A plant tendril mimic soft actuator with phototunable bending and chiral twisting motion modes

Abstract

In nature, plant tendrils can produce two fundamental motion modes, bending and chiral twisting (helical curling) distortions, under the stimuli of sunlight, humidity, wetting or other atmospheric conditions. To date, many artificial plant-like mechanical machines have been developed. Although some previously reported materials could realize bending or chiral twisting through tailoring the samples into various ribbons along different orientations, each single ribbon could execute only one deformation mode. The challenging task is how to endow one individual plant tendril mimic material with two different, fully tunable and reversible motion modes (bending and chiral twisting). Here we show a dual-layer, dual-composition polysiloxane-based liquid crystal soft actuator strategy to synthesize a plant tendril mimic material capable of performing two different three-dimensional reversible transformations (bending versus chiral twisting) through modulation of the wavelength band of light stimuli (ultraviolet versus near-infrared). This material has broad application prospects in biomimetic control devices.

Figure 1. Design and synthesis of dual-layer polysiloxane-based liquid crystal soft actuators.

(a) The photo image of a cucumber plant tendril with bending and chiral twisting distortions. (b) The chemical compositions of PMHS-AZO46-MBB/YHD796 composite (Formula 1) and PMHS-MBB/YHD796 composite (Formula 2). (c) Schematic illustration of the preparation protocol of the dual-layer LCE ribbon material.

Figure 2. Thermal and optical absorption properties of the dual-layer LCE film.

(a) Differential scanning calorimetry curves of the LCE sample containing not only PMHS-AZO46-MBB/YHD796 composite but also PMHS-MBB/YHD796 composite. (b) Ultraviolet–vis spectra of YHD796, AZO46, PMHS-MBB/YHD796 and PMHS-AZO46-MBB/YHD796 composite films dispersed in CH₂Cl₂ with a concentration of ca. 1.4 × 10⁻³ mol l⁻¹.

Figure 3. Ultraviolet-induced bending behaviour of two bilayer LCE ribbons.

The bilayer LCE ribbon with a (a) 45° or (b) −45° angle between the top and bottom layer was irradiated under 365 nm ultraviolet light. (c) The bilayer ribbon (θ=45°) was turned upside down and irradiated under 365 nm ultraviolet light. Supplementary Movies 1–3 show these scenarios in motion. (d) The included angle α vs ultraviolet illumination time diagram of the bilayer LCE ribbons. The error bars indicate the standard deviation of the measured angles. (e) Curvature (1/r) of the bilayer LCE ribbons as a function of ultraviolet illumination time. The error bars indicate the standard deviation of the bending curvature calculated from the included angle data.

Figure 4. Near-infrared-induced chiral twisting behaviour of two bilayer LCE ribbions.

The bilayer LCE ribbon with a (a) 45° or (b)−45° angle between the top and bottom layer was irradiated under an 808 nm near-infrared light for 8 s. Supplementary Movies 4 and 5 show these scenarios in motion. (c,d) Temperature versus near-infrared illumination time diagrams of the two bilayer LCE ribbons. The error bars shown in (c) and (d) represent the standard deviation of the measured surface temperature data of two bilayer LCE samples.

Figure 5. ultraviolet and near-infrared photoresponsive behaviours of a same-sized-bilayer LCE ribbion.

(a) Schematic illustration of the preparation protocol of a same-sized-bilayer LCE ribbon material whose top layer was of the same size as the bottom layer. The bilayer LCE ribbon with a −45° angle between the top and bottom layer was irradiated under (b) 365 nm ultraviolet light and (c) an 808 nm near-infrared light, respectively. Supplementary Movies 6 and 7 show these scenarios in motion.