Capillary Rise of Yield Stress Fluids

Cell & DNA solutions, blood, food, cosmetics, and polymer mixtures are examples of yield stress fluids (YSFs). They frequently wet narrow channels, as seen in a blood test for virus and a recovery of crude oil. In this talk, we present the capillary rise of various YSFs in vertical glass capillaries, and find a unique rise curve distinct from Newtonian fluids; the rise slows down to a plateau in the middle, followed by the sudden increase to the final equilibrium. We show that this plateau is originated from a competition between Laplace pressure and the yield stress. Furthermore, it is also found that the second rise from the plateau greatly depends on a liquid-solid transition speed or 'yielding rate'.