Lube-Tech
On smooth surfaces the adhesion of the drops is not affected by the concentration of the oleophobic layer, whereas on rough surfaces the efficiency of the oleophobic layer decreases with the concentration. But whatever the concentration of the oleophobic layer, the adhesion of droplets on rough surfaces is twice as high as on smooth surfaces.
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.117 page 5
Figure 11. Test specimen prepared for creeping barrier effect
Figure 10. Influence of drop volume on transit factor
In Figure 10 the influence of drop volume and concentration of oleophobic layers on the transit factor of silicone oil on glass (smooth surface) is given. With reducing the drop volumes from 1µl to 0.2µl the transit factors raise by a factor of 3.5.
Another quite interesting aspect of using oleophobic layers is to apply them as a creeping barrier for fluids. Here considerable volumes of fluids can be hindered to step onto coated surfaces. In the test array of the APG a silicone oil drop of 1.5µl was set exactly on the uncoated glass surface at the borderline to the coated area (Figure 11). When determining the transit factors, higher values are observed compared to tests when placing the droplets directly onto the oleophobic layer. Additionally a strong influence of the concentration of the coating can be observed (Figure 12): higher concentrations give higher barrier effect.
34 LUBE MAGAZINE NO.146 AUGUST 2018
Figure 12. Influence of concentration of olephobic layer on transit factor
On the surfaces of plastic materials the adhesion of lubricants is quite different. Each base material and olephobic coating concentration acts specifically with the respective lubricants. Trends may be observed, but each combination shows individual behaviour. So, for example, for each lubricant type used with a certain plastic material the optimum concentration of the oleophobic layer can be determined having the highest adhesion. The transit factors of tests with a high concentration of oleophobic layer (10) and a medium concentration of oleophobic layer (200) examples are given in Figures 13 and 14.
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