A latchable microvalve using phase change of paraffin wax

This paper presents a novel latchable phase-change microvalve that can potentially be used for flow gating in portable lab-on-a-chip systems where minimal energy consumption is desired. The microvalve innovatively exploits paraffin wax of low melting point, whose solid–liquid phase changes allow the closing and opening of fluid flow through deformable microchannel ceiling. The latchable phase-change actuation scheme can be used in an active valve to shut off and open fluid flow. Valve switching is initiated by melting of paraffin through heating, with an additional pneumatic pressure used for valve switching from open to closed state. Energy consumption is only required during the valve switching. After paraffin solidifies the switched state is subsequently maintained passively without further consumption of energy. The microvalve can be fabricated from PDMS through the multilayer soft lithography technique. Testing results demonstrate that the valve has response times of 60 s for closing and 100 s for opening; when closed, the valve can passively withstand a pressure up to 35 kPa without significant leakage. The relatively slow time response of the proof-of-concept device can be readily improved by integrating on-chip heaters, while the latchability of the microvalve can be improved by optimizing the wax chamber and membrane design. Compared to existing latchable phase-change valves, the thin compliant channel ceiling of the valve separates the fluid channel from the wax chamber. Therefore, the microvalve is free of potential contamination of the fluid by the paraffin wax. In addition, the improved sealing offered by the compliant membrane makes the valve robust and flexible in operation, allowing large ranges of initiation pressure generated from various actuation schemes.