Contact Angle Measurements over Macro, Micro and Nano Dimensioned Systems - Drops and Bubbles in Contact with Solid Surfaces - page 25

(A) (B)

(C)

Figure 17. AFM tip opens the bulky liquid oil standing without mixing over the gel-like oil film
adherent to the substrate.

The three images, from the original colored pictures, show how, on a microscopic
level, it is possible to use the tip of an AFM scanning probe microscope as a spear
to 'open' a permanent hole in an amount of already liquid featured fluid condensed
over the previous adherent oil film. It can be seen that the very first condensed oil
film is still present below the liquid mass. This means that the microscopic liquid
amount never mixed within the previous deposited nanoscopic oil film. Being this
fluid not polar and neither chemically interactive with the metallic solid surface the
observed behavior has to be related to different densities of the oil molecules in the
two steric conditions.

I. Conclusions
Nano dimensioned wetting evaluations are showing their great importance in dis-
covering the effective liquid solid interactions to which macroscopic fluid displace-
ments seems to be ascribed. This dependency, already theoretically postulated, is
nowadays able to be experimentally observed. YE still holds its theoretical mean-
ing at condition to be correctly applied without misleading simplifications.

J. References

1. Young, T., Philos. Trans. R. Soc., London, 95 (1805) 65.
2. Zisman, W. A., in: Contact Angle, Wettability and Adhesion. F. M. Fowkes, Ed., Advances in
Chemistry Series, 43, 1-15. American Chemical Society, Washington, 1964.