随着新型储能技术、生物医学工程等前沿交叉领域的迅速发展，对微纳米尺
度下流体界面力学性质的表征与调控提出了新的需求。相较宏观流动，微纳尺度
下表面力效应凸显且涉及到多物理场耦合的问题，极大的增加了微纳尺度界面
力学性质研究的难度。另外，由于光学衍射极限的存在，传统的光学方法难以实
现对微纳尺度下界面流动及力学行为的表征。
因此，本文针对微纳尺度下流体界面力学性质的三个关键科学问题: 表征手
段、力学特性、调控机理开展了相关的工作。利用原子力显微镜在微纳尺度力学
测量及精确控制等优势，发展了导电型长针型悬臂探针技术对接触线动力学进
行研究，实现对接触线动力学与微观接触角动态行为的表征；结合胶体探针技术
对界面作用力进行表征。在此基础上，发现并阐明了电压调控下离子液体在金属
表面的接触角迟滞的转变；表征了离子液体限域环境下微纳尺度不同范围内的
界面力；实现了液-液相分离体系极低界面张力(10−4 N/m 量级) 的定量表征。本
文的主要研究内容及研究成果如下：

首先，针对离子液体微纳尺度润湿动力学的表征与调控问题，本文发展了导
电型长针式原子力显微镜技术，具备对流体界面精确操控和亚纳牛尺度力学表
征的双重优势；发现并阐明了离子液体在金属表面的接触角迟滞在电压调控下
的明显转变；通过分子动力学模拟展现了带电界面上由离子液体形成的类固层
结构和能量的演化。综合实验和模拟结果给出了一种不同于传统电润湿原理的，
通过电压调控离子液体界面层结构的排列和能量的势垒，从而引起流体界面接
触角迟滞转变的新机制。
其次，针对离子液体固-液界面多尺度力学表征的问题，本文采用胶体探针
结合原子力显微镜技术，实现了离子液体限域环境下微纳尺度不同范围内的界
面力学的表征；通过测量远距离流体黏滞阻力，定量表征了离子液体的黏度；测
量了离子液体双电层静电排斥力，展示了离子液体与传统稀电解质间的明显区
别；测量了近壁面间类固层的作用力，获得了类固层的结构与力学信息。

最后，针对极低界面张力的力学表征与生物相分离液滴力学性质的表征与
调控问题，本文通过长针式原子力显微镜技术对多肽相分离液滴及ATXN2 蛋白
相分离液滴的界面力学性质进行研究，实现了对极低界面张力（10−4 N/m 量级）
的定量表征，获得了生物相分离液滴的界面张力和黏度及其在盐浓度调控下的
改变，为后续研究生物相分离液滴的力学性质与生理功能间的联系提供基础。
以上工作发展的实验手段为研究微纳尺度流体界面力学行为提供了可行的
工具，为检验各类理论模型与数值模拟提供了可信数据，为探究界面上复杂现象
的物理本质提供参考。

With the rapid development of new energy storage technologies, biomedical engineering, and other cutting-edge interdisciplinary fields, there is a new need for the characterization and regulation of mechanical properties of micro- and nanoscale fluid interfaces. Compared with the macroscopic flow, the surface force effect at the micro and nanoscale is prominent and involves the coupling of multi-physical field, which
greatly increase the difficulty of the study of interfacial mechanical properties at the micro- and nanoscale. In addition, due to the existence of the optical diffraction limit, it is difficult to characterize the interfacial flow and mechanical behaviour at the microand nanoscale using traditional optical methods.

To address these challenges, we have conducted research on three key scientific problems: characterization methods, mechanical properties and regulatory mechanisms. Using the atomic force microscope, we have developed the conductive long needle cantilever probe technique to achieve the characterisation of the dynamic behaviour of contact
line dynamics with microscopic contact angles. Additionally, we have combined AFM with the colloidal probe technique to characterize interfacial forces. On this basis, we discover and elucidate the voltage-modulated transition of the contact angle hysteresis
of ionic liquids on metal surfaces, characterise the interfacial forces in different ranges of micro- and nanoscale in the ionic liquid confined environment, and achieve the quantitative characterisation of the very low interfacial tensions in the liquid-liquid phase-separation system (in the order of 10−4 N/m). The research focuses on the following three main areas.

Firstly, for characterizing and regulating the wetting dynamics of ionic liquid at the micro- and nanoscale, we develop a conductive long-needle AFM technique with the dual advantages of precise manipulation of fluid interfaces and sub-nano scale mechanical resolution. We discover and elucidate a significant shift of the contact angle hysteresis
of ionic liquids at metal surfaces under different voltages. We further demonstrate the structure and energy evolution of solid-like layers at electrified interfaces through molecular dynamics simulations. The combined experimental and simulation results demonstrate a new mechanism which is different from the traditional electrowetting. The arrangement of the interfacial layer structure of ionic liquids and the energy barriers are regulated by voltage, which causes a shift in the contact angle hysteresis at the fluid interface.

Secondly, to characterize the multi-scale mechanics of ionic liquid-solid interface, we adopt AFM technology with colloidal probe to achieve the interfacial mechanics of ionic liquids in different ranges of confined environment at the micro- and nanoscales. Through the measurement of long-distance hydordynamic force, we quantitatively measure the viscosity of ionic liquids. We further measure electrostatic repulsion force in
electrical double layer of the ionic liquids, which demonstrates a clear difference between ionic liquids and traditional dilute electrolytes. At last, we obtain the structure and mechanical information of the solid-like layer by measuring the structural forces near the metal surface.
Finally, to characterise and regulate the mechanical properties of biological phaseseparated droplets, we investigate the interfacial mechanical properties of peptide phaseseparated droplets and ATXN2 protein phase-separated droplets using long-needle AFM. We realise quantitative characterization of the very low interfacial tension (in order
of 10−4 N/m), and obtain the interfacial tension and viscosity of the phase-separated droplets as well as their changes under different salt concentrations. This lays the foundation of the subsequent research on the connection between the mechanical properties of the phase-separated droplets and their physiological functions.

The experimental tools developed in the above works provide feasible tools for studying the mechanical behaviour of fluid interfaces at the micro- and nanoscale. The above works provide reliable data for testing various theoretical models and numerical simulations, and provide references for investigating the physical nature of complex interfical phenomena.