Bianca Maria Irma Van Der Zande

Mass transport phenomena during lithographic polymerization of nematic monomers monitored with interferometry

Photopolymerization of liquid-crystalline diacrylates is a versatile tool to make optical films for liquid-crystal display (LCD) enhancement. The constant drive towards LCD’s having an improved front-of-screen performance demands optical films with properties that can be adjusted on (sub) pixel level. Birefringent films made from liquid-crystalline diacrylates allow for the required adjustment of the optical property on (sub) pixel level. In this paper we report on the composition of the acrylate mixture that results in planarly aligned nematic films usable as optical retarder in transflective LCD’s as well as the mass transport phenomena that take place during heating of a mask-exposed birefringent film of liquid-crystalline diacrylates. The mass transport phenomena are studied by interferometry as a function of temperature and time. Upon heating a pronounced surface corrugation arises from the latent image formed during the mask exposure. The surface profile largely depends on lateral feature sizes. For...

Electro-optics of metal particles: electric birefringence of gold rods

The electro-optical response of aqueous suspensions of gold rods of diameter and length of 15 and 260 nm respectively, stabilized with poly(vinylpyrrolydone) was studied by electric birefringence. The electric polarizability of gold rods was calculated from the birefringence measurements as 1/10 29 Fm 2 and corresponds to that deduced from dichroism (van der Zande ’98). This value is of the same order of magnitude as the electric polarizabilities determined for non-metallic rods of similar dimensions (length about 300 nm and axial ratio about 20) such as TMV, palygorskite, oxides, etc. However, distinct differences in the optical anisotropy and the dispersion behaviour in stationary electric fields between non-metallic and metallic rods were observed. The optical anisotropy was determined (g1/g2)/0.7, which is two orders of magnitude higher than that for non-metallic rods of similar size and form. Moreover, an unexpected oscillating dispersion behaviour of the steady-state electric birefringence effect and a slow build up of the electro-optical effect compared to the decay were observed. # 2002 Elsevier Science B.V. All rights reserved.

Novel Way for Full Characterisation of Splayed Retarders using Wentzel–Kramers–Brillouin Method

The viewing angle dependency of transmissive liquid crystal (LC) displays can be reduced by use of compensation foils (retarders) exhibiting specific optical properties such as splays or tilt gradients. Thin films with tilt gradients can be characterised using the prism coupling method. This method comprises the excitation of waveguide modes in the investigated film using the evanescent field at the base of a prism in total reflection without the requirement of an immersion liquid. The resulting reflectivity curves are simulated with the help of the Berreman method. The simulations provide insights into simpler ways to evaluate the data for thin films exhibiting a tilt gradient along the layer normal. The Wentzel–Kramers–Brillouin (WKB) method for inhomogeneous films can be applied to the full characterisation of the tilt gradient without prior knowledge of thickness and refractive indices of the film. A polymerised liquid crystal sample example was investigated and a linear gradient was found for this example.