Imaging optical thicknesses and separation distances of phospholipid vesicles at solid surfaces

We present the application of reflection interference contrast microscopy (RICM) (1) to map the optical density of supported bilayers and vesicles and (2) to image the contact profile of phospholipid vesicles at surfaces. The resolution in the surface profile is 0.2 $\mu$m laterally and 1 nm out of plane. The optical thickness of the membrane can be determined with 0.2 nm accuracy. We outline the theoretical basis of RICM and derive the interference intensities of adhering vesicles from first principles. An analytical expression for the decaying contrast of the intrference fringes is given. The contact contour of vesicles is determined for various substrates. We further demonstrate that deposition of a magnesium fluoride layer on the glass substrate enhances the contrast and allows the optical density of adsorbed membranes to be imaged. By contrast variation of the buffer solution, the layer thicknesses and the indices of refraction can be measured. The novel method was applied to image lipid domains of different chain lengths in a substrate supported monolayer

Pattern formation in the splay Freedericks transition of a nematic side-group polysiloxane

Periodic director patterns in the magnetic-field induced splay Freedericks transition of a nematic side-group polysiloxane are reported. For this purpose liquid crystal cells (10 $\mu$m-500 $\mu$m) are studied by polarization microscopy as well as by deuteron NMR. Through this combinatin, the optically observed spatial dependence of the director can be quantitatively analyzed in terms of director distributions extracted from the NMR lineshape. In the equilibrium state of the Freedericks transition (static Freedericks effect), the director exhibits a one-dimensional periodicity perpendicular to the initial director orientation $n_{0}$. The dynamics of the Freedericks transition involves a transient two-dimensional director pattern, representing convection rolls in which the nonlinear coupling between director rotation and viscous flow of the nematic (back-flow) leads to a reduction of the viscosity