Diffusion kinetics of formation of holographic polymer-dispersed liquid crystal display materials

Abstract

The underlying physical phenomena behind the increased reflection/diffraction efficiency of holographically formed polymer-dispersed liquid crystal gratings formed from blended oligomers are investigated. Using parameters determined by in situ diffraction measurements during grating formation, a phenomenological diffusion model shows that a composition modulation in the polymer network results in blended oligomer systems. Scanning electron microscope studies reveal polymer morphologies consistent with this hypothesis.

Effects of Monomer Functionality on Switchable Holographic Gratings Formed in Polymer‐Dispersed Liquid‐Crystal Cells

“…The overall changes occurring in the grating morphology, observed in the present work as a function of functionality, are in good qualitative agreement with results published previously for different HPDLC systems, in the sense that a well-defined periodic grating structure is formed only in HPDLC mixtures containing monomers of sufficiently high functionalities. [40][41][42][43][44] …”

“…Our choice of low laser intensity was based on the intuition that the polymerization and diffusion rates in effect at such low curing intensities should result in well-defined and "cleaner" morphology of the gratings. Whereas Bowley et al [41] and Sarkar et al [43] utilized an aliphatic urethane acrylate system cured with an Ar + laser, Park et al [42] studied a novel system containing polyurethane acrylates. As Park and Kim have shown, although the diffraction efficiency increases monotonically with irradiation intensity (100 < I < 250 mW cm À2 ), it is the film composition which produces an optimum diffraction efficiency at a particular value, and the microstructure of the grating depends on the functionality of the acrylate monomers.…”

“…[40] Other important results have been published on similar but significantly different systems. [41][42][43][44] Because of the differences…”

Tunable pattern transitions in a liquid-crystal-monomer mixture using two-photon polymerization

“…Composited by spreading submicrometer-sized liquid crystal (LC) droplets in a polymer matrix, PDLCs have shown both electrical and optical tunabilities, and have been applied to a variety of applications in optical devices from light switches, phase modulators, holographic gratings, to flat panel displays. Depending on the profile of writing beam and interplay among photoinduced polymerization, phase separation morphologies, and diffusion mechanism of monomer molecules, different structures like gratings, waveguides, and broken stripes are demonstrated [2][3][4][5]. In comparison to one-photon absorption, in recent decades, two-photon (TP) lithography has emerged as a promising technique for direct laser writing, for its capacity to fabricate fine and well formed patterns, as well as three-dimensional structures, microscaled in size and nanoscaled in resolution [6,7].…”

“…Laser beams with polarization perpendicular to the direction of writing and the alignment of liquid crystals, produce snake-shaped patterns at an intermediate scan rate [2][3][4][5]. In comparison to one-photon absorption, in recent decades, two-photon (TP) lithography has emerged as a promising technique for direct laser writing, for its capacity to fabricate fine and well formed patterns, as well as three-dimensional structures, microscaled in size and nanoscaled in resolution [6,7].…”