Contact angles and coating film thickness

The effect of film thickness and surface preparation techniques on contact angles of water, 1-bromonaphtalene, and n-hexadecane on Teflon(R) AF 1600 polymeric surfaces is studied. It was found that contact angles of water on different thicknesses of spin-coated films ranging from 27 nm to 420 nm are essentially constant. This is due to the homogeneity and smoothness of the coating layers as shown by the scanning force microscopy of the samples. Furthermore, the contact angle measurements with these three liquids on both dip-coated and spin-coated films suggested that the film preparation technique does not affect contact angles dramatically. Interestingly, slightly higher contact angles on dip-coated surfaces were measured. It is also argued that the anomaly of the water contact angle - in the sense that the measured contact angle is much higher than the expected ideal value - is due to specific interactions between water and Teflon(R).