Dear reader,
when contacting a solid surface with a sessile liquid drop, a gas bubble forms depending on viscosity and momentum of contact.
What´s the physicochemical reason? Any literature?
My problem in detail: I am trying to join two glass chips (several mm edge length) with a liquid adhesive. For this I place one chip under a stereomicrosocope, dispense a drop of adhesive (ca. 30 microL, visc. 4000 mPas, degassed, UV-cure) onto it, grab the second chip with a tweezer, approach the drop vertically from atop, make gentle contact and release the second chip.
The drop initially is bubble-free, but in the moment of contact a gas bubble forms with a diameter of about 0.1mm. I tried 2K-silicone with the same viscosity: same result. I tried Polycarbonate and Polystyrene as transparent chip materials with the same outcome. I placed small droplets on both surfaces: same result. When using droplets of higher viscosity, the bubble diameter increases. I electrostatically discharged all materials.
Only reducing the approach velocity yields a bubble-free joint.
So, it´s not surface tension related (?)
What is it?
Thanx in advance, Martin