Reversible Thermally-Responsive Copolymer Valve for Manipulating Water Wicking

Wicking action produced equipment is widely noted for its ease of miniaturization, simplicity of equipment, and lack of external energy supply requirement. However, current materials used for controlled wicking are very scarce and not reversible, severely limiting the application of the wicking phenomenon. In this work, a reversible thermally responsive valve is developed from thermally responsive copolymer [poly( N -acryloyl glycinamide-co-styrene), PNAGA/PSt], which shows suitable temperature-dependent wicking performance. The wicking capacity of the valve can be increased by 5.75 times from 20 to 80 °C and can be cycled at least five times. The excellent wicking performance is ascribed to the hydrogen bonding variation of PNAGA/PSt. The wicking is controlled by temperature only. Furthermore, based on the thermally responsive valve, a microflow platform is developed to promote or prevent large drop (45 μL) accumulation. This work opens a new avenue to design and prepare materials with controlled wicking capability, providing a platform for water collection, miniature biochemical reactions, and microliquid control.