I am conducting contact angle measurements to find the surface energy of various substrates, but when I approach them to the water droplet, the droplet bridges between the needle and the substrate before I bring them in contact. This seems like it will have a profound effect on the contact angle.
I have found some solutions such as using an ionizer or a non-polar liquid. However, I have not succeeded in removing the charge with the ionizer, and I would prefer to use water, as this is standard in similar works.
What is the best way to address these issues?
Steven Rich
Apparently, you are using AFM for research. As the tip approaches the substrate surface, proton tunneling in water occurs. It is necessary to bind a proton with a hydroxyl group. To do this, it is necessary to make the pH of the water more than 5.5. For example 7, adding ammonia and keeping it at this value. More than 8-10 is possible, but this may affect the contact angle.
Dear Dr. Steven Rich ,
the measurement of the contact angle, carried out with the "sessile drop method", is an optical technique to determine the wettability characteristics of the surface of a solid by the liquid used. The contact angle gives an indication of the relative strength of the interactions of the liquid / solid / air system.
This tool allows the evaluation of the surface wettability and the evaluation of the surface tension or free energy of the solid.
The instrument for measuring the contact angle is composed of a light source, a sample holder, a syringe for depositing a drop of liquid and an image acquisition system.
The images obtained are processed with special software, which allows you to obtain the contact angle. The contact angle value can be related to the "ease of cleaning" and the slipperiness of the surface.
In my particular case, I have always studied the characteristics of metallic material substrates and organic coatings using water as a liquid but I have never encountered the phenomenon you describe.
For more details, I suggest you to have a look at the following PhD Thesis:
Rivestimenti organici ed inorganici su substrati polimerici e metallici: analisi delle problematiche di accoppiamento all’interfaccia, individuazione di indici prestazionali e messa a punto di metodologie per la loro misura by Dr. L. Mazzola – “Roma Tre” University (2011, in Italian).
Available at: https://arcadia.sba.uniroma3.it/bitstream/2307/4548/1/Rivestimenti%20organici%20ed%20inorganici%20su%20substrati%20polimerici%20e%20metallici%20analisi%20delle%20problematic.pdf
My best regards, Pierluigi Traverso.
Dear Steven,
I agree with Prof. Yuri, changing the pH by adding amonia can simply solve your problem.
Dear Prof. Yuri Mirgorod ,
I apologize if I answered incorrectly but, in my opinion, the question was not asked very clearly. It was not my intention to propose any alternative method but only to try to understand better and give help, if possible.
I am sorry if this has not happened, at this point other different solutions proposed will be evaluated.
My best regards, Pierluigi Traverso.
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