Flow-induced switching between blue phases

Blue-phases (BPs) are highly ordered soft materials that appear in a narrow temperature range between the chiral nematic and the isotropic phases. BPs exhibit cubic arrangements of double-twist cylinders and disclination lines with characteristic length scales of the wavelength of visible light. Between BPI and BPII exist topological differences which are significantly responsible for their different dynamical response under external stimuli. Here we focus on the dynamic and out-of-equilibrium states of BPII under shear stresses in pressure-driven flow inside microfluidic channels. We show in experiments how precise tuning of the driving pressure on BPII with the lattice orientation (111) can be used to stabilize and manipulate a previously unresearched switching state between BPII and BPI. Combining experiments with simulations, we try to understand the dynamics of disclinations lines and how they are affected by hydrodynamic forces. We also characterize the sequence of all dynamical, flow-induced out-of-equilibrium regimes when subject to a pressure-driven flow in a microfluidic geometry with controlled anchoring conditions.