Effects of contact angle measuring liquids on surface free energy of materials

In this thesis, the effect of the type of contact angle measuring liquids used on the calculation of the surface free energies (or surface energies) (SFE) of materials based on the liquid drop contact angle (θ) measurement data was investigated in detail. Different types of materials with flat surfaces were used in the studies. These are glass to represent ceramic materials, aluminium and titanium to represent metallic materials, and polymethyl methacrylate (PMMA), polycarbonate (PC) and polytetrafluorethylene (PTFE) to represent polymer materials. While the polar liquids used in the contact angle measurements performed by the drop sessile method are water, glycerol, formamide and ethylene glycol, the nonpolar liquids are diiodomethane, bromonaphthalene, dodecane, decane, octane, heptane and hexane. Five different methods were used for surface free energy calculations for each material, these are: Acid-Base (or Van Oss-Chaudhury-Good) Method, Equation of State (or Neumann) Method, OWRK-Fowkes (OWRK: Owens–Wendt–Rabel– Kaelble) Method, Wu Method and Zisman Method. Then, single liquid groups were determined for Equation of State Method, double liquid groups for OWRK-Fowkes and Wu Methods, triple liquid groups for Acid-Base Method and quintuple liquid groups for Zisman Method. For example, in the Acid-Base method, 10 different triple liquid groups formed by using two polar and one nonpolar liquids are as follows: W-EG-B, W-EG-D, W-F-B, W-F-D, W-GL-D, W-GL-B, EG-GL-D, EG-F-B, W-F-HEG, W-EG-HEG, W-EG-HEP [W: Water; EG: Ethylene glycol; B: Boromonaphthalene; D: Diiodometane(or methylene iodide); F:Formamide, GL: Glycerol; HEK: Hegzane, HEP: Heptane]. Afterwards, the SFE values calculated with each liquid group of the materials used were interpreted by comparing the mean SFE value and standard deviations (SD) according to these liquid groups. In addition, the relationship between the surface roughness of the materials and the FYE energy has been examined. The most important two results obtained from this study are: (i) The free surface energies determined based on the contact angle data of the materials are directly related to the measurement/test fluids used, and the change in the test fluids can definitely and seriously affect/change the SFE value, (ii) the surface roughness of the materials and the average SFE standard deviation no logical relationship could be established between the values.