AN ELLIPSOMETRIC STUDY OF LAYERED DROPLETS

The thickness profiles of microdroplets of non-volatile liquids spread ing on smooth solid surfaces have been studied by spatially resolved e llipsometric measurements. Our set-up is a polarization-modulated, sin gle-wavelength ellipsometer working at the Brewster angle. The lateral resolution is 25 mum, the thickness resolution is 0.2 angstrom with a time constant of 100 ms in the detection electronics. This allows one to record the drops' profiles as a function of time. The ''thick'' pa rt of these profiles (typically between 20 and 300 angstrom) is smooth . The ''thin'' part exhibits distinct molecular steps. Information on interactions and rheology at the microscopic scale can be extracted.