Modulating the body's networks could become mainstream therapy for many health issues.
Image credit: The Feinstein Institutes for Medicine Research.
New Research In
Physical Sciences
Featured Portals
Articles by Topic
Biological Sciences
Featured Portals
Articles by Topic
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved October 31, 2019 (received for review September 26, 2019)
Significance
The functional properties of surfaces are often dictated by their wettability. For example, to minimize smudging on a surface, it should be able to repel and not be wetted by oil easily. The most common approach to quantify the surface wettability is to measure the contact angle of a droplet. While easy to perform, such measurements are crude and imprecise. Here, we report a technique to measure the interaction forces between a small microdroplet and a surface with nanonewton resolution and spatially map the local wetting properties at the micrometer scale. The insight generated by the technique can then inform future design of functional coatings.
Abstract
There is a huge interest in developing superrepellent surfaces for antifouling and heat-transfer applications. To characterize the wetting properties of such surfaces, the most common approach is to place a millimetric-sized droplet and measure its contact angles. The adhesion and friction forces can then be inferred indirectly using Furmidge’s relation. While easy to implement, contact angle measurements are semiquantitative and cannot resolve wetting variations on a surface. Here, we attach a micrometric-sized droplet to an atomic force microscope cantilever to directly measure adhesion and friction forces with nanonewton force resolutions. We spatially map the micrometer-scale wetting properties of superhydrophobic surfaces and observe the time-resolved pinning–depinning dynamics as the droplet detaches from or moves across the surface.
Footnotes
- ↵1To whom correspondence may be addressed. Email: daniel{at}imre.a-star.edu.sg.
Author contributions: D.D. designed research; D.D., C.L.L., A.S., C.J.J.L., and X.Y.L. performed research; C.L.L., D.C.J.N., and X.Y.L. contributed new reagents/analytic tools; D.D. and N.T. analyzed data; and D.D. and N.T. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
Data deposition: Data used to generate Figs. 1–5 in the main text and those in SI Appendix have been deposited in Harvard dataverse (https://doi.org/10.7910/DVN/1HWMVS). File types are csv files which can be opened by most text reader software. The python code used to numerically solve the droplet’s geometry has been deposited at https://github.com/ddaniel331/laplace_solver.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1916772116/-/DCSupplemental.
Published under the PNAS license.
Log in using your username and password
Purchase access
You may purchase access to this article. This will require you to create an account if you don't already have one.
Mapping micrometer-scale wetting properties of superhydrophobic surfaces
Sign up for Article Alerts
Article Classifications
- Physical Sciences
- Engineering
Jump to section
You May Also be Interested in
Adaptations in heart structure and function likely enabled endurance and survival in preindustrial humans.
Image courtesy of Pixabay/Skeeze.
Viscoelastic carrier fluids enhance retention of fire retardants on wildfire-prone vegetation.
Image courtesy of Jesse D. Acosta.
Water requirements may make desert bird declines more likely in a warming climate.
Image courtesy of Sean Peterson (photographer).
QnAs with NAS member and plant biologist Sheng Yang He
Image courtesy of Sheng Yang He.