We have studied the effects of confinement on the order and dynamics of the 5CB liquid crystal (LC) inside nanosized droplets of a reflection-mode holographic-polymer dispersed LC (H-PDLC) device, consisting of alternating LC nanodroplets and polymer layers, forming a diffraction grating. Here we have investigated, taking advantage the high sensitivity of the EPR spin probe technique, a series of temperatures spanning the nematic and isotropic phase of the LC. The occurrence of phase separation and the consequent formation of a diffraction grating was revealed by SEM images of the HPDLC cross section and by the presence of a reflection peak around 565 nm. Differently from the case of BL038 LC based H-PDLCs, the results here indicate the absence of an ordered fraction of mesogens throughout the analysed temperature range. Taking into account a previous model of LC molecules arrangement in the same kind of device [Bacchiocchi, C., et al. (2009). J. Phys. Chem. B 113, 5391], we postulate the presence of very small droplets in which the surface anchoring constraints represent the dominant effect. This results in the hindrance of the LC uniform macroscopic alignment, providing a plausible explanation for the malfunctioning of these devices.

EPR study of order and dynamics of the 5CB liquid crystal in an H-PDLC device

BACCHIOCCHI, CORRADO;MIGLIOLI, ISABELLA;ARCIONI, ALBERTO;ZANNONI, CLAUDIO
2012

Abstract

We have studied the effects of confinement on the order and dynamics of the 5CB liquid crystal (LC) inside nanosized droplets of a reflection-mode holographic-polymer dispersed LC (H-PDLC) device, consisting of alternating LC nanodroplets and polymer layers, forming a diffraction grating. Here we have investigated, taking advantage the high sensitivity of the EPR spin probe technique, a series of temperatures spanning the nematic and isotropic phase of the LC. The occurrence of phase separation and the consequent formation of a diffraction grating was revealed by SEM images of the HPDLC cross section and by the presence of a reflection peak around 565 nm. Differently from the case of BL038 LC based H-PDLCs, the results here indicate the absence of an ordered fraction of mesogens throughout the analysed temperature range. Taking into account a previous model of LC molecules arrangement in the same kind of device [Bacchiocchi, C., et al. (2009). J. Phys. Chem. B 113, 5391], we postulate the presence of very small droplets in which the surface anchoring constraints represent the dominant effect. This results in the hindrance of the LC uniform macroscopic alignment, providing a plausible explanation for the malfunctioning of these devices.
C. Bacchiocchi; I.Miglioli; A. Arcioni; K. Rai; A. Fontecchio; C. Zannoni
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/121260
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