Direct Laser Writing of Superhydrophobic PDMS Elastomers for Controllable Manipulation via Marangoni Effect

Abstract

Direct light‐to‐work conversion enables manipulating remote devices in a contactless, controllable, and continuous manner. Although some pioneering works have already proven the feasibility of controlling devices through light‐irradiation‐induced surface tension gradients, challenges remain, including the flexible integration of efficient photothermal materials, multifunctional structure design, and fluidic drag reduction. This paper reports a facile one‐step method for preparing light‐driven floating devices with functional surfaces for both light absorption and drag reduction. The direct laser writing technique is employed for both arbitrary patterning and surface modification. By integrating the functional layer at the desired position or by designing asymmetric structures, three typical light‐driven floating devices with fast linear or rotational motions are demonstrated. Furthermore, these devices can be driven by a variety of light sources including sunlight, a filament lamp, or laser beams. The approach provides a simple, green, and cost‐effective strategy for building functional floating devices and smart light‐driven actuators.

A Light‐Activated Polymer Composite Enables On‐Demand Photocontrolled Motion: Transportation at the Liquid/Air Interface

“…Soft materials have attracted more attention, given their potential in biomimetic motion, for developing novel mobile devices,f or example,t he rolling of wheels or helical ribbons and the imitation of aw ormlike crawl. [1] Apart from these mobile systems relying on solid bases,swimmers at liquid/air interfaces represent an advanced field in soft robots.B ioinspired by water striders,which can move quickly on the water surface by the Marangoni effect through secreting wax, [2] researchers have invented various devices based on the release of chemical additives,s uch as organic solvents [3] and surfactants, [4] to generate ad riving force through surface tension gradients.I nc onsideration of the controlled release and the exhaustion of these chemical additives,which serve as fuel, photothermal effect based devices have been fabricated [5] by utilizing the temperature response of surface tension. However,t he complexity of the field of surface tension restricts precise regulation of the motion and always requires elaborate design of the shape of the devices.…”

A Light‐Activated Polymer Composite Enables On‐Demand Photocontrolled Motion: Transportation at the Liquid/Air Interface

“…This facile on-off control is superior to most chemical Marangoni-effectbased motors. [5] Figure 2c also demonstrates the steady speeds increased from 0.4 cm s À1 to 1.0 cm s À1 ,without asignificant difference in the acceleration time,when the light power was increased from 50 mW cm À2 to 150 mW cm À2 ,r espectively.T his facile velocity control through remote regulation of light intensity could be attributed to the facts that both the photomechanical deformation Ap ossible motion mechanism of the bilayer structured swimmer is proposed and is analogous to the "dolphin kick", which is also referred to in other stimuli-responsive artificial swimmers. According to the fitted curves of the displacement-time relationship,t he velocity-time curves were deduced, as given in Figure 2c.I ti sw orth emphasizing that the motion started immediately upon exposure to UV light and reached as table velocity within only 1.5 seconds.…”

“…It is expected that the temperature change on the liquid surface is even smaller because of the larger thermal capacity of the liquid and the dynamically continuous motion of the swimmer. [5] To further exclude the thermal effect of direct illumination on the liquid, an effect which might cause thermal convection and evaporation, we observed the performance of aK apton film (8.0 mm 8.0 mm) without the LCN layer under the same conditions. Besides,t he bilayer swimmer still functioned after dissolving surfactant (sodium dodecyl sulfate), which can quench the motion in photothermal systems, in the ethanol/water mixture.…”

“…[1] Apart from these mobile systems relying on solid bases,swimmers at liquid/air interfaces represent an advanced field in soft robots.B ioinspired by water striders,which can move quickly on the water surface by the Marangoni effect through secreting wax, [2] researchers have invented various devices based on the release of chemical additives,s uch as organic solvents [3] and surfactants, [4] to generate ad riving force through surface tension gradients.I nc onsideration of the controlled release and the exhaustion of these chemical additives,which serve as fuel, photothermal effect based devices have been fabricated [5] by utilizing the temperature response of surface tension. [1] Apart from these mobile systems relying on solid bases,swimmers at liquid/air interfaces represent an advanced field in soft robots.B ioinspired by water striders,which can move quickly on the water surface by the Marangoni effect through secreting wax, [2] researchers have invented various devices based on the release of chemical additives,s uch as organic solvents [3] and surfactants, [4] to generate ad riving force through surface tension gradients.I nc onsideration of the controlled release and the exhaustion of these chemical additives,which serve as fuel, photothermal effect based devices have been fabricated [5] by utilizing the temperature response of surface tension.…”

“…[5] Thes trip length was fixed at 2.0 cm, double the diameter of the light spot so that the illumination could be focused on aquarter of the strip.A ss hown in Figure 3d,u nilateral photoirradiation provides atorque instead of thrust, leading to the rotation of the strips like ad olphin beating its pectoral fin, while changing the irradiation site to the other side of strip can reverse the rotation direction. Figures 3a-c and Movie S5 show the light-powered clockwise rotation of one strip (2.0 cm 4.0 mm) under UV irradiation (150 mW cm À2 ), and it was conveniently obtained without the additionally complicated structure design of other systems.…”