The contact angle of thin-uncured epoxy films: thickness effect

The contact angle of thin-uncured epoxy films spin casted on oxidized silica wafers has been investigated as a function of their thickness in the range of 5–75 nm. Based on the contact angle measurements with polar and apolar liquids, the surface free energy of various films were analyzed and compared using Lifshitz van der Walls/acid–base and harmonic mean (Wu’s) approaches. The results show that the nature of the surface of epoxy films change to more hydrophobic state as its thickness increases. Furthermore, time monitoring of the contact angle of the surface of epoxy films reveals a more rapid conformational change or flip–flop of surface epoxy chains for thicker layers. other hand, epoxy layer could screen out the substrate interaction for both polar and apolar liquids with a pseudo-exponential functionality on film thickness. A pseudo-exponential trend of the contact angle and surface free energy components of the films towards the values of thick films was observed.