Opto-thermoplasmonic pneumatic pistons actuator

Abstract

Optical manipulation of liquids has extensive applications, ranging from biological research to information technology. However, existing technologies struggle with a fundamental limitation, as the pinning force of the contact line significantly resists liquid motion. In this study, a novel strategy is introduced to govern fluid motion and overcome this barrier. Our approach involves positioning a nanofluid slug within a sealed capillary tube and directing irradiation to one side of the slug. Intensive local vaporization of nanofluid is generated due to the thermo-plasmonic effect of nanoparticles, leading to a considerable driving force and rapid motion of the slug. Based on this principle, the opto-thermoplasmonic pneumatic piston was proposed. The direction of motion is controlled by modulating the laser irradiation direction. Furthermore, the laser beam parameters enable adjustable piston oscillation frequency and speed. To better understand the characteristics of the opto-thermoplasmonic pneumatic piston, theoretical studies were conducted to analyze the kinetic characteristics of the piston, revealing an expression consistent with the Kelvin-Voigt model. Various factors affecting the performance of the pneumatic pistons were also studied. Based on the experimental results and motion model, we found and explained that the oscillation amplitude presents an exponential relationship with the working frequency $l_a=a(1-e^{-f_a^{-1}/b})$, where the coefficient a is related to the laser power, slug length, and nanofluid concentration, while the coefficient b is solely dependent on the nanofluid concentration. These opto-thermoplasmonic pneumatic pistons epitomize a new paradigm for manipulating aqueous mesoscopic systems, thus forging new paths for light-propelled soft motors with precise motion control.