Elongational flow of arrested complex fluid under the suppression of osmotic effective diffusion by surrounding flow of miscible solvent

Nonequilibrium interface (NI) of miscible fluids has long been of great interest; however, the acting effective interfacial tension and the deformation rate of the suspended phase in a steady immiscible state (SIS) have yet been delineated. We investigate the deformation rate and diffusion of complex fluids with a miscible surrounding fluid in a rectangular microchannel. We show here that the NI acts as a moving osmotic membrane and maintains a stable two-phase flow at a flow rate faster than the diffusion rate proportional to the osmotic pressure of the complex fluid. We report for the first time that a complex fluid suspended within a flow rate faster than the osmotic diffusion rate exhibits wet capillary thinning (WCT) behavior at the SIS. We demonstrate that either acting effective interfacial tension caused by Korteweg stress or elongational viscosity is measurable from the WCT behavior, and it was shown to be applicable to polymer solutions, animal blood, and even pure water. Our findings provide new insight into the phase behavior and managing diffusion in the flow stream of miscible fluids. The WCT technique enables precise measurement of elongational viscosity of a small amount of complex fluid, about the size of a drop without contact with the gas phase, providing a safe method for toxic, gas reactive liquid, or infected biofluids.