OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 15 — Jul. 16, 2012
  • pp: 16777–16784
« Show journal navigation

Particular thermally induced phase separation of liquid crystal and poly(N-vinyl carbazole) films and its application

Yuan-Di Chen, Andy Ying-Guey Fuh, and Ko-Ting Cheng  »View Author Affiliations


Optics Express, Vol. 20, Issue 15, pp. 16777-16784 (2012)
http://dx.doi.org/10.1364/OE.20.016777


View Full Text Article

Acrobat PDF (2091 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

In the current study, a method of particular thermally induced phase separation (TIPS) of liquid crystals (LCs) and polymers is presented. The method involves a combination of dissolution process and TIPS. The LCs and poly(N-vinyl carbazole) (PVK) play the roles of solvent and solute, respectively, during the processes of particular TIPS. The nematic LC sample fabricated by two substrates coated with uniform PVK films is heated and then cooled, generating the rough PVK layers onto the surfaces of the substrates. The LC sample having rough PVK layers produces micron-sized, multiple domains of disordered LCs that can scatter incident light. Additionally, an application of a scattering mode light shutter, having the advantages of low driving voltage, polarization-independent scattering, fast response, high contrast ratio, and being polarizer free, is reported.

© 2012 OSA

1. Introduction

In the present study, the reported phase separation approach can be used to produce a rough PVK film that “re-aligns” LCs into multiple and micron-sized LC domains. The fabrication involves using disordered LC alignment based on thermally treated double-sided PVK films (no rubbing treatment). Two main mechanisms of scattering for such a light shutter exist, namely, surface scattering and volume scattering [18

18. C. Amra, “From light scattering to the microstructure of thin-film multilayers,” Appl. Opt. 32(28), 5481–5491 (1993). [CrossRef] [PubMed]

, 19

19. A. Duparré and S. Kassam, “Relation between light scattering and the microstructure of optical thin films,” Appl. Opt. 32(28), 5475–5480 (1993). [CrossRef] [PubMed]

]. Surface scattering is produced by the interface roughness between LC and the rough PVK surfaces, whereas volume scattering is caused by an inhomogeneous change in refractive index induced by the disordered LC alignment (multi-domains). The domain size generated determines the scattering performance [20

20. L. Dierking, L. L. Kosbar, A. A. Ardakani, A. C. Lowe, and G. A. Held, “Two-stage switching behavior of polymer stabilized cholesteric textures,” J. Appl. Phys. 81(7), 3007–3014 (1997). [CrossRef]

, 21

21. I. I. Kim, B. McArthur, and E. Korevaar, “Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications,” Proc. SPIE 4214, 26–37 (2001). [CrossRef]

]. Moreover, the demonstrated electrically controllable LC light shutter in the scattering mode has the advantages of low driving voltage, fast response, being polarizer free, and high contrast ratio, indicating its extremely promising potential applications. The electro-optical properties of the light shutter and the morphologies of the PVK layers are examined in detail.

2. Experiments

The chemical structures of the materials used in this study are shown in Fig. 1
Fig. 1 Chemical structures of compounds used in this paper. (a) nematic LCs (K15), and (b) photoconductive polymer (PVK).
. The nematic LC material [Fig. 1(a)] used in the current work was K15 (no = 1.5309, clearing temperature TC = ~35 °C), purchased from Merck. The photoconductive polymer [Fig. 1(b)] was PVK (nPVK = 1.68), purchased from Aldrich. The fabrication processes are different from those of conventional PDLCs sample as described above. A solution of chlorobenzene solvent with PVK at a weight ratio of 98.36:1.64 was prepared to coat the PVK (powder) film onto indium-tin-oxide (ITO)-coated glass slides. The solution was then spin-coated onto the ITO-coated glass slides. The substrates were pre-baked in an oven at 80 °C for 20 min, and post-baked at 120 °C for 120 min after coating. The thickness of the fabricated PVK film, no mechanical rubbing, was measured to be of sub-micrometer (~0.2 μm) order using the Alpha-Step IQ Surface Profiler (KLA-Tencor). Moreover, two non-rubbed PVK-coated glass substrates were combined to fabricate an empty cell, whose cell gap was 6 μm. Finally, the nematic LC (K15) was homogeneously filled into the empty cell, and the edges of the cell were sealed with epoxy to produce a sample. The fabricated LC sample was very stable at room temperature (~25 °C). The details of the proposed particular TIPS are described later.

3. Results and discussion

Figure 2
Fig. 2 Variations in stable transmission in relation to the temperature during heating (black dots) and cooling (red squares) of the LC sample fabricated from two non-rubbed PVK-coated glass substrates. The LC sample at 25 °C; (a) before (transparent) and, (b) after (scattering) thermal treatment via the particular TIPS.
shows the plot of the variation in transmittance with the temperature of an LC (K15) sample fabricated from two non-rubbed PVK-coated ITO glass substrates. Experimentally, a red probed laser beam derived from a He-Ne laser (λ = 632.8 nm) was normally incident onto the temperature-controlled LC sample. The transmitted light was collected by a photo-detector placed behind the LC sample. The high transmittance remained almost unchanged when the LC sample was gradually heated (black dots) from 25 °C to 60 °C at a heating rate of ~5 °C/min. The temperature of the LC sample was maintained at 60 °C for 8 min to dissolve PVK homogeneously, which was experimentally optimized. Subsequently, the LC sample was cooled (red squares) to 25 °C at a cooling rate of ~5 °C/min. The transmittance abruptly dropped at approximately 34 °C during the cooling process. This point is close to the clearing temperature (~35 °C) of the used LCs (K15), given that the LC phase is transformed from isotropic to nematic at this temperature. The transparent sample became a scattering (opaque) sample after thermal treatment via the particular TIPS processes. Notably, the small variations in transmittance are caused by the temperature-dependent refractive indexes of LCs and the thermal disturbance [9

9. S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).

, 22

22. J. Li, S. Gauza, and S. T. Wu, “Temperature effect on liquid crystal refractive indices,” J. Appl. Phys. 96(1), 19–24 (2004). [CrossRef]

]. The switching temperature (TS), which is defined as the temperature required to switch the LC sample from the transparent to the scattering mode, depends on the selected LCs. Experimentally, the TS of the three kinds of nematic LCs, K15 (Merck), E7 (Fusol material), and MDA-00-3461 (Merck), were ~35, ~61, and ~92 °C, respectively. TS was almost equal to the clearing temperatures, suggesting that the LC sample should be heated to a temperature higher than the clearing temperature and then cooled to generate disordered LC alignment. The insets (a) and (b) of Fig. 2 show the photographs of the LC sample at room temperature (~25 °C) before (transparent) and after (scattering) thermal treatment via the particular TIPS, respectively. The LC sample was heated at 60 °C and then cooled at 25 °C at a rate of 5 °C/min. The scattering state of the thermally treated LC sample was also stable at room temperature (~25 °C). This finding indicated that the disordered LC alignment layer was permanent at temperatures below the clearing temperature of the LCs. Restated, the thermal stability of the LC light shutter can be improved by selection of LCs with proper clearing temperature. Notably, the thermal treatment conditions, such as switching temperature, for different LC materials will be different.

The insets (a) and (b) of Fig. 3
Fig. 3 Transmittance as a function of the polarization state of the incident light. LC sample after thermal treatment via the particular TIPS at ~25 °C observed under (a) parallel- and (b) crossed-POM. P and A are the transmission axes of the polarizer and analyzer of the POM, respectively.
show the images of the thermally treated LC sample (scattering mode) at ~25 °C under parallel- and crossed-polarized optical microscopy (POM), respectively. The multi-domains of the LCs with disordered alignments presented as different colors due to their different birefringence properties (phase retardations). The sizes of the multi-domains are measured to be in the order of micrometers. Macroscopically, light incident onto the thermally-treated LC sample with multi-domains resulting from the rough PVK layer was scattered because of the following two reasons. One was the interface roughness between LCs and PVK (surface scattering), and the other was the refractive index mismatches between the boundaries of the LC domains (volume scattering). A plot of the transmittance against the polarization of the incident light (He-Ne laser) of the multi-domain scattering region [Fig. 3] revealed that the transmittance was produced by the slight light leakage penetrating the LC sample. Experimentally, the extremely low transmittance (high scattering) was independent of the polarizations of the incident light, which suggests that the multi-domains of LC were uniformly and randomly dispersed.

According to the experiment results, the original non-rubbed PVK film fabricated by pre-baking (at 80 °C for 20 min) and post-baking (at 120 °C for 120 min) after coating onto a substrate was uniform and cannot provide any alignment anchoring to disturb the alignment of the LCs. Accordingly, the original LC samples were transparent and stable at room temperature (~25 °C), as shown in the inset (a) of Fig. 2. The coated PVK dissolved in the LCs after heating to temperatures higher than its TS, which was close to the clearing temperature. This finding indicated that the isotropic LCs dissolved the coated PVK materials at temperatures higher than TS. The temperature of the LC sample was maintained at the setting temperature for several minutes to dissolve PVK homogeneously. Subsequently, the heated LC sample was cooled to room temperature. During this cooling process, TIPS occurred [9

9. S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).

]. Notably, the dissolved polymers (PVK) in the LCs tended to diffuse toward the low-temperature sides and re-form on the substrate surface. Moreover, the effects of the setting temperature of the thermal treatment, cooling rate, and cell gap on the formation of the double-sided PVK films were also elucidated.

Three LC samples with double-sided PVK films (cell gap ~6 μm) were heated to 40, 60, and 80 °C at a heating rate of 30 °C/min to investigate the effect of the setting temperature on the formation of PVK films. The setting temperature of the LC sample was maintained for 8 min to dissolve PVK homogeneously, followed by cooling to room temperature (25 °C) at a rate of 30 °C/min. The SEM morphologies of the LC samples after thermal treatment at the setting temperatures of 40, 60, and 80 °C are shown in Figs. 4(a)
Fig. 4 SEM images of LC samples after thermal treatment with setting temperatures of (a) 40, (b) 60, and (c) 80 °C at a heating rate of 30 °C/min. The temperature of the LC sample was maintained at the setting temperature for 8 min, and then cooled to 25 °C at a cooling rate of 30 °C/min.
-4(c), respectively. The morphologies of the rough PVK film in Fig. 4(c) are denser than those in Figs. 4(a) and 4(b). This result indicated that the roughness and amount of rough PVK increased with the setting temperature. The branch-like structures of the rough PVK film also became more prominent with a higher setting temperature, probably because the PVK solubility in isotropic LCs increases with the LC temperature. A separate experiment (data not shown) revealed that the scattering performance of the LC sample shown in Fig. 4(a) was very poor. The scattering performance of the thermally treated LC sample continuously increased and became saturated at the setting temperature of ~60 °C with higher setting temperature. Optically, the measured transmittances of the LC samples in Figs. 4(b) and 4(c) were identical. These findings indicated that the setting temperature of thermal treatment is the key in the fabrication of the scattering mode LC light shutter.

In order to verify the generated rough PVK structures in the bulk of the scattering LC sample, the cross-section of the LC sample, fabricated under treatment conditions consistent with those in Figs. 4(b) and 5(a), was examined by a SEM. The cross-section SEM image, shown in Fig. 6
Fig. 6 Cross-section SEM image of the thermally treated LC sample
, clearly indicates that the rough surfaces structures of these two substrates (side-view) and the bulk structures of the thermally treated LC sample (scattering mode). Moreover, obviously, several tiny branches, crossing through the bulk of the sample (from top to bottom substrates), with diameter of ~1 μm were formed.

Figure 7
Fig. 7 Measured transmission of the fabricated scattering mode LC light shutter as a function of an applied AC (1 KHz) voltage. Insets show photographs of the LC light shutter at 25 °C with the applied AC voltages of (a) 0 and (b) 18 V.
shows the plots of the measured transmittance of the scattering mode LC light shutter [fabricated under treatment conditions consistent with those in the insets (a) and (b) of Fig. 2] as a function of an applied alternating current (AC; 1 KHz) voltage. Transmittance was defined as the ratio of the intensity of the transmitted beam through the thermally-treated LC sample to that through an empty cell, such that the transmission through an empty cell was equivalent to 100%. The required voltage to achieve maximum transmittance (~76.7%) was about 18 V. A low applied AC voltage of ~13 V was required to switch the LC light shutter from the scattering mode to 90% of its maximum transmittance. Notably, the small cell gap and the weak surface anchoring resulting from the rough PVK layers are the keys to reduce the driving voltage. Additionally, the operated voltage, which was inversely proportional to the square root of the dielectric anisotropy (Δε), can be reduced to a greater extent using LCs with higher Δε values. The contrast ratio, defined as the maximum transmittance (V = ~18 V) over the minimum transmittance (V = 0 V), of the light shutter was calculated to be 300:1. Photographs of the LC light shutter at 25 °C with applied AC voltages of 0 and 18 V are shown in the insets (a) and (b) of Fig. 7, respectively. Moreover, the LC (Δε > 0) domains became aligned along the electric field as an AC voltage was applied, leading to a reduction in the refractive index mismatch (volume scattering). Thus, the scattering mode LC light shutter can be electrically switched from the opaque to the transparent mode. Notably, the transmittance cannot reach 100% considering that the fog-like scattering (surface scattering) was caused by the refractive index mismatch between no of the selective LCs and nPVK. Accordingly, proper selection of the used LCs with no equivalent to nPVK can enhance transmittance. Theoretically, the surface scattering, resulting from the refractive index mismatch between neff (1.53~1.7) of the LCs and nPVK (1.68), should be increased with the applied voltage. According to the transmittance of the light shutter with applied AC voltages of 0 and 20V, shown in Fig. 7, the volume scattering provides the main contribution to demonstrate the electrically switchable LC light shutter. Additionally, the small hysteresis (ΔV/Vpeak = ~3.5%) was still an issue for this scattering mode light shutter. This issue is attributed to the fact that a little bit of the PVK branches crossed from one substrate to the other one, according to the cross-section SEM image (Fig. 6). The structures result in the small hysteresis. Accordingly, the small hysteresis can be decreased by reducing the thickness of PVK films.

Figure 8
Fig. 8 Dynamic response (red line, plotted on the primary axis) of fabricated scattering mode LC light shutter when an AC voltage pulse (blue line, plotted on the secondary axis) of 20 V (1 KHz) is applied.
shows the dynamic response of the fabricated scattering mode LC light shutter when an AC voltage pulse is applied. The amplitude and the frequency of the pulse are 20 V and 1 KHz, respectively. The measured rise and fall times refer to the period required to change the transmittance of the light shutter from 10% to 90% and from 90% to 10% of its maximum transmittance, respectively. The rise and fall times for the scattering mode LC light shutter were about 2.25 and 3.22 ms, respectively. Notably, the backflow effect, which increases the response time, is not observed in Fig. 8. Moreover, the inner PVK structures of the LC light shutter provide a weak surface anchoring to result in the fast orientation of LC molecules, i.e. fast response [9

9. S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).

]. However, the electrically induced carrier injection from ITO/PVK into LC should be considered because PVK is well known photo-conducting polymers for UV spectral region. According to Refs. 24

24. L. Song, W. K. Lee, and X. Wang, “AC electric field assisted photo-induced high efficiency orientational diffractive grating in nematic liquid crystals,” Opt. Express 14(6), 2197–2202 (2006). [CrossRef] [PubMed]

and 25

25. X. Sun, Y. Pei, F. Yao, J. Zhang, and C. Hou, “AC electric field assisted orientational photorefractive effect in C60-doped nematic liquid crystal,” J. Phys. D Appl. Phys. 40(11), 3348–3351 (2007). [CrossRef]

, DC field and applied voltage with low frequency but not the applied voltage with high frequency, may result in the accumulation of charge carriers inside the LC bulk, which will reduce the performance of the LC light shutter severely. In case of reduction of performance, anti-UV coatings onto the substrates can be adopted to eliminate the carrier injection, produced by PVK.

4. Conclusion

In conclusion, a particular TIPS method of LCs and polymers was presented. The method was used in the successful fabrication of a scattering mode LC light shutter from LC samples consisting of double-side PVK films. Permanent scattering resulted from the formation of multiple and micron-sized domains of disordered LCs. The fabricated LC light shutter possessed the advantages of low driving voltage, fast response in the order of milliseconds, independent of polarization, high contrast ratio (~300:1), and being polarizer free. The effects of different switching temperatures, cooling rates, and cell gaps on the formation of LC light shutter were also investigated. Moreover, the electrically switchable LC light shutter in the scattering mode had extremely promising potential applications, such as in energy-efficient smart windows and scattering mode LC displays.

Acknowledgment

The authors would like to thank the National Science Council of Taiwan for financially supporting this research under Grant No. NSC 98-2112-M-006-001-MY3 and NSC 99-2112-M-006-002-MY3. Additionally, this work is partially supported by Advanced Optoelectronic Technology Center as well.

References and links

1.

D. K. Yang, L. C. Chien, and J. W. Doane, “Cholesteric liquid crystal/polymer dispersion for haze-free light shutters,” Appl. Phys. Lett. 60(25), 3102–3104 (1992). [CrossRef]

2.

R. Bao, C. M. Liu, and D. K. Yang, “Smart bistable polymer stabilized cholesteric texture light shutter,” Appl. Phys. Express 2(11), 112401 (2009). [CrossRef]

3.

H. Ren and S. T. Wu, “Reflective reversed-mode polymer stabilized cholesteric texture light switches,” J. Appl. Phys. 92(2), 797–800 (2002). [CrossRef]

4.

S. Nersisyan, N. Tabiryan, D. M. Steeves, and B. R. Kimball, “Fabrication of liquid crystal polymer axial waveplates for UV-IR wavelengths,” Opt. Express 17(14), 11926–11934 (2009). [CrossRef] [PubMed]

5.

K. T. Cheng, C. K. Liu, C. L. Ting, and A. Y. G. Fuh, “Electrically switchable and optically rewritable reflective Fresnel zone plate in dye-doped cholesteric liquid crystals,” Opt. Express 15(21), 14078–14085 (2007). [CrossRef] [PubMed]

6.

J. W. Doane, N. A. Vaz, B. G. Wu, and S. Zumer, “Field controlled light scattering from nematic microdroplets,” Appl. Phys. Lett. 48(4), 269–271 (1986). [CrossRef]

7.

A. Y. G. Fuh and O. Caporaletti, “Polymer dispersed nematic liquid crystal films: The density ratio and polymer’s curing rate effects,” J. Appl. Phys. 66(11), 5278–5284 (1989). [CrossRef]

8.

Y. H. Lin, H. Ren, and S. T. Wu, “High contrast polymer-dispersed liquid crystal in a 90° twisted cell,” Appl. Phys. Lett. 84(20), 4083–4085 (2004). [CrossRef]

9.

S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).

10.

A. Y. G. Fuh, C. C. Chen, C. K. Liu, and K. T. Cheng, “Polarizer-free, electrically switchable and optically rewritable displays based on dye-doped polymer-dispersed liquid crystals,” Opt. Express 17(9), 7088–7094 (2009). [CrossRef] [PubMed]

11.

G. Z. Liu, D. L. Xia, W. J. Yang, and Z. Q. Huang, “The surface rubbing effect on morphologies of LC droplets and electro-optic properties of flexible PDLC films,” Sci. China, Ser. Biol. Chem. 52, 2329–2335 (2009).

12.

K. J. Yang and D. Y. Yoon, “Electro-optical characteristics of dye-doped polymer dispersed liquid crystals,” J. Ind. Eng. Chem. 17(3), 543–548 (2011). [CrossRef]

13.

A. Golemme, B. Kippelen, and N. Peyghambarian, “Highly efficient photorefractive polymer-dispersed liquid crystals,” Appl. Phys. Lett. 73(17), 2408–2410 (1998). [CrossRef]

14.

S. Y. Huang, T. C. Wung, A. Y. G. Fuh, H. C. Yeh, C. M. Ma, T. S. Mo, and C. R. Lee, “Electro- and photo-controllable spatial filter based on a liquid crystal film with a photoconductive layer,” Appl. Phys. B 97(4), 749–752 (2009). [CrossRef]

15.

C. Y. Huang, J. M. Ma, T. S. Mo, K. C. Lo, K. Y. Lo, and C. R. Lee, “All-optical and polarization-independent spatial filter based on a vertically-aligned polymer-stabilized liquid crystal film with a photoconductive layer,” Opt. Express 17(25), 22386–22392 (2009). [CrossRef] [PubMed]

16.

Y. D. Chen, A. Y. G. Fuh, C. K. Liu, and K. T. Cheng, “Radial liquid crystal alignment based on circular rubbing the substrate coated with poly(N-vinyl carbazole) film,” J. Phys. D Appl. Phys. 44(21), 215304 (2011). [CrossRef]

17.

Y. D. Chen, K. T. Cheng, C. K. Liu, and A. Y. G. Fuh, “Polarization rotators fabricated by thermally-switched liquid crystal alignments based on rubbed poly(N-vinyl carbazole) films,” Opt. Express 19(8), 7553–7558 (2011). [CrossRef] [PubMed]

18.

C. Amra, “From light scattering to the microstructure of thin-film multilayers,” Appl. Opt. 32(28), 5481–5491 (1993). [CrossRef] [PubMed]

19.

A. Duparré and S. Kassam, “Relation between light scattering and the microstructure of optical thin films,” Appl. Opt. 32(28), 5475–5480 (1993). [CrossRef] [PubMed]

20.

L. Dierking, L. L. Kosbar, A. A. Ardakani, A. C. Lowe, and G. A. Held, “Two-stage switching behavior of polymer stabilized cholesteric textures,” J. Appl. Phys. 81(7), 3007–3014 (1997). [CrossRef]

21.

I. I. Kim, B. McArthur, and E. Korevaar, “Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications,” Proc. SPIE 4214, 26–37 (2001). [CrossRef]

22.

J. Li, S. Gauza, and S. T. Wu, “Temperature effect on liquid crystal refractive indices,” J. Appl. Phys. 96(1), 19–24 (2004). [CrossRef]

23.

J. M. Jin, K. Parbhakar, and L. H. Dao, “Thermally induced phase separation of a liquid crystal in a polymer under microgravity: comparison with simulations,” Langmuir 12(8), 2096–2099 (1996). [CrossRef]

24.

L. Song, W. K. Lee, and X. Wang, “AC electric field assisted photo-induced high efficiency orientational diffractive grating in nematic liquid crystals,” Opt. Express 14(6), 2197–2202 (2006). [CrossRef] [PubMed]

25.

X. Sun, Y. Pei, F. Yao, J. Zhang, and C. Hou, “AC electric field assisted orientational photorefractive effect in C60-doped nematic liquid crystal,” J. Phys. D Appl. Phys. 40(11), 3348–3351 (2007). [CrossRef]

OCIS Codes
(160.3710) Materials : Liquid crystals
(160.5470) Materials : Polymers
(230.0230) Optical devices : Optical devices

ToC Category:
Optical Devices

History
Original Manuscript: May 14, 2012
Revised Manuscript: June 27, 2012
Manuscript Accepted: June 29, 2012
Published: July 10, 2012

Citation
Yuan-Di Chen, Andy Ying-Guey Fuh, and Ko-Ting Cheng, "Particular thermally induced phase separation of liquid crystal and poly(N-vinyl carbazole) films and its application," Opt. Express 20, 16777-16784 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-15-16777


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. D. K. Yang, L. C. Chien, and J. W. Doane, “Cholesteric liquid crystal/polymer dispersion for haze-free light shutters,” Appl. Phys. Lett.60(25), 3102–3104 (1992). [CrossRef]
  2. R. Bao, C. M. Liu, and D. K. Yang, “Smart bistable polymer stabilized cholesteric texture light shutter,” Appl. Phys. Express2(11), 112401 (2009). [CrossRef]
  3. H. Ren and S. T. Wu, “Reflective reversed-mode polymer stabilized cholesteric texture light switches,” J. Appl. Phys.92(2), 797–800 (2002). [CrossRef]
  4. S. Nersisyan, N. Tabiryan, D. M. Steeves, and B. R. Kimball, “Fabrication of liquid crystal polymer axial waveplates for UV-IR wavelengths,” Opt. Express17(14), 11926–11934 (2009). [CrossRef] [PubMed]
  5. K. T. Cheng, C. K. Liu, C. L. Ting, and A. Y. G. Fuh, “Electrically switchable and optically rewritable reflective Fresnel zone plate in dye-doped cholesteric liquid crystals,” Opt. Express15(21), 14078–14085 (2007). [CrossRef] [PubMed]
  6. J. W. Doane, N. A. Vaz, B. G. Wu, and S. Zumer, “Field controlled light scattering from nematic microdroplets,” Appl. Phys. Lett.48(4), 269–271 (1986). [CrossRef]
  7. A. Y. G. Fuh and O. Caporaletti, “Polymer dispersed nematic liquid crystal films: The density ratio and polymer’s curing rate effects,” J. Appl. Phys.66(11), 5278–5284 (1989). [CrossRef]
  8. Y. H. Lin, H. Ren, and S. T. Wu, “High contrast polymer-dispersed liquid crystal in a 90° twisted cell,” Appl. Phys. Lett.84(20), 4083–4085 (2004). [CrossRef]
  9. S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays (Wiley, New York, 2001).
  10. A. Y. G. Fuh, C. C. Chen, C. K. Liu, and K. T. Cheng, “Polarizer-free, electrically switchable and optically rewritable displays based on dye-doped polymer-dispersed liquid crystals,” Opt. Express17(9), 7088–7094 (2009). [CrossRef] [PubMed]
  11. G. Z. Liu, D. L. Xia, W. J. Yang, and Z. Q. Huang, “The surface rubbing effect on morphologies of LC droplets and electro-optic properties of flexible PDLC films,” Sci. China, Ser. Biol. Chem.52, 2329–2335 (2009).
  12. K. J. Yang and D. Y. Yoon, “Electro-optical characteristics of dye-doped polymer dispersed liquid crystals,” J. Ind. Eng. Chem.17(3), 543–548 (2011). [CrossRef]
  13. A. Golemme, B. Kippelen, and N. Peyghambarian, “Highly efficient photorefractive polymer-dispersed liquid crystals,” Appl. Phys. Lett.73(17), 2408–2410 (1998). [CrossRef]
  14. S. Y. Huang, T. C. Wung, A. Y. G. Fuh, H. C. Yeh, C. M. Ma, T. S. Mo, and C. R. Lee, “Electro- and photo-controllable spatial filter based on a liquid crystal film with a photoconductive layer,” Appl. Phys. B97(4), 749–752 (2009). [CrossRef]
  15. C. Y. Huang, J. M. Ma, T. S. Mo, K. C. Lo, K. Y. Lo, and C. R. Lee, “All-optical and polarization-independent spatial filter based on a vertically-aligned polymer-stabilized liquid crystal film with a photoconductive layer,” Opt. Express17(25), 22386–22392 (2009). [CrossRef] [PubMed]
  16. Y. D. Chen, A. Y. G. Fuh, C. K. Liu, and K. T. Cheng, “Radial liquid crystal alignment based on circular rubbing the substrate coated with poly(N-vinyl carbazole) film,” J. Phys. D Appl. Phys.44(21), 215304 (2011). [CrossRef]
  17. Y. D. Chen, K. T. Cheng, C. K. Liu, and A. Y. G. Fuh, “Polarization rotators fabricated by thermally-switched liquid crystal alignments based on rubbed poly(N-vinyl carbazole) films,” Opt. Express19(8), 7553–7558 (2011). [CrossRef] [PubMed]
  18. C. Amra, “From light scattering to the microstructure of thin-film multilayers,” Appl. Opt.32(28), 5481–5491 (1993). [CrossRef] [PubMed]
  19. A. Duparré and S. Kassam, “Relation between light scattering and the microstructure of optical thin films,” Appl. Opt.32(28), 5475–5480 (1993). [CrossRef] [PubMed]
  20. L. Dierking, L. L. Kosbar, A. A. Ardakani, A. C. Lowe, and G. A. Held, “Two-stage switching behavior of polymer stabilized cholesteric textures,” J. Appl. Phys.81(7), 3007–3014 (1997). [CrossRef]
  21. I. I. Kim, B. McArthur, and E. Korevaar, “Comparison of laser beam propagation at 785 nm and 1550 nm in fog and haze for optical wireless communications,” Proc. SPIE4214, 26–37 (2001). [CrossRef]
  22. J. Li, S. Gauza, and S. T. Wu, “Temperature effect on liquid crystal refractive indices,” J. Appl. Phys.96(1), 19–24 (2004). [CrossRef]
  23. J. M. Jin, K. Parbhakar, and L. H. Dao, “Thermally induced phase separation of a liquid crystal in a polymer under microgravity: comparison with simulations,” Langmuir12(8), 2096–2099 (1996). [CrossRef]
  24. L. Song, W. K. Lee, and X. Wang, “AC electric field assisted photo-induced high efficiency orientational diffractive grating in nematic liquid crystals,” Opt. Express14(6), 2197–2202 (2006). [CrossRef] [PubMed]
  25. X. Sun, Y. Pei, F. Yao, J. Zhang, and C. Hou, “AC electric field assisted orientational photorefractive effect in C60-doped nematic liquid crystal,” J. Phys. D Appl. Phys.40(11), 3348–3351 (2007). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited