Optical Microscopic Sizing of 2D Nanomaterials

Case Western Reserve University Background
Companies that synthesis and/or utilize nanomaterials typically have a quality control process that includes sizing of the nanomaterial. Although some nanomaterials, such as spherical particles, can be sized with traditional light scattering techniques, two-dimensional (2D) nanosheets cannot be characterized in this way because of the shape. Atomic Force Microscopy (AFM) can be used to size 2D nanosheets, but is both expensive and inherently slow. Scanning Electron Microscopy (SEM) can be used to size 2D nanosheets, but is very expensive and requires the nanomaterial to be in a vacuum. Further, neither AFM nor SEM are amenable to manufacturing environments as is this new in-situ measurement technique.
Technology Overview
The enabling process for this technology is one in which 2D nanosheets are prepared for imaging to allow for rapid sizing of the projected area of each particle (). By introducing the nanostructures to a liquid-liquid interface, providing probe particles to the liquid-liquid interface, obtaining an image of the nanostructures and the probe particles, and processing the image with optical microscopy, the size of the nanostructures is able to be readily determined. For instance, when imaged with an optical microscope, the 2D nanosheets appear because of outlines from the probe particles. Thus, the 2D nanosheets, which would typically not be visible with optical microscopy, become visible because of the surrounding material.
This technique is fast and economical. Current efforts to make a portable unit could reduce the cost 10X from $5,000 to $500. The process does not require careful sample preparation or special environments and is well suited to high-volume, production manufacturing environments for in-situ sizing measurement of 2D nanosheets.
Further information:
“Efficient sizing of single layer graphene oxide with optical microscopy under ambient conditions,” by Qinmo Luo, Christopher Wirth, and Emily Pentzer Carbon February 2020, v157, p395-401.

Simple and cheap hardware able to incorporate into (or add on to) existing optical microscopic instruments.
Provides for easy operation and time efficient imaging for a large number of 2D nanosheets.
The nature of the measurement itself enables high throughput measurements.

In comparison to an isolated, clean-room based AFM / SEM unit costing at least $100,000 or more, this device represents a revolutionary reduction in cost and increase in useability.
Graphene oxide (GO) is a common nanomaterial that would benefit from this simplified sizing process. The process would also be useful for additives, coatings, composites, and understanding particle interactions.

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