Ahesion is more or less straightforward if we want to glue together tow metarials. Peeling test works if one of the substrates is flexible. The physical picture is more or less clear. But how can one handle soft/soft surfaces e.g. between rubber and thermoplastic? There is no inteded adhesive layer, but there is some adhesion. If we want to move the two surcfaces against each other, we will experience resistance which depends on the medium, on the chemical composition of both components, on interfacial stress, complicated further by rate effects (stress relaxation etc.). The situation is even more complicated in biological systems. Here simple concepts as work of adesion (hysteresis), peeling etc. do not work. What are the best characterization techniques?
When we divide the mechanisms behind the sticking to two like; physical and chemical and then by thinking their sub-classes, it will be easier to analyze.
Chemical adhesion is irreversible in its own nature so separating two parts will definitely end-up with the fracture. It can be easily detected with solid NMR of a sample (as small as possible) from the interface, which will clearly show the changes of the chemical structure of the both surfaces and new arriving peaks as well. There is a small chance for ATR-FTIR if the there is not too much residue on the departed surfaces.
On the other hand, Physical adhesion is more tricky than the chemical ones. I will expect roughly three different mechanism for it.
Fist one is will be due to inter-molecular forces between two surface which will be easier to depart and even if there remains a residue the techniques above will definitely prove its true nature. The second will be sourced from the entanglement of the long molecular chains. It will be more powerful with respect to the adhesion caused by inter-molecular forces. To differ them from each other, a SEM image of the cross-sectional area can be very useful. The complexity and the distribution of surfaces will be the parameters to decide. I guess the weak point of this technique will be preparation of the cross-sectional area sample.
The last one which i do not have to much about is the pressure difference between the adhesion section and external space. My only guess is it will depend on how the pressure difference has arisen.
Most of above you already know but I hope it would be helpful.
Best Regards.
I know Dr. Gyorgi himself has explained some phenomena of importance. and Dr. Karem added to it. I like to add some more. The physical adhesion has one subclass which is mechanical interlocking. Every surface in microscale are uneven which help in mechanically interlock. Further, when two gels are attached with each other physically, if some force is applies or by placement it occurs. Adhesion test by using 180 degree pull may give you some idea.
Adhesion is a chemical interaction. Tack is a subjective phenomenon. Friction is a physical interaction determined by surface roughness and load (amongst other factors). I think what you are actually eluding to is TRIBOLOGY - the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear.
Hope this helps!
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