Abstract

The orientational photorefractive effect was observed in an organic-inorganic nanocomposite of nematic liquid crystal hybridized with montmorillonite clay. Both the self-diffraction and beam-coupling effects were evaluated in a two-wave-mixing experiment in conjunction with an externally applied dc field. The experimental results indicate that photoinduced generation was enhanced by the addition of smectite clay with adequate concentration. Physically, the drifting ion charges were trapped by clay layers and separated by interlayer cations, creating an internal, spatially modulated space-charge field, which led to nematic molecular orientation and, then, refractive-index modulation via the electro-optical response. The diffraction efficiency as well as the beam-coupling ratio of the phase gratings recorded in the cells of the nematic liquid crystal hybridized with montmorillonite clay was found to be two to three times higher than that in the pristine nematic cell.

© 2005 Optical Society of America

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References

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Adv. Mater. (1)

R. A. Vaia, C. L. Dennis, L. V. Natarajan, V. P. Tondiglia, D. W. Tomlin, and T. J. Bunning, �??One-step, micrometer-scale organization of nano- and mesoparticles using holographic photopolymerization: A generic technique,�?? Adv. Mater. 13, 1570�??1574 (2001).
[CrossRef]

Annu. Rev. Mater. Res. (1)

G. P. Wiederrecht, �??Photorefractive liquid crystals,�?? Annu. Rev. Mater. Res. 31, 139�??169 (2001).
[CrossRef]

Appl. Phys. (1)

H. Ono and N. Kawatsuki, �??Orientational holographic grating observed in liquid crystals sandwiched with photoconductive polymer films,�?? Appl. Phys. Lett. 71, 1162�??1164 (1997).
[CrossRef]

Appl. Phys. Lett. (3)

P. Pagliusi and G. Cipparrone, �??Surface-induced photorefractive-like effect in pure liquid crystals,�?? Appl. Phys. Lett. 80, 168�??170 (2002).
[CrossRef]

H. Ono, T. Kawamura, N. M. Frias, K. Kitamura, N. Kawatsuki, and H. Norisada, �??Measurement of photorefractive phase shift in mesogenic composites,�?? Appl. Phys. Lett. 75, 3632�??3634 (1999).
[CrossRef]

W. Lee and S.-L. Yeh, �??Optical amplification in nematics doped with carbon nanotubes,�?? Appl. Phys. Lett. 79, 4488�??4490 (2001).
[CrossRef]

J. Phys. D: Appl. Phys. (1)

W. Lee and Y.-L. Wang, �??Voltage-dependent orientational photorefractivity in a planar C60-doped nematic film,�?? J. Phys. D: Appl. Phys. 35, 850�??853 (2002).
[CrossRef]

J. Phys.: Condens. Matter (1)

C. Pizzey, S. Klein, E. Leach, J. S. V. Duijneveldt, and R. M. Richardson, �??Suspensions of colloidal plates in a nematic liquid crystal: a small angle x-ray scattering study,�?? J. Phys.: Condens. Matter 16, 2479�??2495 (2004).
[CrossRef]

JETP Lett. (1)

E. V. Rudenko and A. V. Sukhov, �??Photoinduced electrical conductivity and photorefraction in a nematic liquid crystal,�?? JETP Lett. 59, 142�??146 (1994).

Mater. Sci. Eng. (1)

M. Kawasumi, N. Hasegawa, A. Usuki, and A. Okada, �??Nematic liquid crystal/clay mineral composite,�?? Mater. Sci. Eng. C6, 135�??143 (1998).

Nanotechnology (1)

Y.-P. Huang, H.-Y. Chen, W. Lee, T.-Y. Tsai, and W.-K. Chin, �??Transient behaviour of polarity-reversed current in a liquid-crystal�??montmorillonite-clay device,�?? Nanotechnology 16, 590�??594 (2005).
[CrossRef]

Opt. Lett. (3)

Proc. Ann. Technical Conf. SPE 2000 (1)

T.-.Y Tsai, C.-L. Hwang, and S.-Y. Lee, �??A fresh approach of modified clays for polymer/clay nanocomposites,�?? in Proceeding of the Annual Technical Conference 2000, Vol. II, (Society of Plastics Engineers, Orlando, FL, 2000), pp. 2412�??2415.

Solid State Commun. (1)

K. Sutter, J. Hulliger, and P. Günter, �??Photorefractive effects observed in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane,�?? Solid State Commun. 74, 867�??870 (1990).
[CrossRef]

Other (2)

R. W. Boyd, Nonlinear Optics (Academic Press, London, 1992).

L. Solymar, D. J. Webb, and A. Grunnet-Jepsen, The Physics and Applications of Photorefractive Materials (Oxford University Press, Oxford, 1996).

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Figures (6)

Fig. 1.
Fig. 1.

SEM images of montmorillonite clay. (a) Microscale clay particle formed from stacked lamellae and (b) clay particles, delaminated from microscale particles, with diameters smaller than 200 nm well-dispersed in the NLC phase.

Fig. 2.
Fig. 2.

Observed dependence of the first-order self-diffraction efficiency on the wave-mixing angle for an NLC hybridized with 1.0-wt% montmorillonite clay.

Fig. 3.
Fig. 3.

Self-diffraction pattern in the absence of one of the two incident beams.

Fig. 4.
Fig. 4.

Kinetics of diffraction efficiencies of doped and undoped E7.

Fig. 5.
Fig. 5.

Schematic illustration of PR grating formation in oriented NLC layers. (a) Charge generation, (b) charge transport and trapping, and (c) space-charge field and reorientation of LC.

Fig. 6.
Fig. 6.

Asymmetric energy exchange observed in (a) E7 and (b) E7 hybridized with 1-wt% clay.

Equations (2)

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η = ( I 1 I 1 ) × 100 %
Q = 2 π L λ n Λ 2

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