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Bull. Soc. Photogr. Imag. Japan. (2016) Vol. 26 No. 2: 14–17

Original Paper

Fast Response of Liquid Crystal Devices Doped with Poly(cyclodextrin)-Stabilized ZrO2 /Ag Hybrid Nanoparticles
Yukihide Shiraishi*, Takahito Kanzaki*, Hiroya Sawai*, Hitoshi Asano*, Yukou Du** and Naoki Toshima***

Abstract:Poly (β-cyclodextrin)-stabilized zirconia/silver (PβCyD-ZrO2 /Ag) nanoparticles were prepared from colloidal dispersions of PβCyD-ZrO2 nanoparticles. Particles of PβCyD-ZrO2 /Ag(molar ratio of ZrO2 /Ag = 0.8/0.2) nanoparticles have an average diameterof 4.5 nm. The nanoparticles were dispersed in 4’-pentyl-4-cyanobiphenyl to construct liquid crystal displays. The response time ofthis display in the presence of PβCyD-ZrO2 /Ag nanoparticles was faster than that in the absence of nanoparticles.

Key words:

Liquid crystal display, Nanoparticles, Silver, Zirconia, Poly(cyclodextrin)

1. Introduction
Liquid crystal molecules have been studied as raw materials for anelectronic display device for more than three decades due to its electro-optic properties, and now constructs main parts of informationindustries. The liquid crystal displays (LCDs), however, have a disadvantage of slow response compared with electroluminescence displays. Thus, it will be a big impact to design LCDs with fast response, if liquid crystal sol containing nanomaterials may have novel
dynamic properties different from the original liquid crystal medium by giving a perturbation to a self-assemble property of liquid
crystal. The merging of nanomaterials or nanotechnology in a wide
sense into self-assembled systems such as LCDs may attract the attention of researchers who are interested in inaugurating a new kindof combination of different fields.1) In fact, the number of papers,
especially patents on a liquid crystal display concerning with nanomaterials increases rapidly these years. The nanomaterials reported
as a dispersed phase in LCDs involves fullerene,2) carbon nanotubes,3) diamond powders,4) and metal nanoparticles,5,6) etc. Whenused as a dopant for LCDs they were expected to improve the contrast, decrease the driving voltage, capture ions, and shorten the response time.
Nanoparticles have attracted a great interest in scientific researchand industrial applications, owing to their unique large surface-to-volume ratios and quantum-size effects.7) From both thescientific and technological point of view, bimetallic nanoparticles
composed of two different metal elements are more promising thanmonometallic nanoparticles, because synergistic effect is expected.8)
Bimetallic nanoparticles have shown novel catalytic behaviors basedon the effect of second metal element added. This effect of second
metal element can be often explained in terms of an ensemble and/or a ligand effect. The synthesis of bimetallic nanoparticles is mainly
divided into two methods, that is, the chemical and physical methods, or the “bottom-up” and “top-down” methods. The chemical
method involves simultaneous or coreduction, successive or twostep reduction of two kinds of metal ions, and “self-organization” ofbimetallic nanoparticles by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after
treatments. Previously, we reported 4’-pentyl-4-cyanobiphenyl(5CB)-stabilized Ag/Pd bimetallic nanoparticles by the lightirradiation of the tetrahydrofuran solution of silver(I) perchlorate andpalladium(II) acetate in the presence of a liquid crystal molecule.9)
Infrared spectra of carbon monoxide adsorbed on the bimetallic
nanoparticles suggested that bimetallic nanoparticles had a random
alloy structure.10) To the best of our knowledge, there is no reports onelectro-optic properties of liquid-crystal display doped by oxide/
metal hybrid nanoparticles.
Recently, we obtained poly (cyclodextrin)-stabilized zirconia(PCyD-ZrO2) nanoparticles by ultrasonic and microwave reactionof zirconium(IV) ethoxide in tetraethylene glycol.11) This study is
aimed to develop novel functional PβCyD-ZrO2/Ag hybrid nano­particles having high dispersibility into liquid crystal matrices. Colloidal dispersions of ZrO2/Ag hybrid nanoparticles were applied tothe electro-optic properties of LCDs.

2. Experimental
PβCyD-ZrO2 nanoparticles were prepared by using a microwave

Received: 9th, May 2016; Accepted: 1st, July 2016

*Department of Applied Chemistry, Tokyo University of Science Yamaguchi, Daigakudori, SanyoOnoda, Yamaguchi 756-0884, Japan.

**College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China***Advanced Materials Institute, Tokyo University of Science Yamaguchi, Daigakudori, SanyoOnoda, Yamaguchi 756-0884, Japan
Corresponding author. Tel: +81 836 88 4580, fax:+81 836 88 3844
Email address: shiraishi@rs.tusy.ac.jp(Y. Shiraishi)

Yukihide Shiraishi, Takahito Kanzaki, Hiroya Sawai, Hitoshi Asano, Yukou Du and Naoki Toshima

reactor equipped with ultrasonic nozzle. PβCyD (0.017 mmol inmonomeric units, 0.1 times the total amount of zirconyl chloride
octahydrate) and zirconyl chloride octahydrate (0.17 mmol) weremixed in mixture of water/tetraethylene glycol(1/16, v/v) to form a
250 cm3 solution. The mixed solutions was filled with pure nitrogen(99.999%) and then exposed to the microwave (2450 MHz) andultrasonic waves (150 W, 20 kHz) at the same time. Contaminants
like ions in the dispersions were removed by washing the dispersions
three times with ethanol by using an ultrafiltration. Complete removal of the solvent and volatile byproducts by vacuum evaporation
gave PβCyD-ZrO2 nanoparticles. The PβCyD-ZrO2 nanoparticles
prepared were used as core seeds for ZrO2-core/Ag-shell nanoparticles. The seed PβCyD-ZrO2 nanoparticles were dispersed into tetraethylene glycol in a two-necked 100-mL flask equipped with adropping funnel, which was charged with a degassed aqueous solution (50 mL) of silver(I) perchlorate (0.033 mmol). The silver(I) perchlorate solution was added into the reaction mixture dropwise overabout 1 h period. PβCyD-ZrO2/Ag(molar ratio of ZrO2/Ag =0.5/0.5, 0.67/0.33, 0.75/0.25, and 0.8/0.2) nanoparticles thus produced were collected on an ultrafilter, washed with ethanol, anddried under vacuum at 40 ℃. PβCyD-ZrO2/Ag were prepared by
the similar method.
Ultraviolet and visible light (UV-Vis) absorption spectra were
measured with a Shimadzu UV-2500PC recording spectrophotometer using a quartz cell with 10 mm of optical path length. Transmission electron microscopy (TEM) images were observed with a
JEOL JEM 1230 at accelerated voltage of 80 kV. An average diameter and standard deviation were calculated by counting the diameters of 200 particles on the enlarged TEM photographs. PβCyD-ZrO2/Ag nanoparticles were mixed with the liquid crystal
5CB at room temperature resulting in a liquid crystal sol of 5CB
containing 0.075 wt% of ZrO2/Ag. The sols were injected into an
empty cell for a twisted nematic mode with a cell gap of 5 μm, supplied by Sun Trading Co. Ltd. The electro-optic properties, especially applied voltage versus optical transmittance (V-T) curves of twisted nematic liquid crystal displays (TN-LCDs) were measured byapplying the 100 Hz square wave alternating current at 25 ℃ with a
LCD evaluation system (Photal Ohtsuka Electronics, Ltd., model
LC-5200).

3. Results and Discussion
Colloidal dispersions of PβCyD-ZrO2/Ag nanoparticles wereprepared by this method, having a yellow color and being stable formonths at room temperature. No aggregates or sediments were observed in PβCyD-ZrO2/Ag nanoparticles thus prepared. Figure 1
shows UV-Vis absorption spectra of the dispersions of PβCyD-ZrO2/
Ag nanoparticles at various ZrO2/Ag ratios. When a colloidal dispersion of PβCyD-ZrO2 nanoparticles was mixed with silver(I) perchlorate, the absorption at 320 nm of ZrO2 nanoparticles disappeared completely after 1 h. On the other hand, the absorption peakat 423 nm can be attributed to the surface plasmon of Ag nanoparticles.12) This phenomenon suggests that the ZrO2 nanoparticles iscovered by the Ag nanoparticles. The surface plasmon absorption of

Fast Response of Liquid Crystal Devices Doped with Poly(cyclodextrin)-Stabilized ZrO2 /Ag Hybrid Nanoparticles

15

Fig. 1. UV-Vis absorption spectra of colloidal dispersions of PβCyD-ZrO2/
Ag nanoparticles.

Ag can be observed for the colloidal dispersions of ZrO2/Ag
nanoparticles at a ZrO2/Ag molar ratio of 0.8/0.2. When theamount of Ag was larger than 0.2, a strong plasmon absorption was
remarkably observed. In the absence of ZrO2 nanoparticles, the Ag
ions were not reduced in this reaction condition.
Colloidal dispersions of PβCyD-ZrO2/Ag nanoparticles wereprepared by covering ZrO2-core nanoparticles with Ag atoms successively produced by adsorbed on the ZrO2 nanoparticles. Figure 2
depicts transmission electron micrographs and the corresponding
histograms indicating the particle size distributions of nanoparticles. The PβCyD-ZrO2/Ag(0.8/0.2) nanoparticles have an average
diameter of 4.5 nm, while the PβCyD-ZrO2 nanoparticles have 2.2
nm. The size distribution of the PβCyD-ZrO2/Ag nanoparticles exhibits Gaussian distribution. These results suggest that the PβCyD-ZrO2/Ag nanoparticles are not mixtures of ZrO2 and Ag
nanoparticles but consist of single particle having homogeneous
structure. The same tendency was observed in the case of PVP-stabilized core/shell-structured Pd/Ag bimetallic nanoparticles.13) Thisobservation suggests that Ag atoms, produced by reduction of Ag
ions on the surface of the ZrO2 seed, cover the ZrO2 seeds completely to form an Ag shell.
The PβCyD-ZrO2/Ag nanoparticles prepared in the present experiments were easily mixed with liquid crystal molecule 5CB atroom temperature to form liquid crystal sol for TN-LCDs. The TNLCDs fabricated by injecting the liquid crystal sol containing
nanoparticles into empty cells were supplied to measure the electro-optic properties. Electro-optic properties of TN-LCDs fabricated by 5CB with and without PβCyD-ZrO2/Ag nanoparticles were
measured by applying voltage in alternating current at 25 ℃. Figure
3 shows the time evolution of transmittance of TN-LCDs fabricated by 5CB sol in the absence and presence of PβCyD-ZrO2/
Ag(0.8/0.2) nanoparticles and PγCyD-ZrO2/Ag(0.8/0.2) nanoparticles. The response times (τon; the rise time from Von-time to transmittance-10% time, and τoff; the fall time from Voff-time to transmittance-90 % time) of TN-LCDs fabricated by 5CB sol in thepresence of nanoparticles are summarized in Table 1. The fast response time was observed in the presence of PβCyD-ZrO2/Ag
nanoparticles with the τon of 48.8 ms and the τoff of 13.7 ms, while

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Bull. Soc. Photogr. Imag. Japan. Vol. 26 No. 2 (2016)

Fig. 2. Transmission electron micrographs and particle size histograms of ZrO2, Ag and ZrO2/Ag nanoparticles. dav = average
diameter, σ= standard deviation.

Fig. 3. The time evolution of transmittance of TN-LCDs fabricated by 5CB sol in the absence and presence of PβCyD-ZrO2/Ag
nanoparticles and PγCyD-ZrO2/Ag nanoparticles.
Table 1 Response times of TN-LCDs fabricated by 5CB sol in the absenceof nanoparticles, in the presence of PβCyD-ZrO2/Ag and in thepresence of PγCyD-ZrO2/Ag nanoparticles.
Response time / msec

5CB pure

τon

τoff
Total

55.7±0.4
14.5±0.270.2±0.55CB +PβCyD-ZrO2/Ag

5CB +PγCyD-ZrO2/Ag

13.7±1.0

14.3±0.548.8±1.062.5±1.954.2±1.968.5±2.4

The response times depict an average of 5 measured values and standard deviation.

the low response time was exhibited in the absence of them with theτon of 55.7 ms and the τoff of 14.5 ms. The total response times of
TN-LCDs were 62.5 and 68.5 ms for PβCyD-ZrO2/Ag nanoparticles and PγCyD-ZrO2/Ag nanoparticles, respectively. Previously, we
reported that the response time of 5CB in the presence of PβCyD-ZrO2 nanoparticles was faster than that in the presence of
PγCyD-ZrO2 nanoparticles.11) In this ZrO2/Ag nanoparticles, thesame tendency of response time was also observed on TN-LCDs
doped with PβCyD-ZrO2/Ag nanoparticles.
The promotion of response time by PβCyD-ZrO2/Ag is probably
attributable to inclusion complex formation. The 5CB molecule has
a framework of biphenyl. Previously, we have reported the conformation of inclusion complex between βCyD and biphenyl derivativeon alkaline solution by measurements of 1H-NMR chemical shiftsof βCyD and the rotating frame Overhauser enhancement spectroscopy.14) The solubility of ZrO2/Ag nanoparticles in 5CB is poor.
Therefore, bare ZrO2/Ag nanoparticles may be little dispersed in
5CB sol. When ZrO2/Ag nanoparticles is stabilized with PCyD, it
can be disperse in 5CB sol and worked for the TN-LCD. Besides,
the formation constant (2100 dm3 mol-1) of the βCyD–biphenyl
complex was exceedingly lager than that (130 dm3 mol-1) of theγCyD–biphenyl complex.15) Thus, the response time of this LCD in
the presence of PβCyD-ZrO2/Ag nanoparticles is faster than that in
the presence of PγCyD-ZrO2/Ag nanoparticles, suggesting an inclusion complex formation of PβCyD-ZrO2/Ag with 5CB as thehost liquid crystal. In Figure 4, the ZrO2 content of nanoparticles isplotted against the improvement rate of total response time of TNLCDs fabricated by 5CB sol containing PβCyD-ZrO2/Ag nanoparticles from that of pure 5CB. No linear relationship was observed
between the the improvement rate of total response time and ZrO2
content. The improvement rate was larger for ZrO2-core/Ag-shell
nanoparticle of ZrO2/Ag = 0.75/0.25 and 0.8/0.2. The fastest response was acheived by the ZrO2/Ag (0.8/0.2) nanoparticles.
The rise time is given byτon=(γ1d 2)/ε0Δε (Von2 −Vth2)
where γ1, d, ε, and Vth are rotational viscosity, a thickness of host
LCD, dielectric constant, and threshhold voltage, respectively. The

Yukihide Shiraishi, Takahito Kanzaki, Hiroya Sawai, Hitoshi Asano, Yukou Du and Naoki Toshima

Fast Response of Liquid Crystal Devices Doped with Poly(cyclodextrin)-Stabilized ZrO2 /Ag Hybrid Nanoparticles

17ordered liquid crystal media, resulting in easy movement of liquid
crystal molecules. Fast response speed achieved by our present research may give a great impact to LCD industries such as automobile displays, digital signages, and smart phones. Since there are various modes and driving systems in LCDs, the matching between
nanoparticles and liquid crystal media is still in progress to achieve
the improved performance of LCDs.

Acknowledgements

Fig. 4. Relationship between composition and improvement rate of total response time of TN-LCDs fabricated by 5CB sol in the presence of
PβCyD-ZrO2/Ag nanoparticles.

This work was partially supported by Yutaka Kojima Research
Fund of The Society of Photography and Imaging of Japan to Y.S.
and a Grant-in-Aid for Scientific Research (C) (No. 24510158 and
15K04613 to Y.S.) from the Ministry of Education, Culture, Sports,
Science, and Technology (MEXT), Japan.

fall time is given byτoff =(γ1d 2)/(π2Keff )where γ1, d, and Keff are rotational viscosity, a thickness of host
LCD, and Ossen-Frank elastic constants, respectively.16) To consider
this fast response, we measured the rotational viscosity. This measurement was done for an electrically controlled birefringence(ECB) mode cells by a Model 6254 (Toyo). The rotational viscosity
obtained in this manner were 79.9, 68.7, and 75.7 mPa·s for LCDs
in the absence of nanoparticles, in the presence of PβCyD-ZrO2/
Ag(0.8/0.2) and in the presence of PγCyD-ZrO2/Ag(0.8/0.2)
nanoparticles, respectively, as shown in Table 2. This result suggeststhat the presence of PβCyD-ZrO2/Ag nanoparticles in liquid crystal makes it easy for liquid crystal molecules to change the viscosity.
Further studies will be described in detail elsewhere.

4. Summary
PβCyD-stabilized ZrO2/Ag nanoparticles with ZrO2-core/Agshell structure were prepared from PβCyD-ZrO2 nanoparticles. The
response time of TN-LCDs in the presence of PβCyD-ZrO2/
Ag(0.8/0.2) nanoparticles was faster than that in the absence of
nanoparticles. The nanoparticles may work as a disturbant to theTable 2. Rotational viscosity of 5CB doped with PβCyDZrO2/Ag and PγCyD-ZrO2/Ag nanoparticles
5CB Pure

5CB+PβCyD-ZrO2/Ag
5CB+PγCyD-ZrO2/Ag

γ1 /mPa·s
79.9

68.7

75.7

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