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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 15 — Jul. 28, 2014
  • pp: 18513–18518
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Effects of silica nanoparticles on electro-optical properties of polymer-stabilized liquid crystals

Che-Ju Hsu, Chih-Chin Kuo, Chia-Ding Hsieh, and Chi-Yen Huang  »View Author Affiliations


Optics Express, Vol. 22, Issue 15, pp. 18513-18518 (2014)
http://dx.doi.org/10.1364/OE.22.018513


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Abstract

We control the pretilt angle of liquid crystals (LCs) by simultaneously doping silica nanoparticles (SNs) and reactive monomers into the LC cell. Application of AC high voltage (ACHV) to the cell compels the lifting force and the facilitation of polar groups to move the SNs and monomers toward the substrate surface. Polymer networks and SNs are stabilized at the substrate surface after UV exposure, sustaining the LCs at high pretilt angles. The deposited SNs on the substrate surface increases the anchoring energy of the substrate; the dispersed SNs in the cell decrease the relaxation constant of LCs. Therefore, the response time of the high-pretilted-polymer-stabilized LC cell is decreased. The method enables the control of the LC pretilt angle over a broad range. The slow response time of the polymer-stabilized LC cell from high monomer dose can also be prevented following the addition of SNs.

© 2014 Optical Society of America

1. Introduction

Electro-optical properties of liquid crystal (LC) devices are determined by various parameters, such as cell gap, electrode structure, pretilt angle, and material properties of the LCs. Most LC alignments are realized on either homeotropic or homogeneous state by using alignment materials. However, the intermediate pretilt angle of LCs between the states is necessary to improve the threshold voltage and response time of LC devices. Therefore, the control of pretilt angle is an important issue in fabricating the devices. Several methods have been developed to control the LC pretilt angle, which include stacked alignment layers [1

1. Y. J. Lee, J. S. Gwag, Y. K. Kim, S. I. Jo, S. G. Kang, Y. R. Park, and J. H. Kim, “Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers,” Appl. Phys. Lett. 94(4), 041113 (2009). [CrossRef]

], mixing of homogeneous and homeotropic alignment materials [2

2. F. S. Yeung, J. Y. Ho, Y. W. Li, F. C. Xie, O. K. Tsui, P. Sheng, and H. S. Kwok, “Variable liquid crystal pretilt angles by nanostructured surfaces,” Appl. Phys. Lett. 88(5), 051910 (2006). [CrossRef]

,3

3. W. Y. Wu, C. C. Wang, and A. Y. G. Fuh, “Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer,” Opt. Express 16(21), 17131–17137 (2008). [CrossRef] [PubMed]

], obliquely evaporated silicon oxides on the substrate surface [4

4. T. Uchida, M. Ohgawara, and M. Wada, “SiO2 liquid crystal orientation on the surface of obliquely-evaporated silicon monoxide with homeotropic surface treatment,” Jpn. J. Appl. Phys. 19(11), 2127–2136 (1980). [CrossRef]

], competition between crest and trough regions that respectively favor the vertical and planar alignments [5

5. J. B. Kim, K. C. Kim, H. J. Ahn, B. H. Hwang, J. T. Kim, S. J. Jo, C. S. Kim, H. K. Baik, C. J. Choi, M. K. Jo, Y. S. Kim, J. S. Park, and D. Kang, “No bias pi cell using a dual alignment layer with an intermediate pretilt angle,” Appl. Phys. Lett. 91(2), 023507 (2007). [CrossRef]

], continuous variation of the pretilt angle with grooves generated by atomic force microscopy [6

6. F. K. Lee, B. Zhang, P. Sheng, H. S. Kwok, and O. K. C. Tsui, “Continuous liquid crystal pretilt control through textured substrates,” Appl. Phys. Lett. 85(23), 5556–5558 (2004). [CrossRef]

], ion beam irradiation of silicon carbide (SiC) layers of various compositions [7

7. J. B. Kim, K. C. Kim, H. J. Ahn, B. H. Hwang, D. C. Hyun, and H. K. Baik, “Variable liquid crystal pretilt angles on various compositions of alignment layers,” Appl. Phys. Lett. 90(4), 043515 (2007). [CrossRef]

], fluorinated amorphous carbon (a-C:F) film with adjustable wetting properties [8

8. H. J. Ahn, J. B. Kim, K. C. Kim, B. H. Hwang, J. T. Kim, H. K. Baik, J. S. Park, and D. Kang, “Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers,” Appl. Phys. Lett. 90(25), 253505 (2007). [CrossRef]

], and pretilt angle control by formation of a thin polymer layer near the substrate surface [9

9. V. V. Sergan, T. A. Sergan, and P. J. Bos, “Control of the molecular pretilt angle in liquid crystal devices by using a low-density localized polymer network,” Chem. Phys. Lett. 486(4-6), 123–125 (2010). [CrossRef]

].

However, the methods [1

1. Y. J. Lee, J. S. Gwag, Y. K. Kim, S. I. Jo, S. G. Kang, Y. R. Park, and J. H. Kim, “Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers,” Appl. Phys. Lett. 94(4), 041113 (2009). [CrossRef]

8

8. H. J. Ahn, J. B. Kim, K. C. Kim, B. H. Hwang, J. T. Kim, H. K. Baik, J. S. Park, and D. Kang, “Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers,” Appl. Phys. Lett. 90(25), 253505 (2007). [CrossRef]

] also possess drawbacks, such as high costs, complex manufacturing processes, and low reproducibilities. The formation of a thin polymer layer near the substrate surface effectively sustains the LCs at high pretilt angles [9

9. V. V. Sergan, T. A. Sergan, and P. J. Bos, “Control of the molecular pretilt angle in liquid crystal devices by using a low-density localized polymer network,” Chem. Phys. Lett. 486(4-6), 123–125 (2010). [CrossRef]

]; however, a high monomer concentration is required, which increases the operating voltage and the response time of LC devices based on the formed polymer networks. To avoid the problems, we demonstrate the control of pretilt angle by simultaneously doping silica nanoparticles (SNs) and reactive monomers (RMs) into the LC cell. This procedure controls the pretilt angle over a broad range more efficiently than conventional polymer stabilization (PS) [9

9. V. V. Sergan, T. A. Sergan, and P. J. Bos, “Control of the molecular pretilt angle in liquid crystal devices by using a low-density localized polymer network,” Chem. Phys. Lett. 486(4-6), 123–125 (2010). [CrossRef]

]. The demonstrated method also decreases the response time of the cell. The obtained results and possible mechanisms are discussed in this paper.

2. Experimental preparations

In this study, the empty cell is constructed with two indium–tin–oxide (ITO) glass substrates that are coated with homogeneous polyimide. The top and bottom ITO glass substrates are rubbed antiparallel; the cell used is 5 ± 0.1 μm thick. The LC mixture comprises nematic E7 (Merck), SN R812 (primary particle size, 7 nm; Degussa-Huls), reactive monomer RM257 (Merck), and a small amount of photoinitiator Iragcure 651 (Ciba Additive). E7 has been widely used in LC devices due to its large birefringence (~0.2) and wide nematic temperature range (−10°C to 59°C). RM257 with reactive double bonds at both sides has rod-like structure, which exhibits nematic phase from 70 °C to 130 °C. Similar to a nematic LC, RM257 can also be aligned in a homogeneous cell [10

10. H. Ren, S. Xu, Y. Liu, and S. T. Wu, “Switchable focus using a polymeric lenticular microlens array and a polarization rotator,” Opt. Express 21(7), 7916–7925 (2013). [CrossRef] [PubMed]

]. The LC mixture is injected into the empty cell by capillary action. The cell is subject to 1 kHz 40 V AC high voltage (ACHV) for 2 min. Subsequently, the cell is then exposed to UV light (~460 μW/cm2) under 1 kHz 40 V ACHV treatment for 20 min. The effective electric field applied to the cell is 8 V/μm. Notably, after the aforementioned processes, the physical properties of E7 may have been changed. However, we do not measured them in this experiment. The electro-optical properties of the cells are analyzed after doping with various concentrations of RM257 and R812. The deviations of the measured pretilt angles and fall times are about ±1.5° and ±0.2ms, respectively.

3. Experimental results and discussions

Pristine SN-doped LC cell

Fig. 1 (a) Substrate surface image of the pristine SN-doped LC cell after ACHV treatment. (b) Pretilt angles and fall times of the cells at various SN concentrations before and after ACHV treatment. The arrows in (b) indicate the reference axes of the obtained data.
Application of ACHV reorientates the LCs and then lifts the nanoparticles towards the substrate surface [11

11. O. P. Pishnyak, S. Tang, J. R. Kelly, S. V. Shiyanovskii, and O. D. Lavrentovich, “Levitation, lift, and bidirectional motion of colloidal particles in an electrically driven nematic liquid crystal,” Phys. Rev. Lett. 99(12), 127802 (2007). [CrossRef] [PubMed]

]. The lifting force is associated with the elastic interactions between the nanoparticles and the LC director distortion near the substrate surface. The polarity of the substrate surface traps the accumulated polar SNs on the substrate surface after switching off the applied voltage [12

12. C. Y. Huang, J. H. Chen, C. T. Hsieh, H. C. Song, Y. W. Wang, L. Horng, Y. T. Shih, and S. J. Hwang, “Effect of the polyimide concentration on the memory stability of the silica-nanoparticle-doped hybrid aligned nematic Cell,” Jpn. J. Appl. Phys. 50(2R), 021702 (2011). [CrossRef]

, 13

13. S. W. Liao, C. T. Hsieh, C. C. Kuo, and C. Y. Huang, “Voltage-assisted ion reduction in liquid crystal-silica nanoparticle dispersions,” Appl. Phys. Lett. 101(16), 161906 (2012). [CrossRef]

], stabilizing the LCs at high pretilt angles. Figure 1(a) shows the substrate surface image of a 0.3 wt% SN-doped LC cell after 40V ACHV treatment. The used cell is divided into two parts, one of which is deposited with ITO electrode and the other without electrode. In the electrode area, the tiny SN grains accumulate on the substrate surface because of the generated lifting force. Conversely, the SNs are unaffected by the lifting force in the non-electrode area; the SNs remain uniformly distributed in the LC cell, but are not accumulated on the substrate surfaces. The bottom side of Fig. 1(a) is in the periphery of the field of view of the optical microscope, therefore, the observed image is dark. Figure 1(b) illustrates the pretilt angles and fall times of the cells at various SN concentrations after 40V ACHV treatment. The fall time is the time taken for the transmittance of the cell to change from 90% to 10% under pulsed voltage excitation. Dispersed SNs decrease the relaxation time constant of LCs; however, the formed SN aggregations also impede the reorientation of LCs. Therefore, the fall time of the cell before ACHV treatment is independent of the doped SN concentration. After ACHV treatment, the pretilt angle slightly increases with SN concentration because of the increased amounts of SNs that are accumulated on the substrate surface. Furthermore, the fall time of the cell markedly decreases with increasing SN concentration after treatment, because the SN aggregations are moved to the substrate surfaces, the residual tiny SNs dispersed in the cell decrease the LC relaxation time constant [14

14. C. Y. Huang, C. C. Lai, Y. H. Tseng, Y. T. Yang, C. J. Tien, and K. Y. Lo, “Silica-nanoparticle-doped nematic display with multistable and dynamic modes,” Appl. Phys. Lett. 92(22), 221908 (2008). [CrossRef]

]. Deposition of SNs on the substrate surface also increases the anchoring energy of the substrate surface, thereby decreasing the fall time of the cell [15

15. W. Li, M. Zhu, X. Ding, B. Li, W. Hung, H. Cao, Z. Yang, and H. Yang, “Studies on electro-optical properties of polymer matrix/LC/SiO2 nanoparticles composites,” J. Appl. Polym. Sci. 111(3), 1449–1453 (2009). [CrossRef]

, 16

16. X. Nie, R. Lu, H. Xianyu, T. X. Wu, and S. Wu, “Anchoring energy and cell gap effects on liquid crystal response time,” J. Appl. Phys. 101(10), 103110 (2007). [CrossRef]

]. In this paper, the maximum SN concentration is limited at 0.9 wt% because high SN dose may create aggregations, which scatter the incident light and degrade the optical properties of the cell.

Pristine RM-doped LC cell

Fig. 2 (a) Substrate surface image of the pristine RM-doped LC cell after ACHV–UV treatment. (b) Pretilt angles and fall times of the cells at various RM concentrations before and after ACHV–UV treatment. The arrows in (b) indicate the reference axes of the obtained data.
The RMs drift to the electrode surface with the facilitation of polar groups on RMs upon application of ACHV to the pristine RM-doped LC cell [17

17. L. Lu, V. Sergan, T. Van Heugten, D. Duston, A. Bhowmik, and P. J. Bos, “Surface localized polymer aligned liquid crystal lens,” Opt. Express 21(6), 7133–7138 (2013). [CrossRef] [PubMed]

, 18

18. L. Lu, V. Sergan, and P. J. Bos, “Mechanism of electric-field-induced segregation of additives in a liquid-crystal host,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 86(5), 051706 (2012). [CrossRef] [PubMed]

]. The mechanism for this effect is that ions are associated with the RMs and cause them to drift to the substrate surfaces due to the electrostatic force. When an AC field is applied, the RMs are evenly deposited on both substrate surfaces of the cell. Under UV exposure, the RMs are polymerized to sustain the LCs at high pretilt angles. Figure 2(a) exhibits the substrate surface image of the LC cell, which is also divided into electrode and non-electrode areas. In the electrode area, the RMs are polymerized by UV exposure on the substrate surface under 40 V ACHV treatment (defined as ACHV–UV treatment), but in the non-electrode area, the RMs are polymerized without ACHV treatment. The bright electrode area indicates that the LCs in this area exhibit the higher pretilt angles than those in the non-electrode area. Notably, in Fig. 2(a), due to the used cell gap and the birefringence of E7, the cell is in the dark state when the LC pretilt angle is low. As the pretilt angle increases, the phase retardation decreases and the cell becomes bright. Therefore, the non-electrode area has the lower pretilt angle and therefore the darker image, as compared with the electrode area. Figure 2(b) displays the pretilt angles and fall times of the pristine RM-doped LC cells at various RM concentrations after 40V ACHV–UV treatment. The formed polymer networks sustain the LC at high pretilt angles. However, the polymer networks also impede the reorientation of LCs, which slows the fall time of the cell. Furthermore, high pretilt angles essentially increase the fall time of the LC device [Fig. 2(b)] based on the following equations [19

19. X. Nie, H. Xianyu, R. Lu, T. X. Wu, and S. T. Wu, “Pretilt angle effects on liquid crystal response time,” J. Disp. Tech. 3(3), 280–283 (2007). [CrossRef]

]:
τd=γ1β2K,
(1)
β=2dcos1(θpθm),
(2)
where τd is the fall time, γ1 is the rotational viscosity, K is the elastic constant, d is the cell gap, and θp and θm are the pretilt angle and the maximum tilt angle of LCs in the middle of the cell, respectively. β decreases with increasing pretilt angle; thus, the fall time of the cell increases. When the doped RM concentration is ~0.9 wt%, the pretilt angle reaches ~30° and the fall time slows to 14.6 ms, which is far above that of the cell before ACHV–UV treatment (7.4 ms). The results indicate that pretilt angles greater than 30° require high RM concentrations, which create polymer networks after polymerization and impede the reorientation of LCs. Therefore, obtaining high pretilt angles by doping RMs without significantly increasing the fall time of the cell becomes difficult. The anchoring energy of the substrate, the viscosity of the LC mixture after polymerization may also affect the response time of the cell. However, because of the complex conditions after polymerization, we do not measure them in this experiment. In Fig. 1(b), the fall time of the cell after ACHV treatment is decreased with increasing pretilt angle, but not as predicted from Eqs. (1) and (2). This is because that the doped SNs not only increase the pretilt angle, but also decrease the LC relaxation time constant and increase the anchoring energy of the substrate.

SN-RM-doped LC cell

Fig. 3 Schematic of ACHV–UV-treated SN–RM-doped LC cell.
Doped RMs markedly increase the pretilt angle of the cell. However, the formed polymer networks also impede the reorientation of LCs. Doped SNs slightly increase the pretilt angle but significantly decrease the fall time of the cell, due to the decreased relaxation time constant of LCs, and the increased anchoring energy of the substrate surface. In this experiment, we propose a method to increase the pretilt angle without significantly increasing the fall time of the cell by simultaneously doping SNs and RMs into the nematic host E7. The LC-SN-RM mixture is injected into the empty cell following ACHV–UV treatment. Figure 3 implies that SNs and RMs simultaneously move to the substrate surfaces under ACHV treatment. The LC cell is then subjected to UV exposure to polymerize the RMs into networks and stabilize the SNs at the substrate surfaces. The fabricated LC cell is expected to possess the advantages of RM- and SN-doped cells, i.e., high pretilt angle and rapid fall time.

Fig. 4 (a) Substrate surface images of the SN–RM-doped LC cells after ACHV–UV treatment. (b) Pretilt angles of the SN–RM-doped LC cells at various SN concentrations after ACHV–UV treatment.
Figure 4(a) shows the substrate surface images of the SN–RM-doped LC cells after ACHV–UV treatment, in which the SN concentration is fixed at 0.9 wt%. Results indicate that the 0.5 wt% RM-doped cell exhibits the denser SN grains on the substrate surface than the 0.7 wt% RM-doped cell. The doped SN grains are wrapped by the formed polymer structures in the 0.7 wt% RM-doped cell. The pretilt angles of SN–RM-doped LC cells after ACHV–UV treatment for various SN concentrations are shown in Fig. 4(b). Pretilt angles of the cells gradually increase with SN concentration. The 0.5 wt% RM-doped cell possesses a broad control range of the pretilt angle by varying the doped SN concentration. The result implies that the substrate surface with dense SN grains stabilizes the LCs at high pretilt angles. Comparing Figs. 2(b) and 4(b) indicate that the addition of 0.9 wt% SNs markedly increases the pretilt angle to 65° in the 0.5 wt% RM-doped LC cell.

Table 1. Measured Pretilt Angles of the LC Cells after ACHV–UV Treatment at Various SN and RM Concentrations

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Table 2. Measured Fall Times of the LC Cells after ACHV–UV Treatment at Various SN and RM Concentrations

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Tables 1 and 2 summarize the measured pretilt angles and fall times of the SN–RM-doped LC cells after ACHV–UV treatment. Comparing Tables 1 and 2 indicate that a high pretilt angle of 31° and a slow fall time of ~23 ms are obtained for a doped RM concentration of 0.9 wt%. Meanwhile, 0.9 wt% pristine SN-doped LC cell exhibits a low pretilt angle of ~11° and a rapid fall time of less than 2 ms. Simultaneously doped SNs and RMs provide the LC cell a high pretilt angle and a fast fall time, therefore, a high pretilt angle of 35° and a rapid fall time of ~18.5 ms can be obtained for co-doping 0.7 wt% RMs and 0.9 wt% SNs into the cell. The resultant fall time (18.5 ms) is less than 23 ms, which is the fall time of the 0.9 wt% pristine RM-doped LC cell. The LC cell simultaneously doped with 0.5 wt% RMs and 0.9 wt% SNs yields a high pretilt angle of 65°, which can be explained by the following mechanisms. As shown in Table 1, for the 0 wt% RM-doped cells, the pretilt angles of the cells increase with SN concentrations, because of the accumulated SNs on the substrate surface [12

12. C. Y. Huang, J. H. Chen, C. T. Hsieh, H. C. Song, Y. W. Wang, L. Horng, Y. T. Shih, and S. J. Hwang, “Effect of the polyimide concentration on the memory stability of the silica-nanoparticle-doped hybrid aligned nematic Cell,” Jpn. J. Appl. Phys. 50(2R), 021702 (2011). [CrossRef]

, 13

13. S. W. Liao, C. T. Hsieh, C. C. Kuo, and C. Y. Huang, “Voltage-assisted ion reduction in liquid crystal-silica nanoparticle dispersions,” Appl. Phys. Lett. 101(16), 161906 (2012). [CrossRef]

]. The doped RMs after ACHV-UV treatment align and stabilize the LCs, further increases the pretilt angle of the cell. Consequently, in the 0.5 wt% RM-doped cell, the pretilt angle increases significantly with SN concentrations due to the synergy effects from co-doping RMs and SNs. However, for the 0.7 wt% RM-doped cell in which the RMs are over-dosed, the accumulated SNs on the substrate surface are wrapped by the formed polymer structures, as shown in Fig. 4(a). The synergy effects from co-doping RMs and SNs is weakened. Therefore, for the 0.7 wt% RM-doped cells, the increase of the pretilt angle due to SN dose is not as obvious as the 0.5 wt% RM-doped cell. However, the residual SNs dispersed in the cell still decreases the relaxation time constant of LCs. Therefore, a pretilt angle of 35° and a rapid fall time of ~18.5 ms are obtained for co-doping 0.7 wt% RMs and 0.9 wt% SNs into the cell, in which the RM concentration is over-dosed. The rise time of the cell is not shown because of its near independence with the pretilt angle.

4. Conclusion

We effectively control the pretilt angle of LCs by simultaneously doping SNs and RMs into their cells. SNs and RMs move toward substrate surfaces with ACHV–UV treatment, and the formed polymer networks and SNs sustain the LCs at high pretilt angles. The pretilt angle of LCs can be controlled between 4° and 65°, due to the synergy effects from co-doping RMs and SNs into the cell. However, as the RMs are over-dosed, the formed polymer structures wrap the SNs accumulated on the substrate surface, the synergy effects are weakened and the pretilt angle is decreased. Nonetheless, the residual tiny SNs dispersed in the cell still decrease the relaxation time constant of the LCs. In contrast to the conventional PS method, the proposed method increases the pretilt angle of LCs by using a lesser amount of RMs, which effectively reduce the hindrance of LC reorientation by the formed polymer networks. The tiny dispersed SNs in the cell also decrease the response time of the cell. The proposed method effectively controls the pretilt angle of LCs in a broad range without significantly increasing response time of the cells. The electro-optical applications of the SN–RM-doped cell, such as transflective LC display and LC lens array are underway.

Acknowledgments

The authors would like to thank the National Science Council of Taiwan (Contract Nos. NSC 101-2112-M-018-002-MY3 and NSC 103-2811-M-018-001).

References and links

1.

Y. J. Lee, J. S. Gwag, Y. K. Kim, S. I. Jo, S. G. Kang, Y. R. Park, and J. H. Kim, “Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers,” Appl. Phys. Lett. 94(4), 041113 (2009). [CrossRef]

2.

F. S. Yeung, J. Y. Ho, Y. W. Li, F. C. Xie, O. K. Tsui, P. Sheng, and H. S. Kwok, “Variable liquid crystal pretilt angles by nanostructured surfaces,” Appl. Phys. Lett. 88(5), 051910 (2006). [CrossRef]

3.

W. Y. Wu, C. C. Wang, and A. Y. G. Fuh, “Controlling pre-tilt angles of liquid crystal using mixed polyimide alignment layer,” Opt. Express 16(21), 17131–17137 (2008). [CrossRef] [PubMed]

4.

T. Uchida, M. Ohgawara, and M. Wada, “SiO2 liquid crystal orientation on the surface of obliquely-evaporated silicon monoxide with homeotropic surface treatment,” Jpn. J. Appl. Phys. 19(11), 2127–2136 (1980). [CrossRef]

5.

J. B. Kim, K. C. Kim, H. J. Ahn, B. H. Hwang, J. T. Kim, S. J. Jo, C. S. Kim, H. K. Baik, C. J. Choi, M. K. Jo, Y. S. Kim, J. S. Park, and D. Kang, “No bias pi cell using a dual alignment layer with an intermediate pretilt angle,” Appl. Phys. Lett. 91(2), 023507 (2007). [CrossRef]

6.

F. K. Lee, B. Zhang, P. Sheng, H. S. Kwok, and O. K. C. Tsui, “Continuous liquid crystal pretilt control through textured substrates,” Appl. Phys. Lett. 85(23), 5556–5558 (2004). [CrossRef]

7.

J. B. Kim, K. C. Kim, H. J. Ahn, B. H. Hwang, D. C. Hyun, and H. K. Baik, “Variable liquid crystal pretilt angles on various compositions of alignment layers,” Appl. Phys. Lett. 90(4), 043515 (2007). [CrossRef]

8.

H. J. Ahn, J. B. Kim, K. C. Kim, B. H. Hwang, J. T. Kim, H. K. Baik, J. S. Park, and D. Kang, “Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers,” Appl. Phys. Lett. 90(25), 253505 (2007). [CrossRef]

9.

V. V. Sergan, T. A. Sergan, and P. J. Bos, “Control of the molecular pretilt angle in liquid crystal devices by using a low-density localized polymer network,” Chem. Phys. Lett. 486(4-6), 123–125 (2010). [CrossRef]

10.

H. Ren, S. Xu, Y. Liu, and S. T. Wu, “Switchable focus using a polymeric lenticular microlens array and a polarization rotator,” Opt. Express 21(7), 7916–7925 (2013). [CrossRef] [PubMed]

11.

O. P. Pishnyak, S. Tang, J. R. Kelly, S. V. Shiyanovskii, and O. D. Lavrentovich, “Levitation, lift, and bidirectional motion of colloidal particles in an electrically driven nematic liquid crystal,” Phys. Rev. Lett. 99(12), 127802 (2007). [CrossRef] [PubMed]

12.

C. Y. Huang, J. H. Chen, C. T. Hsieh, H. C. Song, Y. W. Wang, L. Horng, Y. T. Shih, and S. J. Hwang, “Effect of the polyimide concentration on the memory stability of the silica-nanoparticle-doped hybrid aligned nematic Cell,” Jpn. J. Appl. Phys. 50(2R), 021702 (2011). [CrossRef]

13.

S. W. Liao, C. T. Hsieh, C. C. Kuo, and C. Y. Huang, “Voltage-assisted ion reduction in liquid crystal-silica nanoparticle dispersions,” Appl. Phys. Lett. 101(16), 161906 (2012). [CrossRef]

14.

C. Y. Huang, C. C. Lai, Y. H. Tseng, Y. T. Yang, C. J. Tien, and K. Y. Lo, “Silica-nanoparticle-doped nematic display with multistable and dynamic modes,” Appl. Phys. Lett. 92(22), 221908 (2008). [CrossRef]

15.

W. Li, M. Zhu, X. Ding, B. Li, W. Hung, H. Cao, Z. Yang, and H. Yang, “Studies on electro-optical properties of polymer matrix/LC/SiO2 nanoparticles composites,” J. Appl. Polym. Sci. 111(3), 1449–1453 (2009). [CrossRef]

16.

X. Nie, R. Lu, H. Xianyu, T. X. Wu, and S. Wu, “Anchoring energy and cell gap effects on liquid crystal response time,” J. Appl. Phys. 101(10), 103110 (2007). [CrossRef]

17.

L. Lu, V. Sergan, T. Van Heugten, D. Duston, A. Bhowmik, and P. J. Bos, “Surface localized polymer aligned liquid crystal lens,” Opt. Express 21(6), 7133–7138 (2013). [CrossRef] [PubMed]

18.

L. Lu, V. Sergan, and P. J. Bos, “Mechanism of electric-field-induced segregation of additives in a liquid-crystal host,” Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 86(5), 051706 (2012). [CrossRef] [PubMed]

19.

X. Nie, H. Xianyu, R. Lu, T. X. Wu, and S. T. Wu, “Pretilt angle effects on liquid crystal response time,” J. Disp. Tech. 3(3), 280–283 (2007). [CrossRef]

OCIS Codes
(160.3710) Materials : Liquid crystals
(160.5470) Materials : Polymers
(160.6030) Materials : Silica
(230.2090) Optical devices : Electro-optical devices

ToC Category:
Materials

History
Original Manuscript: May 14, 2014
Revised Manuscript: June 20, 2014
Manuscript Accepted: July 16, 2014
Published: July 23, 2014

Citation
Che-Ju Hsu, Chih-Chin Kuo, Chia-Ding Hsieh, and Chi-Yen Huang, "Effects of silica nanoparticles on electro-optical properties of polymer-stabilized liquid crystals," Opt. Express 22, 18513-18518 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-15-18513


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References

  1. Y. J. Lee, J. S. Gwag, Y. K. Kim, S. I. Jo, S. G. Kang, Y. R. Park, and J. H. Kim, “Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers,” Appl. Phys. Lett.94(4), 041113 (2009). [CrossRef]
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