Dear Colleagues,

I am familiar with contact angle measurments with "normal" low viscosity liquids (including time dendent phenomena) as decades ago I dealt with the surface recovery process in silicone rubber insulations after corona treatment or surface discharge exposure.

I wonder, however, if it is possible to get any information from measuring contact angles using visco-elastic polymer solutions on polymer (or other solid) surfaces? I imagine, that the problems are mulitple:

- the equilbirium (advancing) contact angle will not develop instantanously due to the viscoleastic properties of the wetting liquid (this problem may be further compounded by the inevitable surface roughness and/or the energetic heterogeneity of the surface leading to contact angle hysteresis with "normal", low viscosity liquids)

- the polymer component of the wetting liquid may adsorb to the surface, thus the contact angle may become time dependent for one more reason

- due to the extended time the evaporation of the solvent may cause further problems (which may be partly prevented by using saturted vapor environmet in the test chamber)

Provided that these obstacles are removed, is it possible to get any information on the energetic intercation between the wetted surface and the wetting polymer solution?

Is there any rule of thumb what is the practical viscosity limit where still meaningful contact angle mesurements can be made with viscous or viscoleastic solutions?

If meaningful tests can be made only after considerable dilution of the wetting solution, is there any way to extrapolate back the result for the higher concentrations?

Lookig forward to hearing the opinions of colleagues who have practical experience in such measurements. I tried to look for background literature but I did not quite found what I have been looking for.