Ellipsometry studies of liquid interfaces: New methodology and applications
Abstract: Adsorption of several surface active agents, such as nonionics, diblock copolymers, triblock copolymers, proteins and phospholipids at the oil/water and air/water has been studied. In order to be able to do this, a new ellipsometry setup, which utilizes light guides, was developed and tested. A new evaluation methodology was developed and tested as well. This methodology is based on performing each experiment twice, with two different substrates. The small difference in the refractive indices of these substrates will allow for resolving both the adsorbed amount and the layer thickness from deltaDelta alone, using the thin film approximation. It was also demonstrated in which way simulated ellipsometry experiments and Brewster angle microscopy (BAM) could be utilized in interpreting ellipsometry results. The influence of the viscosity of the oil phase on the adsorption kinetics of block coploymers at the oil/water interface has been investigated. Measurements suggest the formation of diffuse layers at the decane/water interface during the adsorption of nonionics such as C12E5 and C18E50. Further results show the formation of lamellar liquid crystalline phases at the oil/water interface when Phospholipids are added to the oil. These layers have been characterized using Small Angle X-ray diffraction (SAXD), ellipsometry, and BAM.
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