Fig. 1: Result of durability test. left:using UV-curable resin, right: usingPVA solution. (a) initial colored state (b)after 50 cycles of heating and cooling.

Fig. 2: Photographs of the lightmodulator. (a) colorless state (60°C) (b)colored state (ambient temperature)

Novel Light Modulating Polymer Gel Materials Imitating Pigment Cell VI--- Design and fabrication of a light modulator

with a light modulation gel layer

H. Tsutsui, M. Mikami, A. Komura, R. AkashiAdvanced Devices & Materials Lab., Corporate Research Group, Fuji Xerox Co., Ltd.

Takematsu 1600, Minamiashigara-shi, Kanagawa, 250-0111, JapanPhone: +81-465-70-1702 Facsimile: +81-465-70-1788 e-mail: Hiroaki.Tsutsui@fujixerox.co.jp

Reversible color changing materials are promising materials for various applications, suchas sensors, displays, and other optical devices. We have already reported novel light modulatingmaterials imitating the manner of the pigment cells of cephalopods utilizing volume-phasetransition properties of polymer gel particles and showed that the dispersion of colored gel particlesin aqueous poly(vinylalcohol) (PVA) solution exhibited excellent light modulating ability1.However, it was still difficult to fabricate devices for long-time use because the aggregation amongthe particles occurred during the repetitive cycles of swelling and shrinking of gel particles. Herewe report a new type of light modulator suitable for various applications. In this light modulator,thermo-responsive colored N-isopropylacrylamide (NIPAM) gel particles were fixed in the softpolymer matrix layer. As a result, the aggregation among the colored gel particles is prevented andthe light modulator can maintain good optical property. Moreover, our light modulator is also highlyflexible and applicable to mass-production.

The light modulator was prepared by the followingmethod; Colored NIPAM gel particles, which were obtainedusing inverse suspension polymerization1, were dispersed inwater-soluble UV-curable resin and the above gel dispersionwas coated on a substrate such as glass plate or plastic filmetc. and cured by UV radiation and sealed. The NIPAM gelparticles performed volume phase transition even in thepolymer matrix of the UV resin. The solvent was hold in thepolymer matrix so that leakage of the solvent from lightmodulation layer did not occur. The measurements oftransmittance change in visible light region revealed that thelight modulator using black NIPAM gel particles altered itstransmittance from 20% to 80 % according to temperaturechange. Furthermore, a durability test revealed that the lightmodulator maintained initial color change abilities evenafter 50 cycles of heating and cooling. On the other hand, alight modulator containing the same colored NIPAM gelparticles dispersed in viscous PVA aqueous solution did notshow such durability against the repetitive cycles due to theaggregation among NIPAM gel particles (Fig. 1). In addition,we also fabricated the flexible film type light modulatorusing plastic film as substrates. Fig. 2 shows flexibility andcolor change property of the light modulator. It is also notedthat our light modulator was highly transparent especially atthe colored state.

Reference1. Akashi, R.; Tsutsui, H.; Komura, A. Adv. Mater. 2002,

14, 1808.

(a)

(b)

(b)(a)

UV resin PVA

Novel Light Modulating Polymer Gel Materials Imitating Pigment Cell VI　 --- Design and fabrication of a light modulator with a light modulation gel layer

Hiroaki Tsutsui, Masato Mikami, Akinori Komura, Ryojiro AkashiAdvanced Devices & Materials Lab. Corporate Research Group, Fuji Xerox.Co., Ltd.

Design and fabrication the light modulation layer which shows excellent light modulation ability, self-supporting property and high durability.

Making flexible devices. High productivity and wide variety of applications utilizing

coating technology.

---- In order to realize these purposes, we designed “gel-in-the-gel” system utilizing water-soluble ultra-violet (UV) curable resin (Fig. 3).

The Structure of The Structure of ““GelGel--inin--thethe--gelgel”” SystemSystem

stimuli

Hydrogel (UV curable resin)

Stimuli-responsive colored gel

MaterialMaterial DesignDesign

Feasibility Study of DeviceFeasibility Study of Device

Akashi, R.; Tsutsui, H.; Komura, A. Adv. Mater., 2002, 14, 1808.

Hirokawa, T.; Tanaka, T. J. Chem. Phys. 1984, 81, 6379

Kokufuta, E; Zhang, Y. Q; Tanaka, T.; Mamada, A. Macromolecules 1993, 26, 1053.

Pigments

Stimuli-responsive Gel

Colored gelparticles are dispersedin aqueous viscous PVA solution.

Stimuli

Muscle

Pigment bag

Pigment

Stimuli-responsive Gel

Stimuli

Heat, pH, Electricity, etc..

UV resin aq.Surfactant

NIPAM gel dispersion

Dispersion

Dispersing

Coating

UV-Curing& Sealing

Introduction

Purpose

Results

Fig. 5. Swelling ratio changes of the colored NIPAM gel particles in aqueous PVA solution as a function of PVA concentration. The diameters (d) are normalized using the fully collapsed state (d0).

Fig. 7. Swelling ratio changes of the colored NIPAM gel particle in aqueous PVA solution and aqueous UV resin (not cured). Polymer concentration: 5 wt%, The diameters (d) are normalized using the fully collapsed state (d0)

Fig. 8. Swelling ratio change of the colored NIPAM gel particle in aqueous UV resin (not cured) solution as a function of concentration of sodium dodecylsulfate (SDS, surfactant). Concentration of UV resin: 5 wt%. The diameters (d) are normalized using the fully collapsed state (d0)

Fig. 9. Swelling ratio change of the colored NIPAM gel particle before and after UV irradiation in the UV resin in the presence of 100 mM of SDS. Concentration of UV resin: 5 wt%. The diameters (d) are normalized using the fully collapsed state (d0)

0%

20%

40%

60%

80%

100%

400 500 600 700 800

Wavelength/nm

Tran

smitt

ance

heating

cooling

Fig. 10. Transmittance spectra and macroscopic color change of the light modulator.Colored state and bleached state were measured at 25℃ and 60℃, respectively.

NIPAM gel particles and solvent were held tightly in the cured UV resin matrix. (PVA-gel)

After 50 heating-cooling cycles

UV resin PVA

UV resin PVA UV resin PVA

UV resin PVA

Colored State Bleached State

Materials and Methods

Conclusions

Optical Property of the Light Modulator Color Variation

Features of the light modulator

0.5

1.0

1.5

2.0

2.5

3.0

20 40 60 80

Temperature/℃

d/d0

150 mM100 mM50 mM0 mM

0.5

1.0

1.5

2.0

2.5

20 40 60 80

Temperature/℃

d/d

0

Before irradiationAfter irradiation

0.5

1.0

1.5

2.0

2.5

20 30 40 50 60

Temperature/℃

d/d

0

PVAUV resin

0.5

1.0

1.5

2.0

2.5

3.0

20 30 40 50 60

Temperature/℃

d/d0

0 wt%1 wt%2.5 wt %5 wt%7.5 wt%

1.5

2.0

2.5

3.0

0 2 4 6 8

PVA concentration / wt%

d/d

0

References

Reversible color changing materials are promising technology for various optical devices. We have reported novel light modulating materials imitating the manner of the pigment cells of cephalopods utilizing volume-phase transition properties of polymer gel particles (Fig. 1). In this system, the transmittance of a device is able to be changed according to the change of the light absorption area of colored gel particles. The dispersion of these colored gel particles showed an excellent reversible light modulating ability (Fig. 2). Now we are trying to apply these materials to various practical optical devices.

Fig. 1. Schematic drawings of the structure and mechanism of the pigment cell of cephalopods such as octopus and squids (upper) and Smart Gel light modulating materials (lower).

Fig. 2. Summary of our previous works. Color change of the colored gel dispersion (upper) and preliminary device(lower) in which colored gel particles were homogeneously dispersed utilizing aqueous viscous poly(vinyl-alcohol) (PVA) solution.

Fig. 3. Design concept of the light modulator. Colored gel particles were dispersed and fixed in the hydrogel matrix utilizing water soluble UV curable resin.

We used N-isopropylacrylamide (NIPAM) gel as a thermo-responsive gel. Colored NIPAM gel spherical particles containing pigments were synthesized by inverse suspension polymerization. Diameters of colored gel particles were about 30 m at swelling state.

Light modulator was fabricated by the procedure described in Fig. 4. We used polyvinyl-alcohol (PVA) based UV-curable resin as a material for self-supporting layer.

Fig. 4. Preparation methods of a light modulator utilizing colored NIPAM gel particles and water-soluble UV curable resin.

Fig. 6. PVA concentration dependence of the diameters of the colored NIPAM gel particles at swelling state. The diameters (d) at swelling state (25℃) are normalized using the fully collapsed state (d0)

Fig. 11. Microphotographs of colored NIPAM gel particles dispersed in UV resin layer at swelling (a) and shrinking (b) state. Swelling and Shrinking state were measured at 25℃and 60℃, respectively. (c) Magnified photograph. Scale bars in photograph: 50 m.

(a)

(b)

(c)

Fig. 12. Result of durability tests. Before heating-cooling cycles (upper). After heating-cooling cycles (lower) Colored state and bleached state were measured at 25℃ and 60℃, respectively.

Fig. 13. Flexible light modulator. PET film was used as substrates. Colored state and bleached state were measured at 25℃(a) and 60℃ (b), respectively.

Fig. 14. Color variations of the light modulators. Purple (lower left) was made by mixing magenta (upper right) particles and blue (lower right) particles. Colored state and bleached state were measured at 25℃(a) and 60℃ (b), respectively.

We designed and fabricated a light modulator utilizing “gel-in-the-gel” layer in which colored NIPAM gel particles are held in the water-soluble UV resin matrix. The results are as follows.

Volume-phase transition of colored NIPAM gel particles was observed in cured UV resin (PVA-gel) and the light modulator utilizing this system showed excellent light modulating ability.

Gel particles and the solvent were held in the resin matrices so tightly that we succeeded in preventing the leak of the solvent.

The light modulator showed excellent stability under repetitive cycle, because of the prevention of the aggregation among gel particles.

A flexible light modulator can be fabricated with flexible substrates such as PET film.

Color change temperature can be controlled using ionic surfactant (SDS). The light modulators with a variety of color were obtained by introducing various

color pigment in the gel or mixing different colored gel particles.

(a) (b)

(a) (b)

Pigment Cell of CephalopodsPigment Cell of Cephalopods

Smart GelSmart Gel

Our group is now trying to develop practical devices taking advantage of the strong points of our material. To be specific, Energy-saving Glass (utilizing UCST gel) Optical Devices (e.g. Optical switch) Display Devices Optical Sensors etc.

Future and Outlook

Phase-transition properties in PVA aq. and UV resin

Light Modulator