An official website of the United States government
Abstract Recent advances in 2D nanomaterials, such as graphene, transition metal dichalcogenides, boron nitride, MXenes, allow not only to discover several new nanoscale phenomena but also to address the scientific and industrial challenges associated with the design of systems with desired physical properties. One of the great challenges for mechanical systems is associated with addressing friction and wear problems in machine elements. In this review, the beneficial properties of layered 2D materials that enable the control of their tribological behavior and make them excellent candidates for efficient friction and wear reduction in dry‐running and boundary lubricated machine components are summarized. The recent studies highlighting the successful implementation of 2D structures when used as solid lubricant coatings or reinforcement phases in composites for various machine components including sliding and rolling bearings, gears, and seals are overviewed. The examples presented in the studies demonstrate the great potential for 2D materials to address the energy‐saving needs by friction and wear reduction.
more »
« less
Dynamic magnetic field alignment and polarized emission of semiconductor nanoplatelets in a liquid crystal polymer
Abstract Reconfigurable arrays of 2D nanomaterials are essential for the realization of switchable and intelligent material systems. Using liquid crystals (LCs) as a medium represents a promising approach, in principle, to enable such control. In practice, however, this approach is hampered by the difficulty of achieving stable dispersions of nanomaterials. Here, we report on good dispersions of pristine CdSe nanoplatelets (NPLs) in LCs, and reversible, rapid control of their alignment and associated anisotropic photoluminescence, using a magnetic field. We reveal that dispersion stability is greatly enhanced using polymeric, rather than small molecule, LCs and is considerably greater in the smectic phases of the resulting systems relative to the nematic phases. Aligned composites exhibit highly polarized emission that is readily manipulated by field-realignment. Such dynamic alignment of optically-active 2D nanomaterials may enable the development of programmable materials for photonic applications and the methodology can guide designs for anisotropic nanomaterial composites for a broad set of related nanomaterials.
more »
« less
- Award ID(s):
- 1720530
- PAR ID:
- 10381748
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The creatures in nature exhibit dynamic responses to environmental stimuli through their hierarchical architectures. Benefiting from gradient porous structures,Delosperma nakurenseopens its protective valves of the seed capsules when hydrated with liquid water, increasing the likelihood that seeds are dispersed under conditions favorable to germination. Here, a versatile 4D printing technology, namely liquid crystal templating‐assisted vat photopolymerization (LCT‐VPP), which can fabricate bioinspired porous structures with hygro‐responsive capabilities by utilizing photopolymerization induced phase separation (PIPS) and liquid crystals (LCs) electro‐alignment is reported. PIPS within the LCs/nanofiller composites leads to the formation of submicrometer gradient porous structures after extracting nonreactive LCs. The electric field enables the programmable alignment of LCs, which in turn elongates the porous structures and aligns nanofillers. In addition, the programmable arranged nanofillers by the templated LCs enhance the degree of deformation and thus the resulting composites exhibit high shape control accuracy, fast dynamic response, and high reliability. This study opens a perspective for designing bioinspired smart materials with the special spatial distribution of porous structures. The results reported here can give rise to various potential applications in soft robots, smart anticounterfeiting devices, flexible sensors, and ultrafiltration membrane.more » « less
-
Abstract Planar alignment of disc‐like nanomaterials is required to transfer their superior anisotropic properties from microscopic individual structures to macroscopic collective assemblies. However, such alignment by electrical or magnetic field is challenging due to their additional degrees of orientational freedom compared to that of rod‐like nanostructures. Here, the realization of planar alignment of suspended graphene sheets using a rotating magnetic field produced by a pair of small NdFeB magnets and subsequent demonstration of high optical anisotropy and potential novel device applications is reported. Compared to partially aligned sheets with a static magnetic field, planar aligned graphene suspensions exhibit a near‐perfect order parameter, much higher birefringence and anisotropic absorption/transmission. A unique feature of discotic nanomaterial assemblies is that the observed order parameter and optical property can vary from isotropic to partial and complete alignment depending on the experimental configuration. By immobilizing and patterning aligned graphene in a UV‐curable polymer resin, we further demonstrated an all‐graphene permanent display, which exhibits wide‐angle, high dark‐bright contrast in either transmission or reflection mode without any polarizing optics. The ability to control and pattern graphene orientation in all three dimensions opens up new exploration and broad device applications of graphene.more » « less
-
null (Ed.)Alignment of highly anisotropic nanomaterials in a polymer matrix can yield nanocomposites with unique mechanical and transport properties. Conventional methods of nanocomposite film fabrication are not well-suited for manufacturing composites with very high concentrations of anisotropic nanomaterials, potentially limiting the widespread implementation of these useful structures. In this work, we present a scalable approach to fabricate polymer-infiltrated nanoplatelet films (PINFs) based on flow coating and capillary rise infiltration (CaRI) and study the processing–structure–property relationship of these PINFs. We show that films with high aspect ratio (AR) gibbsite (Al (OH) 3 ) nanoplatelets (NPTs) aligned parallel to the substrate can be prepared using a flow coating process. NPTs are highly aligned with a Herman's order parameter of 0.96 and a high packing fraction >80 vol%. Such packings show significantly higher fracture toughness compared to low AR nanoparticle (NP) packings. By depositing NPTs on a polymer film and subsequently annealing the bilayer above the glass transition temperature of the polymer, polymer infiltrates into the tortuous NPT packings though capillarity. We observe larger enhancement in the modulus, hardness and scratch resistance of NPT films upon polymer infiltration compared to NP packings. The excellent mechanical properties of such films benefit from both thermally promoted oxide bridge formation between NPTs as well as polymer infiltration increasing the strength of NPT contacts. Our approach is widely applicable to highly anisotropic nanomaterials and allows the generation of mechanically robust polymer nanocomposite films for a diverse set of applications.more » « less
-
Abstract In-plane anisotropic two-dimensional (2D) materials exhibit in-plane orientation-dependent properties. The anisotropic unit cell causes these materials to show lower symmetry but more diverse physical properties than in-plane isotropic 2D materials. In addition, the artificial stacking of in-plane anisotropic 2D materials can generate new phenomena that cannot be achieved in in-plane isotropic 2D materials. In this perspective we provide an overview of representative in-plane anisotropic 2D materials and their properties, such as black phosphorus, group IV monochalcogenides, group VI transition metal dichalcogenides with 1T′ and Tdphases, and rhenium dichalcogenides. In addition, we discuss recent theoretical and experimental investigations of twistronics using in-plane anisotropic 2D materials. Both in-plane anisotropic 2D materials and their twistronics hold considerable potential for advancing the field of 2D materials, particularly in the context of orientation-dependent optoelectronic devices.more » « less
