Performance of a photothermal actuator based on molecular absorbers dissolved in eicosane

Photothermal wax motors provide a way to directly transform photon energy into mechanical work. To provide a simple testbed for assessing their performance, a cylindrical wax motor actuator was fabricated that allows direct light access from one end and has a deformable silicone membrane on the other end. Eicosane (C20H42) was used as the phase change material, with guaiazulene (GAZ) and Lumogen Orange F 240 (LO) as the absorber molecules. This actuator was tested under a variety of experimental conditions, including resistive versus light-mediated heating, absorber identity and concentration, and filling. The GAZ/eicosane actuator could reach full extension after 137 s under 2 W of incident 532 nm laser light and undergo 100 cycles without loss of function. Both theory and experiment show that the absorber concentration influences the dynamic response of the actuator. The ability of the perylenediimide dye LO to generate a photothermal expansion suggests that highly luminescent and photostable chromophores can function as photothermal agents. A preliminary measurement of the work density yielded 0.12 MJ/m3, but this value can probably be improved by better filling. Melting induced by light absorption in the wax interior provides advantages like a faster cycling time and lower energy consumption as compared to external heating by a laser or resistive heater.