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Published on: July 24, 2015
Wettability of graphene.
Rishi Raj1, Shalabh C Maroo, Evelyn N Wang
1Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Nano Letters
|March 6, 2013
Summary
Graphene wettability is mainly determined by surface defects, not the underlying substrate. Dynamic contact angle measurements reveal advancing angles reflect true graphene properties, while receding angles are affected by defects from growth and transfer processes.
Area of Science:
- Materials Science
- Surface Science
- Nanotechnology
Background:
- Graphene exhibits remarkable properties, yet its wettability for applications like thermo-fluidics remains poorly understood.
- Existing static contact angle studies show contradictory results, indicating a gap in understanding graphene's wetting behavior.
Purpose of the Study:
- To investigate the factors influencing graphene wettability, particularly the role of defects and substrates.
- To clarify the discrepancy in reported contact angle measurements for graphene surfaces.
Main Methods:
- Dynamic contact angle measurements on graphene sheets (mono-, bi-, trilayer) on various substrates (copper, SiO2, glass).
- Detailed graphene surface characterization to identify defects.
- Comparison with molecular dynamics simulations and theoretical calculations.
- Advancing and receding contact angle measurements were performed.
Main Results:
- Contact angle hysteresis (16-37°) was observed due to defects in chemical vapor deposition (CVD) grown and transferred graphene.
- Advancing contact angles were independent of graphene layer count and substrate, aligning with simulations and highly ordered pyrolytic graphite (HOPG) values.
- Receding contact angles were significantly influenced by intrinsic defects from growth and transfer processes.
Conclusions:
- Advancing contact angle is a reliable indicator of graphene surface wettability, unaffected by the substrate.
- Receding contact angle is sensitive to defects, providing insights into graphene quality.
- Graphene's large interlayer spacing and loose coupling with substrates minimize substrate influence on wettability, crucial for designing graphene-based coatings.
