中国科学院力学研究所机构知识库

      移动接触线是指两种互不相溶的流体在固体表面形成的移动三相接触区域，其内部三相物质之间的相互作用影响着整个流场的动力学特性。由于在绿色能源、柔性电子、生命健康和微纳化工等国家重大领域的重要应用和迅速发展，移动接触线在新的应用背景下发展了新的难题—力电耦合下多相流体、纳微颗粒等在微型装置、岩层和生物体等受限空间中的流动与输运特性成为限制这些重要领域发展的瓶颈难题。因此，亟需发展新方法和理论以探究力电耦合、流固耦合等多效应作用下的液-液界面动力学、固-液界面动力学及固-固界面动力学，以揭示力电耦合下移动接触线的动力学特性，为多物理场中“Huh-Scriven佯谬”探索解答，从而有效的控制移动接触线，以期对实际应用提供指导和预测。

      本文针对多相液体体系中移动接触线的力电耦合效应及电毛细剥离中移动接触线的动力学机理两个关键科学问题，采用物理力学方法，通过跨尺度实验研究与表界面物理力学理论分析相结合的方法开展研究，主要分为力电场下液-液界面的黏性失稳行为研究、固-固界面的毛细剥离动力学研究及电解效应下毛细剥离动力学研究三个部分。

       首先，针对移动接触线的跨尺度特征，本文在课题组跨尺度物理力学研究平台的基础上建立了力电场下移动接触线的跨尺度研究平台，具备跨尺度制备、表征和分析的功能。利用力电场下移动接触线的跨尺度研究平台，开展了力电耦合作用下移动接触线的稳定性及剥离行为研究。

       其次，针对液-液界面黏性失稳的有效控制这一难题，本文开展了力电耦合下黏性指进行为的主动调控研究，实现了电场下Maxwell应力对黏性指进行为的促进与抑制，建立了力电耦合下纳微流动中黏性指进行为的控制方程，揭示了电场下Maxwell应力与静水压强之间的竞争关系，为受限液体流动中液-液界面不稳定性的应用与调控开辟了新的途径。

      第三，针对力电场下液-固界面稳定性及毛细剥离动力学特性，本文通过对力电场下受限液体的毛细剥离动力学研究，提出了“电毛细剥离”的全新模式。该方法通过施加电场诱导液膜润湿界面结合层来实现薄膜的剥离，具有主动调控、无损、易实现及几乎适用所有类型薄膜的优点。电毛细剥离动力学研究为固-固界面的分离提供了新思路，为柔性材料的分离、转印及重复利用提供了新的途径。

      最后，为了厘清力电耦合多效应对电毛细剥离行为的影响，本文通过对电解效应下电毛细剥离动力学研究，厘清了电解效应下界面特性、润湿行为及剥离规律。在实验基础上，我们建立了电毛细剥离过程液滴铺展行为的润湿模型，揭示了电解效应对电解质液滴铺展过程钉扎力及铺展电压的影响关系，为实现快速、稳定的电毛细剥离提供理论支撑。

      综上所述，本文系统地研究了力电耦合场作用下移动接触线的稳定性及毛细剥离动力学行为，提出了纳微流动中黏性指进的主动调控方法、电毛细剥离的新概念，揭示了力电耦合多效应对电毛细剥离行为的影响，对深入理解多场耦合作用下移动接触线的动力学机理与现象规律具有重要意义，为受限液体流动与输运的主动调控提供了新的途径。

      Moving contact line (MCL) is the three-phase region formed by two impermeable fluids moving on a solid surface, where the interaction among phases influences the dynamic behavior of the entire fluid field. Owing to its significant applications and rapid development in the fields of green energy, flexible electronics, life and health, micro/nano chemical engineering, etc., new challenges emerge in MCL problems. The flow and transport characteristics of multiphase fluids and nanoparticles at confined spaces such as microdevices, rock layers, and organisms under the electro-mechanical coupling have become bottleneck problems that limit the development of these important fields. Therefore, it is urgent to develop new methods and theories to explore the dynamic of liquid-liquid interface, solid-liquid interface, and solid-solid interface under multiple effects of electro-mechanical coupling and fluid-structure interaction. This is for revealing the dynamic characteristics of MCL under electro-mechanical coupling, exploring the answer to the “Huh-Scriven paradox” in multi-fields, which provides guidance and prediction to control the moving contact line in practical applications.

      This dissertation focuses on two key scientific issues: the dynamic characteristics of contact line in confined liquid under electro-mechanical coupling and the dynamic mechanism of capillary peeling of confined liquid under electro-mechanical coupling. Physical mechanics methods are used to conduct research through a combination of cross-scale experiments and physical mechanics theory analysis. The dissertation is divided into three parts: the viscous instability of the liquid-liquid interface, the electro-capillary peeling of the solid-solid interface, and the electrolysis effects on the electro-capillary peeling under the electro-mechanical coupling.

      Firstly, regarding the cross-scale characteristics of MCL, this dissertation independently established the liquid-liquid and the solid-solid experimental modules under an electro-mechanical field, which has the functions of cross-scale preparation, characterization, and analysis. In the experiment, we used this experimental platform to investigate the electro-mechanical effect of liquid-liquid interface instability and solid-solid interface capillary peeling of MCL.

      Secondly, in response to the challenge of effectively controlling the viscous fingering at the liquid-liquid interface, this dissertation performed the viscous fingering study under an electro-mechanical field and demonstrates firstly the promotion and suppression of viscous instability by Maxwell stress under an electric field. The working mechanism of viscous instability under electro-mechanical coupling is established, which reveals that the active control of viscous instability is achieved by the competition between Maxwell stress and hydrostatic pressure. This work opens up new avenues for the application and regulation of liquid-liquid interfacial instability in the confined liquid.

      Thirdly, regarding the stability of the liquid-solid interface and dynamic characteristics of capillary peeling under electro-mechanical coupling, we propose an “electro-capillary peeling” strategy by studying the capillary peeling under an electro-mechanical field. This strategy achieves thin film detachment by driving liquid to percolate and spread into the bonding layer under electric fields. The electro-capillary peeling method has the advantages of active regulation, non-destructive, and easy operation, and is almost applicable to all types of thin films. The study of electro-capillary peeling provides a new way for the detachment of thin films and facilitates valid avenues for reusing soft materials.

      Finally, to clarify the multi-effect under an electro-mechanical field on electro-capillary peeling, this dissertation conducted a study to investigate the electrolysis effect on electro-capillary peeling behavior, including interface characteristics, wetting behavior, and peeling law. Based on the experiment, a wetting model is established to reveal the electrolysis effect on the spreading behavior of liquid droplets during the electro-capillary peeling, which provides the guidelines for achieving rapid and stable electro-capillary peeling.

      In summary, this dissertation systematically studied the stability and capillary peeling of contact line in confined liquid under electro-mechanical coupling, proposed an active control method for viscous fingering, an electro-capillary peeling strategy, and clarified the electrolysis effect on electro-capillary peeling. This dissertation is of great significance for an in-depth understanding of the dynamic mechanism and phenomenon rules of MCL under multi-field coupling and provides a new way for active control of confined liquid flow and transport.