Surface free-energy determination of copper wire using a large range of model liquids

In this paper, the surface free-energy of 700 mu m-diameter copper wires as well as its dispersive and polar components has been determined. For this, the measurement method developed for assessing advancing and receding contact angles of liquids on vertical wires has been validated with polytetrafluoroethylene (PTFE) as a well-known material.Thus, it has been checked that the dynamic contact angles of different model liquids, such as dimethylformamide, tri-cresyl phosphate or ethylene glycol, on a PTFE wire held vertically are similar to those obtained on a PTFE plane surface. Then, the Owens-Wendt approach was chosen to determine the polar and dispersive components of surface free-energy of the PTFE wire using a large range of model liquids. A surface free-energy gamma(PTFE) = 18.7 +/- 1.6 mN m(-1) was obtained with a high dispersive component, gamma(d) approximate to 17.3 +/- 1.0 mN m(-1), in comparison with the polar one, gamma(d) approximate to 1.4 +/- 0.6 mN m(-1). Using the same approach for the copper wire, a surface free-energy gamma(Cu) = 25.7 +/- 0.7 mN m (-1) was determined including mainly dispersive forces (gamma(d) approximate to 25.1 +/- 0.5 mN m(-1)).