An optopneumatic piston for microfluidics.

We demonstrate an optopneumatic piston based on glass capillaries, a mixture of PDMS-carbon nanopowder, silicone and mineral oil. The fabrication method is based on wire coating techniques and surface tension-driven instabilities, and allows for the assembly of several pistons from a single batch production. By coupling the photothermal response of the PDMS-carbon mixture with optical excitation via an optical fiber, we demonstrate that the piston can work either as a valve or as a reciprocal actuator. The death volume of the pistons was between 0.02 and 1.56 μL and the maximum working frequency was around 1 Hz. Analysis of the motion during the expansion/contraction of the piston shows that this machine can be described by a phenomenological equation analogous to the Kelvin-Voight model used in viscoelasticity, having elastic and viscous components.