Electrothermal and humidity-responsive flexible actuator with asymmetric eutectic gallium-indium/cellulose nanofiber composite film printed by electrohydrodynamics

Abstract

High-performance dual-responsive flexible actuators are crucial for soft robots, artificial muscles, and wearable devices. However, a simple and fast preparation of dual-responsive flexible actuators with excellent actuation performance remains a challenge. Herein, an electrohydrodynamic (EHD) printing method is proposed to prepare eutectic gallium-indium/cellulose nanofiber (EGaIn/CNF) film with asymmetric structure. EGaIn/CNF film is assembled with polyethylene (PE) with high anisotropic thermal expansion coefficient to fabricate an EGaIn/CNF-PE bilayer flexible actuator with gradient structure. Through the collaborative design of materials and structures, combined with the high conductivity of gradient-distributed EGaIn, excellent hygrosensitivity of gradient-distributed CNF, and high thermal expansion coefficient of PE, the EGaIn/CNF-PE flexible actuator exhibits excellent actuation performance under electrothermal and humidity response. The flexible actuator achieves a bending curvature of 3.3 cm⁻¹ within 12 s under a low voltage of 4 V, and bending curvature of 3.06 cm⁻¹ under a 30 % change in environmental humidity. Moreover, the fabricated flexible actuator is applied in the fields of flexible gripper, smart flexible switch, and biomimetic flower, which shows its commendable practical application potential.