I deposited thin film of conducting polyaniline film (ES) on a microscopic glass slide, but it absorbs moisture ones it is brought out of the oven. I tried to deposit it again after depositing Cu in between, but still hygroscopic though not as in bare glass substrate. Please can anyone help.
PAni is always hygroscopic, the smaller the counter-ion, the mor hygroscopic it is. Also PAni powder absorbs a significant amount of water (10 ... 20%, I forgot the exact number).
Are you using PAni "doped" with HCl? - this would be the worst ... (in every aspect, not only hygroscopic properties).
re Cu deposition, see below next answer
re Cu:
I did not really understand what you mean with "depositing Cu in between", can you clarify? (did you deposit Cu on glass first, then PAni on Cu?)
Please be aware, that PAni is nicely reaction with Cu: when depositing PAni on Cu, PAni (originally green) will turn yellow (becomes reduced, Cu will be oxidized to Cu(+)), then with the influence of oxygen and water PAni will be re-oxidized again back to the green emeraldine salt form, BUT or AND:
PAni will have formed a strong complex with Cu(+), 1 Cu(+) ion per 12 Aniline units.
see Article New Insight into Organic Metal Polyaniline Morphology and Structure
Because now the PAni structure is different, its hygroscopy tendency is different = less strong.
one more comment below
why is PAni hygroscopic?
because the counterions do not completely "fill" the space in the chain (for structure scheme see link cited above) AND the 10 nm small primary particles adsorb water around their outer surface, building a "bridge" between the primary particles which results in higher electrical conductivity.
(really dry PAni is significantly less conductive than PAni with 10 ... 20% water adsorbed)
Dear Prof Bernhard Wessling,
Thank you so much for the answers.
Actually, I used camphor sulfonic acid not HCl. I am also going to use p-Toluene sulfonic acid.
Yes, I deposited Cu film first then followed by the polyaniline.
So now, please is there any way to modify the Polyaniline film to less or non hygroscopic one? Because, I want to use the film as a sensing layer. And part of the requirements is insensitivity to moisture.
Thank you so much.
At least you used Camphorsulfonic acid which is ok, p-toluene sulfonic acid is even better, but in any case, you will have certain (significant) amount of water be adsorbed, due to the facts which I had mentioned.
I had not explained why water will be adsorbed on the surface of the PAni 10 nm small primary particles:
- PAni has an extremely high surface tension (MUCH higher than water) as you can find here:
Data Can Conductive Polymers be truely soluble? or will they form...
- any material with any level of surface tension will adsorb materials from the surrounding environment which will reduce the surface tension (that is thermodynamically understandable as every material wants to lower the surface energy
- with water absorbed on the particle surface, PAni's surface energy is lower.
This will help you, because:
Therefore, once you equilibrated your layer in ambient atmosphere (say, in an atmosphere with about 50% relative humidity), the sensor's answers will not be sensitive upon humidity, as the amount of water adsorbed is not dependant upon the humidity in the environment but only upon the total amount of PAni (primary particles' surface), and this aount of water will be stable.
Thank you so much Prof Bernhard Wessling for the clarifications. I really appreciates your kind efforts and assistance. Thank you so much ones again.
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