effective at every step: from droplet generation to propulsion to sorting, rearrangement or break-up. Non-wetting droplets are thermomechanically actuated in a microfluidic chip using local heating resistors. Controlled temperature variation induces local dilation of the PDMS wall above the resistor, which drives the droplet away from the hot (i.e. constricted) region (B. Selva, I. Cantat and M.-C. Jullien, Phys. Fluids, 2011, 23, 052002). Adapted placing and actuation of such resistors thus allow us to push forward, stop, store and release, or even break up droplets, at the price of low electric power consumption (<150 mW). We believe this technically accessible method to provide a useful tool for droplet microfluidics.

Miralles et al., Lab Chip, 2015

Liquid fraction for different temperature gradients.

Damping factor r as a function of the DOH bulk concentration

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