In this project, we propose to visualize and measure elongation and shear stresses in low Reynolds (Re) flows of complex fluids by means of stress induced bioluminescence of microalga Gonyaulax Lingulodinium Polyedrum (LP).
Indeed, the existing stress measurement techniques are always indirect: a proxy such as strain or displacement is measured, from which stresses are subsequently interpreted. If a constitutive law between stress and strain law is lacking (which is usually the case for complex fluids) these techniques cannot be used. We strongly believe that our project will help to elaborate a direct measure of stress in any kind of complex material once bioluminescence induced by shear and extensional stress will be calibrated on a simple fluid.
Thanks to a previous financing, we now master the right conditions for growth of LP and we can control properly the biological system for doing Physics. We have characterized the motility and the coupling of motility and luminescence. We are well equipped now to continue this project as follows:
The four-roll mill device consists of a watertight and temperature-controlled internal cylindrical cell (diameter 96 mm) enclosing four rollers sets at the corners of a square. The dimensions and distance between the rollers were optimized to obtain the best approximation for homogeneous extensional flows. The rollers are turned at the same speed in opposite directions thanks to specific gearings and motors equipped with tachymeters, in order to apply an extensional flow at the center of the four roll mill. The cell is composed of a reservoir of transparent Plexiglas and stainless steel thermal control top and bottom plates, which enclose the suspension. The top and bottom parts were designed with quartz glass windows at their center, in order to observe the streamlines and the bioluminescence emitted under extensional flow at the center of the four-roll mill.
This project involves a collaboration between the LIPhy and the LRP
PI: Salima Rafaï; Post-doc: Lourdes Monica Bravo Anaya