Application of Ferrofluid as a Valve/pump for Polycarbonate Microfluidic Devices

Integrated pumps and valves make up an essential part of most microfluidic devices and produce increased control in the device. Some existing micro-pumps and valves utilized in microfluidics involve electrical, pneumatic, and thermal actuation. However, electrical micro-pumps and valves generally entail a complicated and expensive fabrication process, and are limited to samples free of any ions or charges. We attempt to create a phase-changing pump/valve out of a mixture of ferrofluid and paraffin wax, called “ferro-wax”, that is operated by magnetic force. We utilize oil based ferrofluid solution, which is made up of magnetic iron nanoparticles and surfactant. Ferrofluid may be used as immiscible slugs that are able to separate and pump water based samples in a polycarbonate (PC) channel modified to exhibit hydrophilic properties, without leaving noticeable film. We treat different polycarbonate samples using oxygen and argon plasma, spin-on-glass (SOG), and polyvinylpyrrolidone (PVP) to find the optimal procedure to produce low contact angles with water, while maintaining high surface energy and resistance to heat. Although most of our experiments involved using ferrofluid alone, melting the ferro-wax allows it to become a fluidic pump that can be easily manipulated with an external magnet. This same procedure allows the ferro-wax to operate as a valve, by directing the fluid across a branching side channel. We work on finding the most effective ratio of ferrofluid to wax, what properties the substrate require for this pump/valve to function properly, and how to create such a microfluidic device that integrates these ferrofluid based pumps/valves.