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Schematic diagram of (a) the PDMS-Glass diverging microchannel and (b) the homeotropic (normal) anchoring of the NLC molecules on the channel surfaces. In presence of flow, the molecules reorient by an angle . Plan view of the microfluidic channel indicating the diverging angle and the flow direction.
(a) POM (top row) and FCPM (middle row) micrographs of a channel filled with 5CB in absence of any flow. (b) At low flow rates, colorful birefringent domains appeared. The FCPM micrograph shows gradual decay of the signal along the downstream direction. The laser was polarized along the flow direction. (c) Snapshot during a rapidly increasing flow rate. Two distinct domains are observed. High FCPM intensity indicates strong director reorientation by the flow, compared to the weak distortion in the channel downstream. The domains are separated by a defect structure which moves downstream. The bottom row schematically represents the molecular orientation in each case. Scale bars indicate .
(a) POM micrographs showing the evolution of the birefringent domains with gradual increase of the volume flow rate as observed within the region marked in the inset (b).
Experimental (solid points) and calculated (dotted lines) values of the local flow velocity v as a function of the distance from the inlet along the channel centre for three different volume flow rates in a deep channel. The position of the different orders of the interference colors are marked on the plots. The inset shows the relation between the distortion angle , determined from the interference colors, and the local flow velocity v.
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