It is my opinion that linear rheology oscillatory measurements performed with AFM may not be suitable for all viscoelastic materials/solids... whereas, different is the 'story' when performing stress-relaxation measurements with AFM... such as those reported in the following two articles:
(1) https://www.nature.com/articles/s41598-018-32704-8
(2) Article Model‐Free Rheo‐AFM Probes the Viscoelasticity of Tunable DN...
Dear Manlio
The main functional mechanism of the AFM's
work is the electromagnetic waves,i.e., electrons, attraction/ repulsion force field,acquisition of the surface of the sample to the tip of the AFM. So if you have a sample surface is not fixed i.e., dynamically changing as a function of time,due for example a stress relation, the AFM oscillators rheology measurements might not be suitable for all viscoelastic materials. The waves acquisition might not be achieved in all cases.
Dear Khaled J. Habib thank you for the reply.
I should have formulated my (rhetorical) question more clearly... I was referring mostly to the stress/strain relationship between the applied stress (strain) and the strain (stress) response of viscooelastic materials.
In this case,one ought to fix,keep constant,the distance between the filement tip of the AFM
and the surface of the viscoelastic sample in order to detect the attraction/ repulsion of the force field due to not only the applied stress and the corresponding strain but also the relaxation of the surface.
Again the above suggestion might not be suitable for all viscoelastic materials,especially if the filement tip of the AFM touches the dynamic surface during the examination
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