Elastocapillary forces have been shown to be able to induce large deformation in thin elastic structures. In case of a drop-on-fibre systems, fibres can be spooled within their liquid cavities if the capillary forces overtake the bending resistance of the fibre. These geometrical effects strongly enhance the resilience of the system seen as an elastic structure.
Here we explored the mechanical response of these hybrid systems seen as liquid drops. The production and mechanical testing are performed in a controlled microfluidic environment, all embedded onto a single chip. We produce a PDMS microfluidic chip through conventional soft photolithography that contains three zones: (I) a liquid jet production zone, (II) a fibre curing and coating area and (III) a micromechanical testing area.
After reticulation, the fibre is coated by the uncured (liquid) PEG-DA solution, allowing very good wetting conditions and ease of coiling.
The physico-chemical parameters (diameter, length and softness) of the fibres can be reliably varied, as well as the volume of the droplets carrying the fibres. The sample is then micromanipulated towards an area of the microfluidic chip with locally higher channel thickness, which allows capillary relaxation and trapping at a controlled point. The trap holds the drop as long as the drag from the external flow does not overcome the capillary forces necessary for reconfinement of the drop into the main channel.
We then compare the deformation under flow of drops and fibre-in-drop systems. We find a strong delay of the break up instability promoted by the presence of the fibre, as well as an increase in effective surface tension. These results open opportunities for a better design of liquid microcontainers and tunable microfluidic circuits with high on-off ratio for bioengineering applications.
