Analysis of photoacoustic effect of carbon nanotube- PDMS composite

Abstract

An optical ultrasound emission mechanism based on a composite of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) was investigated. Furthermore, a laser-generated ultrasound transducer which is capable of changing the center frequency using CNTs-coated polyethylene microspheres, was presented. To investigate the optical ultrasound emission mechanism, the CNTs-PDMS composite was fabricated using a brush touch method with a multi-walled carbon nanotube (MWCNT) solution mixed with CNTs and isopropyl alcohol. To explore the optical ultrasound emission mechanism, three groups of specimens were fabricated. The first group was classified as having Nd:YAG laser spot sizes when using a convex lens. The second group was classified according to the coated thickness of the CNTs. Finally, the third group was classified according to the thickness of the PDMS. The CNTs-PDMS composite was placed in a water tank, and an Nd:YAG laser was irradiated onto the CNTs-PDMS composite to receive ultrasound waves generated using a hydrophone. A comparison of the results revealed that specimens with a small laser spot size, a thick coating of CNTs, and a thin PDMS layer achieved the highest frequency of ultrasound waves.

According to these analysis, the frequency modulation of a laser-generated ultrasound transducer was conducted by the changing diameter of polymer microspheres so that the changing of laser spot size had the same effect. The ultrasound transducer is fabricated by dropping multi-walled carbon nanotubes (MWCNTs) solution, which mixed CNTs and ethoxyethanol directly on the surface of absorbing polymer microspheres. Polyethylene microspheres were selected as the absorbing polymer. The modulation of frequency depends on the diameter size of the polyethylene microspheres. To explore this relationship, three types of polyethylene microsphere with different diameters (50 μm, 100 μm, 200 μm) were used to simulate and experiment. These 3-type CNT-coated polyethylene microspheres were attached to polydimethylsiloxane (PDMS) and glass which had 1 mm thickness each. Results of comparison revealed the CNT-coated polyethylene with a diameter of 50 μm to have the highest frequency of ultrasound waves. This work shows that a smaller size absorbing polymer microsphere generate higher frequency of ultrasound waves.