Green Sorbitol-Based Deep Eutectic Solvents Enabling Near Zero-Wear of Steel–Steel Tribopairs

Abstract

Deep eutectic solvents have emerged as promising alternatives to traditional lubricants due to their ease of preparation, low cost, low/no pollution, reproducibility, and unique antifriction and antiwear performance. Herein, green sorbitol-based deep eutectic solvents are successfully synthesized using d-sorbitol and quaternary ammonium salts as hydrogen bond donors and acceptors, respectively, through a simple heating and stirring method. The synthesized sorbitol-based deep eutectic solvents exhibit good thermostability, high viscosity, and favorable wettability on the steel surface. Notably, tribological tests demonstrated that the sorbitol-based deep eutectic solvents displayed outstanding antiwear and friction-reducing properties and were observed to achieve nearly wearless behavior on the steel surface under high contact pressure (2.16 GPa). X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy revealed that complex tribofilms were formed because of the tribochemical reactions and physical adsorption of deep eutectic solvents on steel substrates, resulting in outstanding tribological properties. These results demonstrate that the as-synthesized sorbitol-based deep eutectic solvents are promising candidates for green and sustainable lubricating materials with eminent tribological properties. Furthermore, the present work may provide guidance and reference for the development of green and high-performance deep eutectic solvent-based lubricating materials.

Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman

“…With the increase of TEOA content, the ratio of strong H-bonds to total H-bonds ( A s / A t ) in ILAs decreases from 0.68 to 0.42, and the FTIR spectra of the ILAs also show the existence of H-bond peaks at 3100–3600 cm –1 in the ILAs (Figure S1). These results indicate that the H-bonding interactions between Cl – and TEOA are strong H-bonding interactions. , The chemical shift at 4.36 ppm is considered to be the H response signal in its –OH based on the 1 H NMR data of TEOA (Figure d); however, as the proportion of TEOA in ILAs increases (i.e., from ILA 1:2 to ILA 1:20 ), the chemical shift shifts from 4.47 to 4.39 ppm (i.e., Δ δ = 0.081, Figure e), gradually approaching that of TEOA, and the viscosity decreases from 0.41 to 0.34 Pa·s (Figure S2). This suggests that the weak interactions between components in ILAs, especially H-bonding interactions, are directly related to the content of TEOA, and they may affect the viscosity of the involved ILAs.…”

Intrinsically Self-Driven Humidity Actuators Based on Silk Nanofibers Exfoliated Using a Deep Eutectic Solvent

“…16 Deep eutectic solvents (DESs) are eutectic mixtures of two or more components combined by hydrogen bonding interactions with a melting point lower than the eutectic point of each individual component. 21 DESs have the advantages of low toxicity and volatility, high biocompatibility and degradability, and a green economy. By appropriately combining different quaternary ammonium salts (e.g., ChCl) with different hydrogen bond donors, DES with different physicochemical properties (e.g., freezing point, viscosity, conductivity, etc.)…”

“…Deep eutectic solvents (DESs) are eutectic mixtures of two or more components combined by hydrogen bonding interactions with a melting point lower than the eutectic point of each individual component . DESs have the advantages of low toxicity and volatility, high biocompatibility and degradability, and a green economy.…”