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Hi everyone,
Recently I am testing the mechanical properties of polymer in water, but it has small adhesion. During adhesion, the force is complex, including adhesion force, electrostatic force and repulsion btw tip and polymer. Because the indentation is small around 3-4nm, I really need to analysis the data clearly. So I wonder how can I get rid of adhesion force during my experiment? Or it there a method to subtract it during data process? In another way, how can I determine the base line in such situation?
Thanks in advance.
Qian
You can try to "switch off" adhesion by changing the environment. Depending on the forces which lead to adhesion this could be e.g. increasing ionic strength, changing pH, or similar. Of course always be aware that this might also change the morphology on the polymer.
You can also try to coat the cantilever. If the tip is gold-coated then you can use short thiol-PEG or short thiol-alkane-PEG. You should use very short chains because they pack more densely and don't disturb the force measurements too much. Look around for publications regarding to tip passivation. If you use silicon or silicon nitride tips then you need usually additional steps to activate the substrate for binding of the PEG etc.
For algorithms that try to deal with adhesion, maybe this is helpful:
1. Lin, D. C., Dimitriadis, E. K. & Horkay, F. Robust strategies for automated AFM force curve analysis--I. Non-adhesive indentation of soft, inhomogeneous materials. Journal of biomechanical engineering 129, 430–40 (2007). http://www.ncbi.nlm.nih.gov/pubmed/175369112. Lin, D. C., Dimitriadis, E. K. & Horkay, F. Robust strategies for automated AFM force curve analysis-II: adhesion-influenced indentation of soft, elastic materials. Journal of biomechanical engineering 129, 904–12 (2007). http://www.ncbi.nlm.nih.gov/pubmed/18067395
There are also other publications with different algorithms. Whether they work depends heavily on your data.
Thanks, janne！I have another question, because my polymer has thiol group on the end, and tip I am using has back side gold coating. Is it possible they would attract each other?