Manipulation of Elastic Instability of Viscoelastic Fluid in a Rhombus Cross Microchannel.

This paper reports the manipulation of elastic instability of the viscoelastic fluid in a rhombus cross microchannel (RCM) structure. The bistable instability and unsteady instability of the flow is firstly demonstrated in a standard cross microchannel (SCM) for reference. We then keep the bi-stable instability over a much wider injection rate range in the RCM, which is attributed to the stabilizing effect of the rhombus structure. A semi-bistable instability was also established in the RCM at a high enough injection rate. In addition, the unsteady elastic instability is realized in the RCM through an asymmetric injection rate condition.

Flow Direction-Dependent Elastic Instability in a Symmetry-Breaking Microchannel.

This paper reports flow direction-dependent elastic instability in a symmetry-breaking microchannel. The microchannel consisted of a square chamber and a nozzle structure. A viscoelastic polyacrylamide solution was used for the instability demonstration. The instability was realized as the viscoelastic flow became asymmetric and unsteady in the microchannel when the flow exceeded a critical Weissenberg number. The critical Weissenberg number was found to be different for the forward-directed flow and the backward-directed flow in the microchannel.

Microfluid-based soft metasurface for tunable optical activity in THz wave.

Metasurfaces are usually planar structures and do not possess intrinsic chirality and therefore hardly generate optical activity. Here we realized a tunable optical activity in a terahertz wave through a microfluid-based soft metasurface. The meta-atom is a chiral structured microchannel made of soft polydimethylsiloxane and injected with the liquid metal Galinstan. A microfluid pressure system is bonded to the metasurface to reconfigure all meta-atoms simultaneously. By pumping glycerol liquid into the pressure system, the metasurface is deformed from a planar structure to a three dimensional one, which manifests intrinsic chirality for optical activity realization. By controlling the injected glycerol volume, a polarization rotation from 0°to 14° at 0.19 THz is demonstrated. The soft metasurface with tunable optical activity can be flexibly applied in various applications such as polarization microscopy, bio-detection and material analysis, etc.