I am using comsol to model a capillary behavior of water in an unmodified PMMA microchannel. In literature, I have seen untreated PMMA called hydrophobic. This makes no sense to me because, since its reported contact angle is 68deg, by definition it should be hydrophilic (less than 90deg) and exhibit capillary action in microchannels.
So why is PMMA considered hydrophobic in microfluidics if its contact angle is less than 90deg?
The reported behavior of untreated PMMA microfluidic devices is a lack of capillary action in microchannels. This is why there is a vast array of methods to treat PMMA and make it hydrophilic, thus enabling the capillary action in microchannels. If its contact angle is 68deg, shouldn't water move by capillary action in the untreated PMMA microchannel (thus being hydrophilic, not hydrophobic)? My model shows this exact thing when a wetted wall boundary condition of 68deg is set.
My only conclusion is that somehow the contact angle is no longer 68deg in an untreated PMMA microchannel. If so, how does this work?
