A theoretical analysis of the surface dependent binding, peeling and folding of graphene on single crystal copper

The binding, peeling and folding behavior of graphene on different surfaces of single crystal copper were examined theoretically. We show that the binding energy is the highest on the Cu(111), and follows the order of Cu(111) > (100) > (110) > (112). Conventional theory is capable of capturing the dynamic process of graphene peeling seen from molecular dynamics simulations. We show that the number of graphene layers on Cu surfaces could be distinguished by performing simple peeling tests. Further investigation of the folding/unfolding of graphene on Cu surfaces shows that Cu(111) favors the growth of monolayer graphene. These observations on the interaction between graphene with single crystal Cu surfaces might provide guidelines for improving graphene fabrication

Tunable Mechanical Behavior of Carbon Nanoscroll Crystals Under Uniaxial Lateral Compression

A theoretical model is developed to investigate the mechanical behavior of closely packed carbon nanoscrolls (CNSs), the so-called CNS crystals, subjected to uniaxial lateral compression/ decompression. Molecular dynamics simulations are performed to verify the model predictions. It is shown that the compression behavior of a CNS crystal can exhibit strong hysteresis that may be tuned by an applied electric field. The present study demonstrates the potential of CNSs for applications in energy-absorbing materials as well as nanodevices, such as artificial muscles, where reversible and controllable volumetric deformations are desired

Study on the Mechanical Behaviors of Graphene and Its Nano-structure

石墨烯是新近发现的二维材料，由于有着优异的物理性质和广泛的应用前景而受到了大量的关注和研究。本文主要基于石墨烯及其各种衍生物的弯曲弹性能和相互作用能的耦合，运用理论建模和分子动力学模拟的方法，研究石墨烯及其纳米结构在与自身或其他物体相互作用时的力学行为。 石墨烯条带与碳纳米管相互作用时，由于范德华力的影响，石墨烯条带会自发地缠绕在碳纳米管上，并形成两种可能的基本缠绕方式：helix型缠绕和scroll型缠绕。而条带最终选取的缠绕方式与条带的弯曲弹性能，碳纳米管-条带之间的相互作用能，条带-条带之间的相互作用能三者相关联。本文用解析的方法建立了条带缠绕方式与上述三种能量参数之间关系的理论模型，并且绘出根据物理、几何参数预测缠绕方式的相图，并且通过分子动力学模拟的方法验证了该模型的准确性。 石墨烯制成的碳纳米卷可规则密排从而形成碳纳米卷晶体。这种晶体在受到外界的侧向压缩载荷时，其力学性能的本质是碳纳米卷与自身或邻近碳纳米卷之间的相互作用。本文建立了这种相互作用的理论模型，并通过分子动力学模拟的方法验证。结果发现这种晶体在受到侧向压缩载荷时会产生迟滞效应进而产生能量耗散。耗散的大小可以通过调节相互作用能大小的方式调节。这个发现说明碳纳米卷晶体可用于制备成能量吸收材料。 石墨烯片与单晶铜之间相互作用时，单晶铜的各个晶面与石墨烯结合强度由强到弱分别为（111）>（100）>（110）>（112），同时折叠的石墨烯在铜（111）面上不能保持折叠的形式，而是会自发地展开，说明铜（111）面是最适用于利用化学气相沉积法制备石墨烯的晶面。石墨烯片从单晶铜上剥离的研究结果表明，传统的剥离模型可以用于描述石墨烯的剥离过程，被剥离石墨烯的层数也可以通过剥离试验来确定

Mechanics of rolling of nanoribbon on tube and sphere

The configuration of graphene nano-ribbon (GNR) assembly on carbon nanotube (CNT) and sphere is studied through theoretical modeling and molecular simulation. The GNR can spontaneously wind onto the CNT due to van der Waals (vdW) interaction and form two basic configurations: helix and scroll. The f..

Mechanics of rolling of nanoribbon on tube and sphere

The configuration of graphene nano-ribbon (GNR) assembly on carbon nanotube (CNT) and sphere is studied through theoretical modeling and molecular simulation. The GNR can spontaneously wind onto the CNT due to van der Waals (vdW) interaction and form two basic configurations: helix and scroll. The final configuration arises from the competition among three energy terms: the bending energy of the GNR, the vdW interaction between GNR and CNT, the vdW between the GNR itself. We derive analytical solutions by accounting for the three energy parts, with which we draw phase diagrams and predict the final configuration (helix or scroll) based on the selected parameters. The molecular simulations are conducted to verify the model with the results agree well with the model predicted. Our work can be used to actively control and transfer the tube-like nanoparticles and viruses as well as to assemble ribbon-like nanomaterials

A generalization of the Coulomb's friction law: From graphene to macroscale

At the nanoscale, differently to what happens at the macroscale, friction even without an applied normal pressure and spontaneous adhesion take place. In particular, the nanotribology between two layers of graphene, or other two-dimensional nanomaterials (even curved, such as nanotube walls), remains controversial. It is sufficient to say that friction between two graphene layers or nanotube walls is described in the current literature giving as "material property" a constant friction force or a constant friction shear strength, even if such views are obviously mutually exclusive. Is friction dominated by a strength, by a force or by an energy? Coupling elasticity and energy balance we solve this paradox deriving a generalization of the celebrated Coulomb's friction law, reconciling the two current views. Molecular dynamics simulations on graphene are conducted to verify its validity at the nanoscale whereas statistical simulations confirm its validity even at the macroscale

Tunable rigidity of (polymeric core)-(lipid shell) nanoparticles for regulated cellular uptake

Core-shell nanoparticles (NPs) with lipid shells and varying water content and rigidity but with the same chemical composition, size, and surface properties are assembled using a microfluidic platform. Rigidity can dramatically alter the cellular uptake efficiency, with more-rigid NPs able to pass more easily through cell membranes. The mechanism accounting for this rigidity-dependent cellular uptake is revealed through atomistic-level simulations.</p