Spatially resolved ellipsometry

During spreading, the droplets assume the shape of Aztec pyramids, like the droplet shown in Fig. 1.19. This has been observed using spatially-resolved ellipsometry. 

The spontaneous spreading of thin microdroplets on solid substrates is slow and can be conveniently monitored using spatially resolved ellipsometry. On the other hand, extended thin wetting films can be spin-coated on solids or deposited on liquid substrates and thereafter studied under a polarized microscope for nanometric thicknesses or a Brewster angle microscope for molecular ones. X-ray reflectometry provides complementary information. 

Fig. 5. Precursor film profiles obtained by spatially resolved ellipsometry on two PDMS drops of very different characteristics (1) Mii =6500, Q=1.34 10 cm, viscosity q=0.53 P., spreading time 75 hours, 0 =0.055(2) Af = 280,000, ft=6.11 lO" cm, q=24500 P., spreading time 2856 "hours, 0 =0.914 . The two profiles are cut at the transition towards the macroscopic drop. In the insert (vertical scale expanded x 2.) the dotted line is the best adjustment of the tail of (1) on the asymptotic form 2 ]/(x-Xq) with a=1 (predicted by ref. (2) and (3)), while the semi-dotted line is for a = 2.

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