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The grating formation dynamics, morphology and electro-optical properties of transmission gratings of holographic polymer dispersed liquid crystals (HPDLCs) were investigated based on partial fluorination of the host polymer matrices by incorporating three different types of fluorinated monomer. Addition and increasing amounts of fluorinated monomer gave short saturation time and increased off-state diffraction efficiency with a maximum due to the chemical incompatibility between fluorinated compounds and LC, whereas the droplet size increased with increasing fluorinated monomer content. In addition, fluorinated monomer induced decreased switching voltage and increased response time due to the low anchoring energy at the polymer-LC interfaces and increased droplet size. At an optimum content of fluorinated monomer, a minimum switching voltage of 5 V µm-1, a rise time of 0.25 ms and a decay time of 23.15 ms were obtained. [ABSTRACT FROM AUTHOR]

Chiral dopants were added to the formulation of holographic polymer-dispersed liquid crystals and the effects studied in terms of grating formation dynamics, morphology, diffraction efficiency, contrast ratio and electro-optical properties of the films. A gradual increase of real-time diffraction efficiency, decrease of droplet size and increase of diffraction efficiency of the composite film were obtained with the addition and increasing content of chiral dopant, due to the increased viscosity of the liquid crystal (LC) doped with the chiral dopant leading to decreased droplet coalescence. The contrast ratio decreased with increasing content of chiral dopant due to the difficult orientation of LC molecules caused by the formation of a helical structure. Addition of a small amount of the chiral dopant increased the driving voltage slightly, whereas the decay time is decreased significantly as a result of the high twisting of the helical structure. [ABSTRACT FROM AUTHOR]

The effects of an azo dye on the diffraction efficiency, morphology and electro-optic properties of the transmission mode of a holographic polymer dispersed liquid crystal (LC) have been studied. The azo dye induced an induction period which otherwise does not exist, followed by a gradual increase of the diffraction efficiency to a saturation value which increased with increasing azo dye content, as a result of the azo dye reorientating LC molecules within the droplet. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of the LC by the dye molecules, and to LC orientation induced by azo dye molecules giving a high refractive index contrast. The droplet size decreased with increasing dye content. The dye also lowered the threshold voltage due to the high dielectric anisotropy caused by the presence of a strong on-axis dipole moment and decreased the response time. [ABSTRACT FROM AUTHOR]