A thermally responsive PDMS composite and its microfluidic applications

This paper describes a novel composite actuator for controlled liquid actuation in microsystems which is based on a thermally responsive elastomer. The composite actuator consists of expandable microspheres incorporated in a polydimethylsiloxane (PDMS) matrix and entails the merits of both PDMS and expandable microspheres. The main characteristic of the composite actuator is to expand upon heat. The expansion is irreversible and the relative volume increase is measured up to 270% of its original volume after heating to 80 degrees C. The composite was used to fabricate single-use microfluidic pumps and valves. We show the displacement of liquids in the range of nanoliters even against counter pressures up to 100 kPa. Moreover, liquid flow in microchannels was entirely blocked by means of the integrated valves. The valves can withstand pressures up to 140 kPa. The devices are fabricated using low-cost materials only, and the composite actuator allows using wafer-level processing. The fluidic components based on the novel composite are highly integrable and do not require external actuators.