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.