Study of a Holographic Grating based on Dye-Doped Polymer-Ball-Type Polymer-Dispersed Liquid Crystal Films

Abstract

This study investigates the characteristics of the holographic grating formed in polymer-ball-type polymer-dispersed-liquid crystal (PBT-PDLC) films, doped with a diazo dye (G206). A dye-doped PBT-PDLC sample was fabricated, and used to write a holographic grating. Experimental results indicated that the grating had memory of the polarization of the writing beams. This polarization memory effect was inerasable if the sample was heated to the isotropic phase, and then cooled down to room temperature. Based on these observations, we believe that the memory of the grating effect does not relate to the intrinsic memory in the transmission versus applied voltage curve of PBT-PDLC films, which is thermally erasable. Rather, the effect is due to a feature of the grating, resulting from the reorientation of the liquid crystals through their interaction with the photo-induced adsorption of the doped dyes on the surface of the polymer balls.

Thermally and electrically switchable gratings based on polymer-ball-type polymer-dispersed liquid-crystal films

“…The resultsthat both the zeroth-and first-order diffraction efficiencies of the s-polarized pumped grating change periodically with the angle -are believed to be caused by the adsorbed dyes in the high-intensity regions of the interference pattern that is set up by the two writing beams. 14,15 Briefly, the photo-excited dyes in these regions diffused and then adsorbed in a direction perpendicular to the polarization and the propagation directions of the pump beam ͑s-polarized͒. The adsorbed dyes then reoriented LC molecules.…”

Holographic Polymer‐Dispersed Liquid Crystals: Materials, Formation, and Applications

“…Adding a small amount of azo dye into the PDLC materials, polarization sensitive gratings can be obtained by holography [28]. The formation of the polarization gratings is attributed to the anisotropic adsorption of the azo dyes on the surfaces of polymer walls, inducing the reorientation of the liquid crystal molecules [29]. Figure 7 shows a sharp grating contrast under an optical microscope with a polarizer parallel and perpendicular to the direction of the stripe in the grating, respectively.…”

“…Grating images observed under an optical microscope with a polarizer placed in front of the sample. The transmission axis of the polarizer is (a) parallel and (b) perpendicular to the direction of the stripes in the grating[29].…”

Stability of Optical Reorientation of Nematic Liquid Crystals Doped with Azo-Dyes in Polymer Networks

“…Recently, it has been also reported that the memory effect occurs on the polymer wall of a dye-doped polymer-dispersed liquid crystal (PDLC) [8]. The alignment of the doped PDLC with azo-dyes was found to be stable without appreciable relaxation due to surface interactions between the LC and the dye molecules at the LC droplets dispersed in the polymer matrix.…”