MORPHOLOGICAL FEATURES AND WETTABILITY OF POLYTETRAFLUOROETHYLENE SURFACE TEXTURED BY LASER ABLATION

Abstract

In this paper, the morphological features of textures with non-uniform wettability created using femtosecond laser ablation of polytetrafluoroethylene substrates have been studied. Covering the surface of polytetrafluoroethylene with microcraters in accordance with a proper design a texture in the form of periodically located microcollets could be created. The period of the location of the columns is the same over the entire surface and is selected in the range from 15 to 100 microns. In the case when the period lies within 30–100 µm, the diameter of the bars is ~ 20 µm. If in the range of 15–20 µm, then this diameter decreases accordingly to ~ 10 µm. Depending on the pulse energy, the height of the pillars could be smoothly changed from 0 to 60 μm. However, to create a superhydrophobic concentrator, textures with the greatest depth were used so that the height of the columns does not limit the stability of the superhydrophobic state by the sagging mechanism. It was established that on the surface of each pillar during the process of laser ablation, a relief with a two-modal roughness in the form of short drop-shaped projections of the material covered with spherical globules is additionally formed. Thus, in one stage of laser micromachining, it is possible to create a surface with a three-modal roughness – microcolumns, drop-shaped projections and spherical globules. The process of droplet evaporation is represented by two main modes of constant contact angle and constant contact diameter, when the latter ceases to decrease and remains constant until the complete evaporation of the drop. As a result, a precipitate of the substance dissolved in a drop is formed on the substrate. It has been established that in the interval 0 <τ <0.9, evaporation occurs in the constant contact angle mode.