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Pinning effect on the phase separation dynamics of thin polymer-dispersed liquid crystals

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Abstract

The surface pining effects on phase separation dynamics of polymer-dispersed liquid crystals (PDLCs) with thin cell gaps are demonstrated. Comparing various boundary conditions, the inner surfaces of the substrates with or without polyimide layers [but no rubbing] cannot provide enough anchoring force, so in either case the liquid crystal (LC) droplets flow and coalesce to form larger and less uniform droplets. However, if the inner surfaces of the substrates are coated with rubbed polyimide layers with anchoring energy >1x10-4 J/m2, almost all the nucleated LC droplets grow at a fixed position during phase separation. The appearance of the coalescence is not obvious and the formed LC droplets are relatively uniform. The surface anchoring has a significant effect on the morphology of PDLCs.

©2005 Optical Society of America

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Supplementary Material (8)

Media 1: MPG (815 KB)     
Media 2: MPG (816 KB)     
Media 3: MPG (503 KB)     
Media 4: MPG (375 KB)     
Media 5: MPG (987 KB)     
Media 6: MPG (986 KB)     
Media 7: MPG (980 KB)     
Media 8: MPG (979 KB)     

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Figures (5)

Fig. 1.
Fig. 1. Phase separation morphologies of PDLC in (a) conventional cell, (b) PI cell without rubbing, (c) TN cell (anchoring energy ~3x10-4 J/m2), (d) homogeneous cell (anchoring energy ~3x10-4 J/m2), and (e) homogeneous cell (anchoring energy ~1x10-4 J/m2) observed from a polarized optical microscope. LC/monomer mixture: 70 wt% E48 and 30 wt% NOA65. Both devices have the same cell gap d~8 µm.
Fig. 2.
Fig. 2. The dynamic phase separation morphologies of PDLC observed from a polarized optical microscope under different temperatures without UV illumination: (a) conventional PDLC cell (816KB), (b) PI without rubbing (816KB), (c) TN cell (504KB), and (d) homogeneous cell (376KB).
Fig. 3.
Fig. 3. The dynamic phase separation morphologies of PDLC at T=27 °C with UV exposure starting at t=0: (a) conventional cell without PI (986KB), and (b) PI cell without rubbing (986KB). The UV intensity is I=60 mw/cm2.
Fig. 4.
Fig. 4. The dynamic phase separation morphologies of PDLC at T=27 °C with UV exposure starting at t=0: (a) TN cell (980 KB), and (b) homogeneous cell (979 KB). The UV intensity is I=60 mw/cm2 and cell gap d=8 µm.
Fig. 5.
Fig. 5. Voltage-dependent transmittance of the 16-µm (black solid and dashed lines) and 4-µm (gray solid and dashed lines) homogeneous PDLC cells. Solid lines: the input polarization is parallel to the cell rubbing direction. Dashed lines: the input polarization is perpendicular to the rubbing direction. λ=633 nm and T=22 °C.
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