A Low-Voltage Microfluidic Valve Based upon a Reversible Hydrophobicity Effect

A microfluidic valve is reported based on a reversible hydrophobicity effect via the growth and retraction of nanotextured metal filaments on the surface of a solid electrolyte. The valve is integrated onto the bottom of the channel and actuated by a DC voltage. The dendritic silver filaments are tens to hundreds of nanometers in height and can be isolated from the channel fluid by a thin Parylene layer. An applied bias of 6 V or less grows or dissolves the filaments, depending on the polarity, and the roughness so created alters the fluid-surface interface, manipulating hydrophobicity of the interface, transitioning from the lotus effect to the petal effect. To demonstrate this valve, the fluid flow in a poly(dimethylsiloxane)-enclosed microfluidic channel of up to 30 μm in depth and up to 250 μm in width is stopped and restarted within ≈25 s of actuation. The effect is nonvolatile, thus no static power is required to retain the on/off states of the valve.