二维材料黏附接触中的熵效应

Two-dimensional (2D) materials, which have been the a new star in material science in the last decade, are crystalline materials consisting of a single layer of atoms. Due to their unusual performance, 2D materials have been seen as building blocks in high-tech areas including electronics, biological sensor, nanodevices integration, etc. However, as materials consist of only surface atoms, adhesion has been a major mechanical issue in 2D material’s experimental studies and device applications. Recent research, including our works, reveals that the adhesion of 2D materials to other surfaces is significantly influenced by thermal fluctuations. There in fact exists heat release/absorption in the attachment/detachment of a 2D material onto/from a substrate, indicating that the adhesion of 2D materials is like gas adsorption rather than solid adhesion. Understanding the underlying mechanism and how adhesion entropy relays on real factors during adhesion is the key to develop adhesion theory and intrigue real applications of 2D materials. In this project, we intend to answer these questions by systematically studying the adhesion process of 2D materials onto solid surface via MD simulations and theoretical modeling based on lattice dynamics. In addition, we aims using large scale MD simulations to investigate the role of adhesion entropy in several temperature-dependent phenomena that found in recent experimental researches. The expected results of this project will promote the stage of nanoscale adhesion theory, and benefit the applications of nanoscale devices.

二维材料是一类新兴的纳米材料，在量子计算、纳米机电系统、生物传感等高新技术领域，有广泛的应用前景。而二维材料与其衬底表面之间的黏附问题是目前二维材料研究中重点关注的力学问题之一。最近的研究揭示（包括申请人的工作），二维材料的黏附中存在显著的熵效应，导致其黏附行为呈现出气体吸附中的吸热和放热特征。深入理解熵效应的物理机制、发展准确描述熵效应的解析模型，是深入理解二维材料黏附的关键。本项目拟采取分子动力学结合基于晶格动力学的解析模型，对黏附过程中熵效应的物理机理，熵效应对尺寸等因素的依赖，以及熵力的微观起源等问题开展更深入系统的研究。在此基础上，针对实验研究中报道的一些温度依赖的黏附现象，我们将结合分子动力学和解析数值方法系统探讨熵效应在这些现象中起的作用。项目预期成果对深入认识纳尺度黏附行为，发展纳尺度黏附理论，以及推动纳尺度器件应用有积极的科学意义。

二维材料是一类由单层原子构成的纳米材料，其结构决定二维材料有优异的电学、热学、力学性能，使得二维材料被认为是构筑微纳米电子机械系统的基础材料。二维材料中所有原子都是表面原子，而黏附现象是一种表面现象，这决定了黏附在二维材料的制备合成、功能器件化等方面有着至关重要的影响。二维材料是一种固体材料，研究其黏附也一般在固体表面黏附的框架中进行。本课题研究揭示，二维材料的黏附类似于气态黏附，在其黏附和脱附过程中存在着显著的放热和吸热现象。. 二维材料的气态黏附特征的物理机理是黏附过程中结构熵的变化。二维材料黏附于基底时，原子受到更多的约束，导致其结构熵减小，系统释放热量。通过对多壁碳纳米管层间运动的研究，揭示碳纳米管中同样存在这一过程。黏附熵也可以用来解释碳纳米管中一系列跟温度有关的现象，如碳管的热泳、碳管的可逆塌缩等。这些和温度有关的现象说明，结构熵可以在微纳米尺度提供一种新的驱动方式。. 通过研究二维材料和黏附有关现象，如摩擦、弹性热效应等，本课题进一步揭示黏附熵的普遍存在以及黏附熵对这些现象的影响。. 通过分析黏附过程的晶格振动，我们建立了黏附熵的解析模型，进一步分析了影响黏附熵的因素。这为将来理解和进一步应用黏附熵提供了理论指导。