Asymmetric Contact Synergy of Unequal-Sized Soft and Hard Clusters in Highly Concentrated ZnCl2 for Heterogeneous Superlubricants

IF 2.9 3区 工程技术 Q2 ENGINEERING, CHEMICAL
Manqiang Liu, Hongyu Liang, Xinjie Chen, Tianqiang Yin, Yongfeng Bu
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Abstract

Low ionic concentrations and the chemical stability of the ions involved to water are considered necessary for hydrated ionic solution lubricants. Herein, an ultra-high concentration of chemically active ZnCl2 aqueous solution (up to 20 mol L− 1) is first reported to be used as a liquid superlubricant, with trace amounts of Zn2+ hydrolyzed to generate Zn(OH)2 (i.e., hard clusters) in addition to Zn2+ hydrated with water (i.e., soft clusters), resulting in the formation of heterogeneous phases with a mixture of soft and hard clusters. The coefficient of friction (COF) inversely correlates with the molar concentration of ZnCl2, where the COF of the optimized samples can be as low as 0.006 with a stable macroscopic superlubricated state; the particle size distribution of clusters and their corresponding Spans, however, are positively correlated with the molar concentration, suggesting that asymmetric contact between these unequal-sized soft and hard clusters contributes greatly to the reduction of interfacial shear resistances. This ultra-high-concentration aqueous solution superlubricant not only breaks the convention but also deepens the mechanism of liquid superlubricity from the perspectives of cluster size distribution and interactions between clusters, providing a new insight into the design of advanced water-based ionic solution superlubricants.

Graphical Abstract

Abstract Image

高浓度 ZnCl2 中大小不等的软硬团簇的非对称接触协同作用,用于制造异质超级润滑剂
低离子浓度和离子对水的化学稳定性被认为是水合离子溶液润滑剂的必要条件。本文首次报道了一种超高浓度的化学活性 ZnCl2 水溶液(高达 20 mol L-1)可用作液体超级润滑剂,其中除了与水水合的 Zn2+(即软簇)外,还有微量的 Zn2+水解生成 Zn(OH)2(即硬簇),从而形成软簇和硬簇混合的异质相。摩擦系数(COF)与 ZnCl2 的摩尔浓度成反比,优化样品的 COF 低至 0.006,具有稳定的宏观超润滑状态;然而,团簇的粒度分布及其相应的 Spans 与摩尔浓度成正比,表明这些大小不等的软硬团簇之间的非对称接触在很大程度上有助于降低界面剪切阻力。这种超高浓度水溶液超级润滑剂不仅打破了常规,而且从团簇粒度分布和团簇之间相互作用的角度深化了液体超级润滑的机理,为设计先进的水基离子溶液超级润滑剂提供了新的见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Tribology Letters
Tribology Letters 工程技术-工程:化工
CiteScore
5.30
自引率
9.40%
发文量
116
审稿时长
2.5 months
期刊介绍: Tribology Letters is devoted to the development of the science of tribology and its applications, particularly focusing on publishing high-quality papers at the forefront of tribological science and that address the fundamentals of friction, lubrication, wear, or adhesion. The journal facilitates communication and exchange of seminal ideas among thousands of practitioners who are engaged worldwide in the pursuit of tribology-based science and technology.
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