Flow control in microdevices using thermally responsive triblock copolymers

Active and passive microflow control has been demonstrated using gel formation by dilute aqueous solutions of triblock copolymers at elevated temperatures. Solutions of a poly(ethylene oxide)/sub 106/-poly(propylene oxide)/sub 70/-poly(ethylene oxide)/sub 106/ polymer, which has the trade name Pluronic/spl reg/ F127, have been used as a sample system. Flow in a microchannel has been stopped in less than 33 ms by introducing heat with an integrated electric heater. Viscous heating under high shear rates also induces gel formation, which has been used for passive automated flow control in a microchannel.