Photoaddressable Block Copolymers as Material …...Photoaddressable Block Copolymers as Material for Volume Holographic Data Storage Carsten Frenz, Michael Häckel, Lothar Kador,

Universität BayreuthMakromolekulare Chemie I

Photoaddressable Block Copolymers as Material

for Volume Holographic Data Storage

Carsten Frenz, Michael Häckel, Lothar Kador,

Hans-Werner Schmidt

Makromolecular Chemistry and Experimental Physics

Bayreuther Institut für Makromolekülforschung (BIMF)Universität Bayreuth, Germany

International Materials Forum, 1. August 2005

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Photoaddressable block copolymers

Motivation

Fundamental aspectscontrol of multi-level order on different length scalesmanipulation on nanometer scalephotochemistry in confined geometries

Application possibilitiesholographic data storage

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Development of storage capacity

3 disks

3-dimensional“Volume holographic storage”

2-dimensional+ stacking

Bayer Research 10, September 1998modified

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Volume holographic digital data storage

J. Ashley et.al., IBM J. Research Development 44(3) 2000, modified

Recording principle Irreversible materials:• photopolymer (Polaroid)• PQ doped PMMA

Reversible materials:• LiNbO3• LiNbO3:Fe• photoaddressable polymers

PQ: phenantrenequinone

1024 x 1024 Pixel

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Volume holographic digital data storage

Reading principle

J. Ashley et.al., IBM J. Research Development 44(3) 2000, modified

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Optical data storage

Material requirements for volume holographic storage

• photoeffect (local modulation of refractive index)

• sufficient high ∆n

• excellent optical quality throughout the sample

• sample thickness of 1–2 mm (hologram multiplexing)

• optical density 0.5 - 0.7 (utilizing of total volume)

• low response time (milliseconds)

• long-term stability of the stored information

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Photoaddressable polymersLight-induced isomerization N

N

N Nhν

hν ' and kT

Azo-dye containing side-group polymers

source: BAYER AG

polarization plane

chromophores orient perpendicular to the polarization plane

M. Eich, J.H. Wendorff, H. Ringsdorf, H.-W. Schmidt, Makromol.Chem. 186, 2639 (1985). BAYER-research, 36 (1999). R.H. Berg, S. Hvilsted, et al., Nature 383, 505 (1996). X. Meng, A. Natansohn, et al., Polymer 38 (11), 2677 (1997). And others.

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Polymer systems for holographic storage• Doped polymers

migration, macrophase separation, stability

• Homopolymers

too high optical density, formation of surface gratings

• Polymer blends

macrophase separation results in bulk scattering

• Statistical copolymers

loss of cooperative effect

Block copolymers

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Photoaddressable block copolymersBlock copolymers

Self organization into ordered nanophase separated morphologies

Spheres Cylinders Gyroid Lamellae

10-50 nmvolume fraction

Advantages as holographic storage material• localized concentration and confinement of addressable units• cooperative effect• no bulk scattering• control of optical density• no formation of surface gratings• low shrinkage

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Block copolymers with PS matrix

n

O O

O

Hm b

hydroborated 1,2-polybutadiene

ester linkage from polymeranalogous reaction

azo chromophore side group

polystyrene

Block copolymer composition: polystyrene as matrix

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Synthesis of functionalized block copolymers

Ini IniR R R

RIni +

-

Sequential anionic polymerization

Conversion to hydroxy function

IniR R R Ini

R R R

Polymeranalogous reaction with functional side groups

IniR R R

IniR R R

Synthetic advantages: • easy purification of monomers• activation of low molecular functional side groups• polymeranalog. reaction allows variation of side groups

G. Mao et al. Macromolecules, 1997, 30, 2556-2567. J. Adams et al. Makromol. Chem., Rapid Commun. 1989, 10(10), 553-557

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Sequential anionic polymerization

Lin n

Hm

Cyclohexane6°CDIPIP / s-BuLi 10 / 1

1. 10% THF

2. MeOH

10°C

DIPIP: DipiperidinoethaneHalasa et al.

n H

m

n H

m

OH

1. 9-BBN2. NaOH3. H2O2

9-BBN: 9-Borabicyclo[3.3.1]nonan

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Block copolymers with methoxyazo chromophore

n H

m

OH

n

O O

O

Hm

N N

O CH3

ChromophorCl C

O

excessdry THF, pyridine

Block Weight fraction Mn Mw/Mn Glass transitions copolymer PS / methoxyazo

(wt.-%) (g/mol) Tg1(°C) Tg2(°C)

OMe-1 75 / 25 68100 1.07 104 66 OMe-2 82 / 18 59000 1.04 101 n.d. OMe-3 89 / 11 56000 1.03 97 n.d. OMe-4 98 / 2 52000 1.02 101 n.d.

cylindercylinderspheremiscible

(C. Frenz)

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Holographic writing curve

0 100 200 3000

1

2

3

4writing laser off

time [seconds]

writing time: 250 s 50 s 10 s 2 s

n 1n1

max[1

0-3]

Block copolymer azo content: 25 wt. %

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Azo-dye containing side-chain polymers

homopolymer

statistical copolymer

block copolymer miscible

block copolymer with spherical and cylindrical morphology

O

O

N N

OMe

solid-state with no liquid crystalline order

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Holographic experiments

Influence of block copolymer morphology

0 10 20 30 90 1000

2

4

6

8

10

wt.% azo-unit

0.0

0.1

0.2

0.3

0.4

0.5

homo

stat.blockmisc.

blockS

blockC

blockC

n 1m

ax[1

0-3]

Block copolymer series

n

O O

O

Hm

N N

OMe

b

n1 m

ax/c [10-3]

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Long-term stability

0 5 10 15 200,00,20,40,60,81,01,21,4

statistical methoxy

block methoxycylinder

diffr

actio

n ef

ficie

ncy

[a.u

.]

time [days]

η: diffraction efficiency

I1(t) – 1st order diffracted beam

I0(t0) – transmitted beam

)()(

00

1

tItI

=

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Materials

Partial replacement of azo-units with non-absorbing mesogens

Concepts to decrease the optical density and maintainingsufficiently high n1 values

Introduction of liquid crystalline order and increaselong term stability

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Photoaddressable materials

Block copolymers with azo side-groups and mesogenic units in the photoaddressable segment

O O

O

N N

OMe

O O

O

O O

OMe

x

y

n

m

bco

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Holographic experiments

O O

O

N N

OMe

O O

O

O O

OMe

x

y

n

m

bco

Block copolymer

0 10 20 30 90 1000

2

4

6

8

10

wt.% azo-unit

0.0

0.1

0.2

0.3

0.4

0.5

blockazoC

blockmesogen/azo

Cn 1m

ax[1

0-3]

∆n1 m

ax/c [10-3]

Azo content: 13 wt.% Repeating units: PS = 445; Azo = 24; Mesogen = 24Molecular weight: Mn 66000 g/molGlass transition: Tg1 = 39 °C; Tg2 = 99 °C

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Long-term stability

n

O

Hm

O

O O

O

N N

OMe

co

O O

O

N N

OMe

O O

O

O O

OMe

x

y

n

m

bco

n

O O

O

Hm

N N

OMe

b

diffr

actio

n ef

ficie

ncy

[a.u

.]

0 5 10 15 200,0

0,2

0,4

0,6

0,8

1,0

1,2

time [days]

block azo/mesogenblock azostat.

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Long-term stability

0.01 0.1 1 10 100 10000.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

35 mol%

52 mol%

0 mol%

14 mol%n 1/n1(t

= 0)

time [days]

Stability of the written gratings for different mesogen concentrations

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Volume holographic data storage

Sample thickness vs. optical density

ε488 = 751 l ⋅ cm-1⋅mol-1

0,0 0,5 1,0 1,5 2,00

1

2

0.25 wt.%

0.5 wt.%

10-30 wt.%ab

sorp

tion

[a.u

.]

film thickness [mm]

investigatedblock copolymers

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Materials

Blends of block copolymer with homopolymer

Concepts to decrease the optical densityto obtain thick samplesfor volume holographic data storage

Thermoplastic material injection molding

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Injection molded samples

Blend of homopolymerwith polystyrene

Blend of block copolymerwith polystyrene

thickness: 1.1 mm

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Blend of block copolymer (10 wt%) with polystyrene homopolymer (90 wt%)

Optical light microscopy between crossed polarizers

thickness: 1.1 mm

(b) between parallel polarizers

(a) sample with inscribed gratings betweencrossed polarizers

25 mm

(c) first diffraction order

transmission: 69.1haze: 3.7clarity: 98.9

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Block copolymer: CF110Azo dye: methoxyazobenzene; content: 17.5 wt.% Repeating units: PS = 467; Azo = 28Molecular weight: Mn 59000 g/mol

Blend composition:10 wt% block copolymer90 wt% polystyrene homopolymerthickness: 1.1 mm

2019

1817

1615

14

20 holograms

writing: λ 514 nm

writing time:0.5 s @ 2 W/cm2

writing energy:1 J/cm2

reading:λ 685 nm



Block copolymer: DK25Azo dye: methoxyazobenzene; content: ≈ 5 wt.% Molecular weight: Mn 60000 g/mol


80 holograms

writing: λ 514 nm

writing time: 1 s @ 1 W/cm2

writing energy: 1 J/cm2

reading: λ 685 nm

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200 holograms

writing: λ 514 nm

writing time: 0.3 s @ 1 W/cm2

writing energy: 300 mJ/cm2

reading: λ 685 nm


Block copolymer: DK25Azo dye: methoxyazobenzene; content: ≈ 5 wt.% Molecular weight: Mn 60000 g/mol

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Angular multiplexing of images

Blend of block copolymer (10 wt%) with polystyrene homopolymer (90 wt%)

Eight reconstructed holographic images, written at the same location

angular distances 1wavelength 514 nms:s-polarization2 J/cm2 per hologram

thickness: 1.1 mm

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Acknowledgement

Coworkers and collaboration partners

Dietrich Haarer and Daniela Kropp

Funding:SFB 481 Project B2 (German Science Foundation)BAYER AGFonds of the Chemical Industry

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Documents

Photoaddressable Block Copolymers as Material …...Photoaddressable Block Copolymers as Material for Volume Holographic Data Storage Carsten Frenz, Michael Häckel, Lothar Kador,