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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References

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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef] [PubMed]

Appl. Phys. Lett. (4)

J. W. Doane, N. A. Vaz, B. G. Wu and S. Zumer, �??Field controlled light-scattering from nematic microdroplets,�?? Appl. Phys. Lett. 48, 269-271 (1986).
[CrossRef]

S. Matsumoto, M. Houlbert, T. Hayashi, and K. Kubodera, �??Fine droplets of liquid crystals in a transparent polymer and their response to an electric field,�?? Appl. Phys. Lett, 69, 1044-1046 (1996).
[CrossRef]

H. Ren and S. T. Wu, �??Inhomogeneous nanoscale polymer-dispersed liquid crystals with gradient refractive index,�?? Appl. Phys. Lett. 81, 3537-3539 (2002).
[CrossRef]

Y. H. Lin, H. Ren, and S. T. Wu, �??High contrast polymer-dispersed liquid crystal in a 90 degrees twisted cell,�?? Appl. Phys. Lett. 84, 4083-4085 (2004).
[CrossRef]

Chem. Mater. (1)

R. Sutherland, L.V. Natarajan, V.P. Tondiglia, and T. J. Bunning, �??Bragg gratings in an acrylate polymer consisting of periodic polymer-dispersed liquid-crystal planes,�?? Chem. Mater. 5, 1533- (1993).
[CrossRef]

J. Appl. Phys. (3)

S. X. Cheng, R. K. Bai, Y. F. Zou, and C. Y. Pan, �??Electro-optical properties of polymer dispersed liquid crystal materials,�?? J. Appl. Phys, 80, 1991-1995 (1996).
[CrossRef]

L. Vicari, �??Electro-optic phase modulation by polymer dispersed liquid crystals,�?? J. Appl. Phys. 81, 6612-6615 (1997).
[CrossRef]

H. Yokoyama and H. A. Van Sprang, �??A novel method for determining the anchoring energy function at a nematic liquid crystal-wall interface from director distortions at high fields,�?? J. Appl. Phys. 57, 4520-4526 (1985).
[CrossRef]

J. Chem. Phys. (1)

D. Nwabunma, H. Chiu, and T. Kyu, �??Theoretical investigation on dynamics of photopolymerization-induced phase separation and morphology development in nematic liquid crystal/polymer mixtures,�?? J. Chem. Phys 113, 6429-6436 (2000).
[CrossRef]

Macromolecules (1)

H. M. J. Boot, J. G. Kloosterboer, C. Serbutoviez, and F. J. Touwslager, �??Polymerization-induced phase separation. 1. Conversion-phase diagrams,�?? Macromolecules 29, 7683-7689 (1996).
[CrossRef]

Mol. Cryst. Liq. Cryst. (1)

N. A. Vaz, G. W. Smith, and G. P. Montgomery, �??A light control film composed of liquid-crystal droplets dispersed in a UV-curable polymer ,�?? Mol. Cryst. Liq. Cryst. 146, 1-15 (1987).
[CrossRef]

Mol. Cryst. Liq. Cryst. Suppl. (1)

J. Cognard, �??Alignment of nematic liquid-crystals and their mixtures,�?? Mol. Cryst. Liq. Cryst. Suppl. 1, 1-77 (1982).

Phys. Rev. A (1)

S. T. Wu, �??Birefringence dispersions of liquid crystals,�?? Phys. Rev. A 33, 1270-1274 (1986).
[CrossRef] [PubMed]

Phys. Rev. E (4)

A. Mertelj, L. Spindler, and M. Copic, �??Dynamic light scattering in polymer-dispersed liquid crystals,�?? Phys. Rev. E 56, 549-553 (1997).
[CrossRef]

W. J. Chen and S. H. Chen, �??Addition polymerization in a nematic medium-effects of an anisotropic solvent in a kinetic gelation model,�?? Phys. Rev. E 52, 4549-4552 (1995).
[CrossRef]

P. I. C. Teixeira and B. M. Mulder, �??Cell dynamics model of droplet formation in polymer-dispersed liquid crystals,�?? Phys. Rev. E 53, 1805-1815 (1996).
[CrossRef]

F. Basile, F. Bloisi, L. Vicari, and F. Simoni,�??Optical-phase shift of polymer-dispersed liquid-crystals,�?? Phys. Rev. E 48, 432-438 (1993).
[CrossRef]

Phys. Rev. Lett. (1)

J. B Nephew, T. C. Nihei, and S. A. Carter, �??Reaction-induced phase separation dynamics: a polymer in a liquid crystal solvent,�?? Phys. Rev. Lett. 80, 3276-3279 (1998).
[CrossRef]

Polymer (1)

T. Kyu and H. Chiu, �??Morphology development during polymerization-induced phase separation in a polymer dispersed liquid crystals,�?? Polymer 42, 9173-9185 (2001).
[CrossRef]

Other (2)

P. S. Drzaic, Liquid Crystal Dispersions (World Scientific, Singapore, 1995), Chap. 4.

J. L. Fergason, US Patent 4,435,047 (1984).

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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