Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluroethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (R(q)) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150 degrees) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coatings.