High-speed photoacoustic laser streaming and on-demand fluid mixing in a microfluidic chip with carbon nanotube-based elastomers.

Carbon nanotube (CNT)-based elastomers are renowned for generating high acoustic pressures via the photoacoustic effect, while little photoacoustic laser streaming (PALS) has been observed. In this work, we overcome this challenge by identifying laser spot diameter and repetition rate as two most important parameters governing PALS with CNT-polydimethylsiloxane (CNT-PDMS) composite elastomers. When a nanosecond laser with the repetition rate of 2000 Hz was focused to a 200 µm spot, we achieved a record-high PALS velocity of 28.1 cm/s. This soft, low-cost photoacoustic elastomer can mix two fluids within one minute in a milliliter-scale container, and it allows on-demand mixing of two laminar flows simply by switching on the laser without the need for microelectromechanical structures integrated into microfluidic channels. The high-speed PALS and controllable microfluidic mixing, established CNT composite elastomer as an excellent PALS medium and opens up new possibilities for practical photoacoustic microfluidics.