Figure 8. EDS analysis of the variations of weight percentage of C (black bars) and O (cyan bars) for laser-treated and untreated surfaces after 30 days ageing in atmospheric air. Here A11 is the relation of the treated/untreated sample prepared in ambient air at 50 mm/s scan speed, with HP polarization, A12 is the same as A11, but using the scan speed 300 mm/s. A21 is the relation for the sample prepared at 50 mm/s, with VP polarization, A22 is the same as A21 but using the scan speed 300 mm/s. A31 is the relation for the sample prepared using 50 mm/s scan speed, with CP polarization, A32 is the same as A31 but using the scan speed 300 mm/s.
Samples, prepared in gas and vacuum
Here we present the results of studies of the ageing of the samples prepared with the same laser parameters as were used in above studies but in presence of different gas media. These studies were performed inside the ‘oil-less’ Chamber #1 to exclude the possible side effects caused by combination with hydrocarbons. Our experiments with gases allow us to isolate and analyze the influence of three main components of atmospheric air (N2, O2 and CO2) on the variations of wettability. This approach also excludes or at least dramatically decreases the influence of the water vapor inevitably presented in any atmospheric conditions.
The samples were prepared in the pure gases and stored in the same gas for 2 hours to achieve the relaxation after laser treatment, and then extracted from chamber and aged in ambient air for 30 days. The results of 30 days air ageing of the samples prepared in corresponding gaseous media are presented in Fig. 9. One can see the common property of all gases except oxygen: WCA’s are mainly less than 140°, thus showing the reduced speed of transition to hydrophobic state. Only one set of samples prepared in O2 environment demonstrated similar behavior as the air prepared samples. Probably, this observation emphasizes the role of oxides as the preferable substrate for facilitating the adsorption of hydrocarbon layer on the surface of laser-textured sample.