Did you know that surface roughness affects paper and board wettability? Due to their fiber-like structure, paper and board surfaces almost always have a surface with roughness. This roughness inherently affects the wettability as it amplifies the wetting effect of the surface chemistry. For hydrophilic surfaces, added surface roughness makes the surface further hydrophilic whereas with hydrophobic surfaces the effect is reversed.
Wettability therefore always consists of two components; wettability due to surface chemistry and wettability due to surface roughness. Many coating and processing methods affect both the surface chemistry and the surface roughness on a sample, making the evaluation of the coating complex. In order to fully analyze the effect of the coating, both wettability and surface roughness need to be measured at the same sample spot and the results combined to separate the effect of the roughness to the wettability.