Dear Experts,
Contact angles close to advancing or receding angles are not thermodynamically stable and may relax to the most stable angle during vibrations. Relaxation of the contact angle implies that the contact area of the liquid drop on the solid's surface should relax as well.
How does this relaxation of contact angle and contact area go, simultaneously or not? Do you have any references documenting this effect?
Another question, how to describe the kinetics of relaxation, can I assume exponential relaxation vs. time?
Best regards,
Alexander
Hello Alex,
you might look in the references of Abraham Marmur or in the ones of myself.
Yes, this is a highly interesting topic.
Effects of surface inhomogeneities (both topographic and chemical) influence the movement of the drop onto the surface (I guess that is what you mean with relax). Hence drops with sufficient size have enough “stored energy” (or get “enough” by the vibration) to overcome a number of activation states so that the most stable CA can be achieved.
For smaller drops pinning and other correlations due to the surface tension strongly influences the procedure. Concerning the kinetic of the relaxation/ the movement I am convinced that common CA anaylsis procedures (software) are insufficient.
We made some progress in opening up the possibility to transfer the coordinates of the “sub”pixels of drop meniscuses in radii of curvature (we made some observations that this is the way “energy is stored”). Unfortunately, the opinion of major parts of the community seems to be that statistically/analytically based procedures like HPDSA are not practical at the moment (or even at all). It would be better (?) to “trust own students”, some coders (who wrote the code before the separation of two well-known companies), known scientist or even …
Hello Michael,
Thank you for your reply! I could not understand from your answer if the contact angle and the contact area could relax simultaneously during vibrations. Furthermore, what are the exact references?
I have a reference to simultaneous relaxation of contact area and contact angle during evaporation of a water drop (e.g., “Evaporation of droplets on strongly and weakly pinning surfaces and dynamics of the triple line,” by Bormashenko et al., 2011)
Do you know if this simultaneous relaxation is taking place during vibrations?
Best regards,
Alexander
Dear Alexander, among the many variables involved, I think viscosity plays an important role. If the viscosity is high, the vibration energy will be dissipated (the vibration will be damped). Not sure if this approximates to the answer you are looking for, more specific details of the problem, would help.
Dear Juan,
I think the viscosity should affect the time of recovery. Still, it is not related to my question regarding the simultaneous recovery of contact angle and contact area.
Best regards,
Alexander
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