Rotational diffusion and orientational fluctuations in polymer-dispersed liquid crystals

A. Mertelj; L. Spindler; Martin Copic

doi:10.1117/12.300018

1 February 1998 Rotational diffusion and orientational fluctuations in polymer-dispersed liquid crystals

A. Mertelj, L. Spindler, Martin Copic

Proceedings Volume 3318, Liquid Crystals: Physics, Technology, and Applications; (1998) https://doi.org/10.1117/12.300018
Event: Liquid Crystals, 1997, Zakopane, Poland

Abstract

Polymer dispersed liquid crystal was studied by dynamic light scattering. In the experiments where no electric field is applied the system exhibits additional slow dynamics to ne observed in bulk nematics. This slow dynamics spreads out over several decades of time and gradually disappears with increasing electric field. It can be attributed to the rotational diffusion of the liquid crystal droplets in random potential as was confirmed by model computations. The random potential is due to the irregularities in the shape of the droplets. While the measured time intensity correlation function does not depend on the scattering vector in the system where no field is applied due to the multiple scattering, its dependence in the electric field shows expected size effects. In confined systems with typical size d there are no eigenmodes of the orientational fluctuations with wave vectors less than minimal wave vector q_min equals (pi) /d. We observed quadratic dependence of the inverse relaxation time on the scattering vector down to certain scattering vector, below which the relaxation time remains constant. The size calculated form this minimal scattering vector is in agreement with the average droplet size obtained from scanning electron microscope photographs and atomic force microscope images of our sample. The electric field changes the temperature behavior of the inverse relaxation time near the nematic-isotropic phase transition which increases with the temperature when electric field is applied, but decreases when the field is absent.

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A. Mertelj, L. Spindler, and Martin Copic "Rotational diffusion and orientational fluctuations in polymer-dispersed liquid crystals", Proc. SPIE 3318, Liquid Crystals: Physics, Technology, and Applications, (1 February 1998); https://doi.org/10.1117/12.300018

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KEYWORDS

Scattering

Liquid crystals

Correlation function

Polymers

Diffusion

Light scattering

Dynamic light scattering

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