Is there a commercial source of well defined (i.e. known, reproducible surface roughness, flatness, etc.) "standard" materials that you can purchase? A perfect example would be a vendor that sells prepared surfaces that will produce contact angles of 90, 120, 150, 180 when exposed to water at known environment conditions (i.e. 21C, etc.). Thanks in advance.
Dear Dr. Michael Pujari-Palmer,
I suggest you to have a look at the following technical notes/papers, hoping that they are useful for your research:
-Contact Angle MeasurementsUsing the Drop Shape Method
by Roger P. Woodward, Ph.D.
Available at: https://www.firsttenangstroms.com/pdfdocs/CAPaper.pdf
-New drop contour standard for calibrating our Drop Shape Analyzers
Available at: https://www.kruss-scientific.com/news/newscast/article/new-drop-contour-standard-for-calibrating-our-drop-shape-analyzers/
-Construction and calibration of a goniometer to measure contact angles and calculate the surface free energy in solids with uncertainty analysis
Jonathan M. Schuster, Carlos E. Schvezov, Mario R. Rosenberger
Available at: https://arxiv.org/ftp/arxiv/papers/1810/1810.10904.pdf
-Standards for Tensiometers
By Biolin Scientific
Available at: https://www.biolinscientific.com/attension/standards-for-tensiometers
-Influence of Experimental Variables on the Measure of Contact Angle in Metals Using the Sessile Drop Method
Jonathan M. Schustera, Carlos E. Schvezov, Mario R. Rosenberger
Procedia Materials Science, 8 pages 742 - 751, (2015)
Available at: https://core.ac.uk/download/pdf/80359687.pdf
Good reading and best regards, Pierluigi Traverso.
From an instrument vendor's point of view, this is a sourcing problem. Even if you find a standard surface that will reproducibly provide a particular contact angle, you have to be extremely concerned about storage and contamination. Hydrocarbons and dust in the air will stick on low-surface energy materials. Roughness also needs to be controlled.
For contact angle instruments, vendors can provide glass slides with silhouettes of hanging droplets (surface/interfacial tension) and sessile droplets (contact angle measurements) to ensure that the drop-fitting software algorithms are properly working. Basically, the surface tension or contact angle value is known for the silhouette on the glass slide, and you measure the silhouette as if it was your sample and see if you get the correct value. This is much more important for a surface tension measurement because the size scale for each pixel matters for the surface tension calculation but not for the contact angle measurement, which involves finding the droplet, identifying the angle, and doing the geometry analysis.
If you really wanted a sample that would reproducibly give you a particular contact angle, I would recommend trying something like mica, which you would cleave before each measurement. Cleaving ensures you have a reproducible, perfectly clean surface every time. I would use a non-polar probing liquid like diiodomethane, as water would completely wet the surface and not provide a good shape. You could expect a value between 20-30 degrees for this (Contact Angle, Wettability and Adhesion, Volume 6, ed. K. L. Mittal).
Alternatively, if you wanted a hydrophobic material, you could consider sourcing a Teflon-type material, but you would have to be careful about how you cleaned it, and depending on the formulation and roughness could provide varying values.
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