In this work, we present an investigation on liquid mobility under alternate spinning on a centrifugal platform. Alternate spinning, which is defined by alternating clockwise and counterclockwise rotations, is a unique function on the centrifugal platform. It has been used to perform microfluidic functions such as mixing, and decanting to assist sample preparations. In our preliminary study, we found that the mobility of the blood plasma was very different from other aqueous solutions. In order to design a working fluidic function, it is important to understand the factors which affect the liquid mobility under alternate spinning.
The liquid mobility is quantified by the elevated volume ratio of liquids with various properties. Experimental results showed that although the liquid mobility is affected by liquid viscosity, it is consistent for the liquids with viscosities between 1 to 15 cP. (The viscosity of the blood is around 2 cP) In addition, interfacial tension and contact angle do not show prominent effect on liquid mobility. Contact angle hysteresis, which is the differences between the advancing and receding contact angles, seems to play an important role on liquid mobility under alternate spinning. The relationship between the contact angle hysteresis and the liquid mobility for various liquids and surface properties was studied and a design principle to deal with various biological fluids under alternate spinning was also presented.