Hello, I conducted an experiment to measure the surface free energy, or critical surface tension, of four different surfaces.
Surface Measured Literature values
Clean glass 23.8 mN/m 28 mN/m
Silanized glass 18.7 mN/m 24 mN/m
Teflon 14.8 mN/m 18.5 mN/m
Polystyrene 25.3 mN/m 33 mN/m
For the polystyrene surface, a polystyrene solution was made. It was then placed on a glass slide and spun with a spin processor to help it spread out and form a film. Methanol solutions of various concentrations were placed on each surface and the contact angles were found. Using the Zisman plot method, the surface energies for each surface were estimated to be the above values. The literature values have been listed next to them.
Although the measured values are quite different from the literature values, they follow the same trend. I'm not concerned with the difference between the values. What I don't understand is,
Why does polystyrene have a higher surface energy than the other surfaces? it appeared to be the 2nd most hydrophobic, and Teflon was the first most hyrdophobic (largest contact angle). Yet, teflon has the smallest surface energy and polystyrene has the largest. Shouldn't polystyrene have the second lowest surface energy? (My understanding was that the higher contact angle indicated a lower surface energy).
From my graphs, I can see that the change in contact angle with changing methanol concentration for polystyrene is much more significant than Teflon, which doesnt change much at all. From this, I can see why my polystyrene surface energy is calculated to be much larger. But why does this significant change occur for polystyrene and not for teflon or the other surfaces?
Can someone explain to me why polystyrene has a higher surface energy than the others? I have a feeling the reason is beyond my understanding.
Thank you.
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Topic: Surface free energy, polystyrene, teflon, silanized glass. (Read 12025 times)