Segmented flow of aqueous droplets transported by an immiscible separation medium in all-glass micro channels is characterized by an interplay of interface interaction and phase internal flow field formation. As a result, pressure drop, local shear rates and mixing performance are determined by this interplay. Yet, these effects are strongly influenced by the properties of the employed fluids, wettability of the channel walls and experimental conditions like flow rate and fluid phase ratio. We utilize micro Particle Imaging Velocimetry (μPIV) aside direct pressure measurements as a tool to measure and visualize these effects and show their dependency on fluidic properties and experimental conditions. All-glass micro channels have been prepared by wet etching of glass half channels and anodic bonding of two glass substrates. Micro channels have coplanar faces at top and bottom and sidewalls with a half circular shape. Wetting properties of the internal micro channel surfaces are adjusted by treatment with octadecyl-trichlorosilane. Sample droplets that fully seal the channel are embedded in a separation fluid that completely wets the channel. A permanent thin film of separation fluid prevents direct contact between sample fluid and micro channel walls. In contrast to micro channels with rectangular cross-section [1,2], we observe alternating flow circulation in separation medium and droplets under these conditions [3]. As a consequence, the total pressure drop is almost independent of droplet viscosity.

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