Surface Free Energy of Bare and Fluorinated Siloxanes: Comparing Experimental Evaluation and Dipole Moments Calculations

The surface free energy (SFE) is a key parameter in evaluating the physico-chemical features of solid surfaces. Studies on the composition, structure and interfacial phenomena of a surface layer of materials are of special importance. Its assessment allows the interpretation of several phenomena, such as adsorption mechanisms and surface wettability behaviors, occurring at solid-liquid and solid-gas interfaces; hence the knowledge of such properties is fundamental for both technological and more fundamental point of view. Here, the surface free energy of three non-fluorinated and three fluorinated siloxanes is evaluated. All siloxanes were synthesized and deposited in thick films onto a glass substrate by spin coating. Experimental static contact angle data elaborated by empirical models (Zisman, EOS, OWRK), together with theoretical dipole moment calculations and wetting envelope (WE) elaborations allow us to predict the wetting behaviors towards the most common solvents. The effect of the addition of fluorinated -CF3 end-groups in imposing the final wetting features of the siloxane films is fully investigated on the grounds of the above mentioned experimental and theoretical investigations.