Deep-eutectic solvents enable tunable control of the micro-mechanical response through electrical actuation

Abstract

Active interactions at liquid-to-solid interfaces can significantly impact the mechanical response of solid substrates. Traditionally, these have been regulated through surface-active media, such as ionic liquids, used in a static (time-invariant) manner that relies on chemical tuning to induce specific mechanochemical responses. This study introduces a novel and sustainable class of Deep Eutectic Solvents (DESs) to demonstrate a dynamic (time-variant) mechanochemical effect, achieved through molecular electro-actuation at the fluid-to-solid interface. The dynamic micro-mechanochemical effect was demonstrated using a DES mixture consisting of citric acid and choline chloride in a 1:1 M ratio, applied to a nickel single-crystal micro-cantilever substrate. The findings show how the DES coating alone induced compressive surface stress, resulting in a 34 % increase in principal stress. More notably, when the substrate surface was polarized with a ±5 V potential, electro-actuation amplified this mechanochemical effect by up to 51 %, confirming a clear dynamic response. Further validation was presented at the macroscale in a polycrystalline material setting, where a similar response was observed. These findings give insight into the possible development of smart surfaces coated with DESs, where a single chemical system can dynamically alter materials’ mechanical response through simple electro-actuation, offering versatile applications across micro and macro scales.