Fullerenes
have been recognized as good candidates for solid lubricants.
In this study, the microscale superlubricity of fullerene derivatives
was accomplished by the construction of regular host–guest
assembly structures. Herein, the host–guest assembly structures
of fullerene derivatives were successfully constructed on a highly
oriented pyrolytic graphite (HOPG) surface by introducing the macrocycles
as the templates and were explicitly revealed by scanning tunneling
microscopy (STM). Meanwhile, the nanotribological properties of the
host–guest assemblies were measured using atomic force microscopy
(AFM), revealing ultralow friction coefficients of 0.003–0.008,
which could be attributed to the restriction on removal of fullerene
molecules after introducing the templates. The interaction energies
were calculated by density functional theory (DFT) method, which indicates
the correlation between friction coefficients and interaction strength
in the host–guest assemblies. The effort on fullerene-related
superlubricity could extend the solid superlubrication systems and
provide a novel pathway to explore the friction mechanisms at the
molecular level.
materials are promising in reducing friction-induced energy loss and wear in automotive and electronics industries because of their superior tribological performance. As a kind of organic 2D materials, the structure and functionality of covalent organic frameworks (COFs) are much easier to tailor compared to other inorganic 2D materials, which expand their potential application in a Micro-Electro-Mechanical System (MEMS). In this manuscript, several kinds of COFs are synthesized and characterized on the surface of highly oriented pyrolytic graphite (HOPG) to investigate the nanotribological mechanism of organic 2D materials. It is surprisingly revealed that the friction coefficients of surface COFs are positively correlated with the pore sizes of honeycomb networks. The COFs with smaller pores would have a smoother potential energy surface and exhibit a lower friction coefficient. Besides, the porous structures of surface COFs make them good candidates to be host templates. The host−guest assembly structures are successfully constructed after introducing coronene molecules, and these host− guest systems display higher friction coefficients because the assembly structure of the guest molecules would be perturbed during the friction process and bring additional slip energy barriers, but the capacity of COFs to form composite assembly with functional guest molecules greatly promotes their further application in the MEMS.
Boron-dipyrromethenes (BODIPY) are promising functional dyes, whose exceptional optical properties are closely related to their supramolecular assembly. Herein, the self-assembly of a BODIPY derivative functionalized with uracil groups is explicitly and thoroughly investigated by using scanning tunneling microscopy (STM). Based on the simulation and calculation by density functional theory (DFT) method, it can be concluded that the construction of ordered self-assembly structure is attributed to the formation of hydrogen bonds between uracil groups. Moreover, the nanotribological property of the self-assembly on HOPG surface is measured by using atomic force microscopy (AFM). The effort on self-assembly of the BODIPY derivative could enhance the understanding of surface assembly mechanism.
Liquid crystals are promising molecular materials in the application of lubrication. Herein, the microscale solid superlubricity is accomplished by the construction of uniform and ordered self-assembly of several liquid crystals. The self-assembly structures on a highly oriented pyrolytic graphite (HOPG) surface are explicitly revealed by using scanning tunneling microscopy (STM). Meanwhile, the nanotribological performance of the self-assemblies are measured by using atomic force microscopy (AFM), revealing ultralow friction coefficients lower than 0.01. The interaction energies are calculated by density functional theory (DFT) method, indicating the positive correlation between friction coefficients and interaction strength. The effort on the self-assembly and superlubricity of liquid crystals could enhance the understanding of the nanotribological mechanism and benefit the further application of liquid crystals as lubricants.
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