Page 37 - Plastics News May 2019

FEATURES

other 2D materials) have excited the tribology community nanoparticles have a much greater surface area per unit
because the excellent tribological properties of these mass compared with larger particles. As growth and
materials lower friction to superlubric regimes. This catalytic chemical reactions occur at surfaces, this means
opens the real possibility of creating atomically thin solid that a given mass of material in nanoparticulate form will
lubricants. be much more reactive than the same mass of material
made up of larger particles. In tandem with surface-area
A recent review (Advanced Functional Materials,
"Nanomaterials in Superlubricity") provides a status of effects, quantum effects can begin to dominate the
the progress achieved to date in using nanomaterials properties of matter as size is reduced to the nanoscale.
for achieving superlubricity. The authors beging with a These can affect the optical, electrical and magnetic
brief introduction of the role and use of nanostructured behavior of materials, particularly as the structure or
materials in superlubricity and their potential applications. particle size approaches the smaller end of the nanoscale.
Then they discuss in detail experimental and simulation Materials that exploit these effects include quantum
works on the different spatial structures of nanomaterials dots, and quantum well lasers for optoelectronics. This
associated with size effects ranging from 0D to 3D class includes nanotubes, nanorods, and nanowires. In
nanostructures. They conclude with perspectives on two-dimensional (2D) nanomaterials, two dimensions
the challenges and future directions for developing are outside the nanoscale. This class exhibits plate-like
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and nanocoatings. Three-dimensional (3D) nanomaterials
The review is structured in major sections around the DUH PDWHULDOV WKDW DUH QRW FRQÀQHG WR WKH QDQRVFDOH
dimensionality of nanomaterials – 0D, 1D, 2D and 2D. Each in any dimension. This class can contain bulk powders,
section discusses recent achievements for both solid and dispersions of nanoparticles, bundles of nanowires, and
liquid superlubricity for this class of nanomaterials. nanotubes as well as multi-nanolayers.)

7KH FODVVLÀFDWLRQ LQ ' ' ' DQG ' QDQRPDWHULDOV LV The authors conclude that an explosive progress of
based on the number of dimensions of a material, which superlubricity has been achieved in nanomaterials:
are outside the nanoscale (<100 nm) range. Accordingly,
in zero-dimensional (0D) nanomaterials all the dimensions 0D nanomaterials including C60, carbon quantum dots,
are measured within the nanoscale (no dimensions are Sb nanoparticles, nanodiamonds, nanoscrolls and onion-
larger than 100 nm). Most commonly, 0D nanomaterials like carbon effectively promote the superlubric state
are nanoparticles. In one-dimensional (1D) nanomaterials, due to their size effects that can result in the transition
one dimension is outside the nanoscale. from commensurate contact to incommensurate contact
within the local interface. Carbon nanotubes have
proven to be one effective type of 1D nanomaterials for
enhanced superlow friction at both the nanoscale and the
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and low interfacial stiffness caused by weak interplane
interactions, these 1D carbon-based nanostructures would
be good candidates for the implementation of practical
superlubric applications.
The intrinsic lubricating property of 2D nanomaterials
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heterostructures enabled them of desired low-friction
behaviors. The development of novel 3D-nanostructured
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graphitic-like amorphous carbon/MoS2 composite coatings
opened up a new path to the design of nanostructures with
superlubricity at high stress and strain levels.

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