Investigation of layered microdroplets using ellipsometric techniques

Previously single wavelength ellipsometry has been successfully used to study the spreading of liquid polymer microdroplets on solid substrates. Extending that experimental approach, we present in this study the first experiments of spatially resolved spectroscopic ellipsometry applied to the spreading of layered microdroplets and show that it is possible to recover the experimental thickness profiles of polydimethylsiloxane and squalane on hydrophilic silicon wafers. To complement these molecular measurements, we also present new computer simulation results concerning the velocity field and the mass transfer during this spreading process. These results are in agreement with the predictions of the de Gennes-Cazabat model. (C) 1998 Elsevier Science S.A.