Bioinspired near-infrared light-induced ultrafast soft actuators with tunable deformation and motion based on conjugated polymers/liquid crystal elastomers

Abstract

Light-responsive liquid crystal elastomers (LCEs) are one kind of attractive and fascinating materials in developing untethered and dexterous bioinspired robotic systems. Unlike widely explored azobenzene-containing LCE actuators utilizing photoisomerization, near-infrared (NIR) light-actuators based on photothermal effects from inorganic nanoparticles offer many benefits in terms of the response time, magnitude of actuation, and manipulation flexibility. However, unwanted aggregation of these nanoparticles in the LCE network tends to bring about uneven local heating, which is undesirable for repeated controllable shape morphing and motions. In this study, we synthesized a novel organic photothermal dopant, conjugated polymers (CPs), via palladium-catalyzed Stille cross-coupling polymerization by using donor monomer diketopyrrolopyrrole (DPP58) and acceptor monomer (TBZ12), and introduced them in the LCE for forming soft CPs/LCE actuators. These CPs with planar molecular structures exhibited good dispersion in the LCE mixture. A low content (0.3 wt%) of the conjugated polymers in the LCE matrix could result in an ultrafast increase in local temperature under 808 nm NIR irradiation. Using a surface-patterned glass substrate, a single film with splay alignments was allowed to be fabricated via UV photopolymerization. The 60 μm-thick CPs/LCE film actuators exhibited a superior photothermal effect, repeatable shape change, and ultrafast response time with actuation within 1 s upon 808 nm laser irradiation. Tunable shape deformation, including bending, “Swiss” rolling and helical twisting, was realized by choosing a cutting strategy at angles oblique to the alignment direction and unsymmetric NIR light illumination. The film could bend up to 180° within 3 s and recover its initial shape within 4 s. Photomotility of the millimeter-scale CPs/LCE actuator was also demonstrated through successive left-hand helical twisting at an average motion speed of 0.47 mm s⁻¹. The development of soft, NIR light-driven CP-doped LCE actuators would offer a promising path toward micromachines and untethered soft robotics.