Structural Color Surface on Transparent PDMS Fabricated by Carbon-Assisted Laser Interference Lithography for Real-Time Quantification of Soft Actuators Motion

Abstract

Dynamic and real-time monitoring of the motion state of soft actuators is of great significance for optimizing their performance. However, present noncontact measurement approaches based on diffractive groove arrays fabricated by imprinting have some limitation, e.g., the grooves should be processed before the solidification of soft materials or the depth and period of grooves cannot be flexibly adjusted. Here, a flexible and highefficiency fabrication approach carbon-assisted laser interference lithography (CLIL) for periodical groove structures with structural color is proposed. This technique is to irradiate the interference laser on the PDMS surface coated by a carbon layer, which is used for enhanced laser absorption. The processing parameters are systematically studied and optimized to achieve a bright structural color. Benefiting from the advantages of CLIL, the structural color can be processed on a solidified transparent surface with controllable characteristics such as groove period and depth. Lastly, the motion of an electric-driven actuator can be real-time quantified by calibrating the relationship between the observation angle and the observed structural color.

Recent advances in colour-tunable soft actuators

“…[56][57][58][59] When soft actuators deform into different geometries, the diffraction light of the PCs can be remarkably changed. 33,60 (2) Tuning the lattice distance. The PBG of the PCs can be precisely modulated via the distances between lattice points.…”

“…The PBG of the PCs can be precisely modulated via the distances between lattice points. 33,36,61,62 Hence, the structural colour can directly respond to the deformation of actuators under external stimuli (Fig. 1B) such as light, 63 vapour, 64 heating, 65 force, [66][67][68] magnetism, 69 etc.…”

“…Owing to the excellent stability, high lustre and adjustability of structural colour, structural colour-tunable soft actuators have provided wide application prospects, especially in the fields of soft robotics, wearable electronic devices for visible environmental detection and health monitoring. 33,34,60,64,65,69,[84][85][86][87][88][89] Notably, structural colour-tunable soft actuators can realize reversible and irreversible colour changes via employing different polymer matrices. For example, introducing reversible (liquid crystal elastomers, 34,63,86 hydrogels 65,69 ) or irreversible (shape memory polymers 90,91 ) stimuli-responsive polymers into the periodic micro/nano structures of the structural colour-tunable soft actuators can simultaneously tune the lattice parameters during the reversible or irreversible deformation processes.…”

“…60 Additionally, flexible and high-efficiency fabrication approaches using carbon-assisted laser interference lithography (CLIL) for periodic microgroove structures could also yield iridescent structural colours via optical grating diffraction. 33 Due to the one-dimensional long-rangeordered structure, the laser-irradiated surface of the PDMS shows brilliant and tunable structural colours sensitive to viewing angles. In addition, the structural colour can be generated on the surface of an electric-driven actuator and quantified in real-time by calibrating the relationship between the viewing angle and the spectrum of structural colours.…”

“…For example, soft actuators with static periodic structures can change their structural colours via tuning different viewing angles, while they show limited controllability in colour change due to their fixed lattice distance. 33 Soft actuators with dynamic periodic structures which have a stimuli-responsive matrix are commonly used to realize structural colour changes as their periodic spacings can be changed by macroscopic deformations of the matrix in response to specific stimuli. 34 The sensitivity and contrast of the structural colour-tunable soft actuators can be further improved using some specifically designed structures.…”