Comment on ´Effect of surface charge on hydrophobicity levels of insulating materials´

In the paper by Moreno-Villa et al. (see ibid., vol.145, no.6, p.675-81, 1998) it has been suggested that surface charges on insulating materials have a significant influence on the hydrophobicity levels of insulating materials, especially glass, ceramic and silicone rubber. In the comment we have investigated the possible influence of surface charge on the hydrophobicity levels of different insulating materials and found that surface charges do not play any significant role in the hydrophobicity levels, contrary to the claim by Moreno-Villa et al. To isolate the possible influence of the charging method on the hydrophobicity, we used three different charging methods, namely corona discharge, plasma treatment and triboelectric charging, to deposit charges on the insulating materials. In addition to depositing charges on the insulating surfaces, the corona discharge and plasma treatment produced significant reduction in hydrophobicity. However, the triboelectric charging method deposits large amounts of charges on the insulating materials without producing any significant change in the hydrophobicity level. From these experiments it appears that the presence of surface charges is not responsible for the hydrophobicity loss in insulating materials. Corona discharge and plasma treatment are known to produce surface modifications, and perhaps it is these surface modifications that are responsible for the surface hydrophobicity loss