Electrically Tunable Friction: From Sticky to Slippery with Ionic Hydrogels

Abstract

Abstract Real‐time regulation of friction from conventional dry states to ultra‐low levels represents a critical strategy for improving energy efficiency and enabling the intelligent design of adaptive systems. Yet, current friction‐control methods typically achieve only modest modulation and often rely on liquid lubricants at macroscopic scales, which impose stringent sealing requirements and limit practical applications. Here, an electric‐field strategy is reported for friction modulation using a polyvinyl alcohol‐based ionic hydrogel as an electroresponsive frictional material. During sliding against a metal ball, the friction coefficient (COF) can be reversibly modulated by more than fifty‐fold under low voltage control (−30 V to +30 V), without the need for external lubricants. Remarkably, the COF decreases to 0.03 at −30 V (with the metal ball connected to the negative pole), while at 0 V or +30 V it increases to 1–2. Mechanistic analyses reveal that positive charging of the ionic hydrogel triggers electroosmotic extraction of a salt‐rich interfacial layer, driving the dramatic reduction in friction. It further demonstrates the first crawling robot and precision robotic arm manipulation powered by electrotunable friction, establishing a new paradigm for adaptive and energy‐efficient robotic and mechanical systems.