Wettability of Metal Surfaces Affected by Paint Layer Covering

The aim of the work was to quantify the surface wettability of metallic (Fe, Al, Cu, brass) surfaces covered with sprayed paints. Wettability was determined using the contact angle hysteresis approach, where dynamic contact angles (advancing Θ(A) and receding Θ(R)) were identified with the inclined plate method. The equilibrium, Θ(Y), contact angle hysteresis, CAH = Θ(A) − Θ(R), film pressure, Π, surface free energy, γ(SV), works of adhesion, W(A), and spreading, W(S), were considered. Hydrophobic water/solid interactions were exhibited for the treated surfaces with the dispersive term contribution to γ(SV) equal to (0.66–0.69). The registered 3D surface roughness profiles allowed the surface roughness and surface heterogeneity effect on wettability to be discussed. The clean metallic surfaces turned out to be of a hydrophilic nature (Θ(Y) < 90°) with high γ(SV), heterogeneous, and rough with a large CAH. The surface covering demonstrated the parameters’ evolution, Θ(A)↑, Θ(R)↑, γ(SV)↓, W(A)↓, and W(S)↓, corresponding to the surface hydrophobization and exhibiting base substratum-specific signatures. The dimensionless roughness fluctuation coefficient, η, was linearly correlated to CAH. The CAH methodology based on the three measurable quantities, Θ(A), Θ(R), and liquid surface tension, γ(LV), can be a useful tool in surface-mediated process studies, such as lubrication, liquid coating, and thermoflow.