I've used Atomic Force Microscopy PF-QNM mode to study changes of my crystalline material in high humidity conditions. During time the surface is changing and I see round clusters appearing on the surface. Clusters have lower adhesion force values that my material. There are two possibilities, either (A) my material undergoes some kind of solid-solid transition (probably to hydrated form of my material), or (B) the water condenses on the surface and the round clusters are actually some kind of surface solution.
So if the clusters have lower adhesion which scenario (A or B) is more plausible?
And the second question is :can I directly relate the adhesion to surface energy? So can I say that the clusters that I see have lower surface energy than my crystalline material? Or is that I bit too big statement. This paper below relates adhesion with surface energy, but condition that they have had is 0 % RH to avoid any additional capilarry forces, but I I'm using 70% RH, so I'm not sure if this conclusion would be still relevant.
http://link.springer.com/article/10.1007/s11095-005-9144-1
Thanks in advance for any useful comments :)
Hi Monika
The cluster you see can certainly by explained by a dissolution-precipitation process ; this is usually observed when you have a water meniscus between the tip and the surface ; you dissolved away from the tip and you reprecipitate under the tip since you applied a certain pressure on the surface. I have already published this on a gypsum surface.
Concerning the surface energy, do not forget that the adhesion force that you measure depend both on the surface radius of the tip , but also on the surface , and the cluster you are looking at are not flat. So small cluster can lead to low adhesion forces but il does not mean that the surface energy or surface tension is lower
Hope this will help you
Eric
Hi Eric, Hi Anurag,
Thanks a lot for your suggestions.
I think Eric's suggestion about inducing some precipitation/crystallisation by the tip make sense. I have also had a look at the gypsum paper.
My material is hydrophobic and it slightly dissolves in water. Hydrated form of this material is also known. Clusters are around 50-150 nm in diameter and 20-80 nm high. Hope you can see the image that I have attached (results from 70% RH). So the adhesion value in between clusters is higher comparing to just a pure material itself (before placing it in 70% RH). This could suggest water condensed on the surface in 70% RH? The adhesion on the clusters is slightly lower comparing to pure material (so that could suggest maybe hydrated/different form crystallising out?).
Thanks.
Monika! Adhesion forces greatly depend on the radius of curvature of the specimen surface. Therefore, strictly speaking, even with the same chemical composition and structure of the surface under study they can be compared only to the surface regions with the same curvature. We faced this problem in the study of the effect of nanoparticles in the biopolymer matrix of the adhesive forces. My question is whether it is possible to propose a universal method of comparing the forces of adhesion on materials with different surface curvature and different composition?
Hi Monika
We published some research about this. I hope you can find some information there.
Best
Thanks everyone for all the suggestions! Thanks Pedro for suggesting the paper.
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