Crystalline Colloidal Array Crystalline Colloidal Array Optical DevicesOptical Devices

Sanford A. AsherSanford A. AsherDept. of ChemistryDept. of Chemistry

University of PittsburghUniversity of PittsburghPittsburgh, PA 15260Pittsburgh, PA 15260

412412--624624--85708570asher@pitt.eduasher@pitt.edu

Sanford A. Asher, Department of Chemistry

CRYSTALLINE COLLOIDAL SELF-ASSEMBLY:

MOTIF

FOR

CREATING SUBMICRON

PERIODIC SMART MATERIALS

OutlineOutlineCCA and PCCA Photonic Crystal CCA and PCCA Photonic Crystal FabricationFabricationNanosecond Photonic Crystal SwitchesNanosecond Photonic Crystal SwitchesHydrogelHydrogel Volume Phase Transition Volume Phase Transition Refractive Index SwitchingRefractive Index Switching–– Thermally activatedThermally activated–– Chemically activatedChemically activated–– PhotochemicallyPhotochemically activatedactivated

Sanford A. Asher, Department of Chemistry

Holtz, Asher et al J. Am. Chem. Soc. 1994, 116, 4497

Crystalline Colloidal Arrays Self-Assemblyfabricated from monodisperse, highly charged colloidal particles

~ 1013 spheres/cm3

spacing dependent only upon particle number density and crystalline structure

-

Dialysis /Ion Exchange Resin

Self-assembly

Crystalline Colloidal Array

FCC--

----

- --

+

-

--

---

- --

+

--

---- -- -

--

--- ---

--

--- -

-

--

---

- --

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+ +

--

---- --

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--

---- --

+ +

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++

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+ +

++

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- ---

--

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---- --+

+

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--- --+

+

--

---- --+

+

+

+--

--- --+

---

-- -- ++

+

+

+

+

+

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+

+

++

+

+-

-

--

-+

+

+

+

+

+

-

---

----

-+

+-

- -

Preparing ~ 100 nm Polystyrene Colloids

160 ml Water 60 ml Styrene (monomer) 2.00 g MA-80-1 (surfactant) 2.90 g COPS -1 (ionic co-monomer)2.00 g Divinyl Benzene (crosslinker)0.20 g Sodium Bicarbonate (buffer)0.70 g Ammonium Persulfate (initiator)

Polymerize at 70oC for 3 hrs.

Polystyrene Colloid Synthesis:EMULSION POLYMERIZATION

TEM of polystyrene spheres

Reese, Asher et al J. Colloid Interface Sci. 2000, 232, 76

Temperature ControllerN2

N2

H2O

-

Long polymer chain

Surfactant

Water

-

--

++

+

R•

R•

What Drives CCA Self-Assembly?

Medium Dielectric Constant

re

aeeZrU

ra κκ

κε

−

⎥⎦

⎤⎢⎣

⎡+

=222

1)(

Interaction Potential Energy

Sphere Radius

Ionic Impurities

( )ipB

nZnTk

e+=

επκ

22 4

Particle concentration

2ar

U

r

H+ SO3-

-O3SH+

+H H+

H+

-O3S-O3S

-O3S SO3-SO3

-

SO3-

+H

+H

+H

Shear boundary

Negatively charged particle

Debye layer thickness

nmwaterpurein 700~)(1κ

Sanford A. Asher, Department of Chemistry

Bragg Diffraction

Diff

ract

ed In

tens

ity, I

D

500 600 700 800Wavelength / nm

d ~ 200 nm

+

- - - - --------- -- - -

-

-

---

--

- - - - ------------ -

-

-

---

--+ + +

λ0

- - - - -------------

-

-

---

--- - - - ---

--------- -

-

-

---

--

- - - - ------------ -

-

-

---

--- - - - ---

--------- -

-

-

---

--

- - - - -------------

-

-

---

--

- - - - ------------ -

-

-

---

--

- - - - -------------

-

-

---

--

- - - - -------------

-

-

---

--

- - - - ------------ -

-

-

---

--- - - - ---

--------- -

-

-

---

--

- - - - -------------

-

-

---

--

- - - - ------------ -

-

-

---

--

+

+

++

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

dθB

mλo = 2ndsin θ

(111) FCC CCA

λ0 = wavelength of diffracted light n = refractive index of systemd = interplanar spacing in crystalθB = Bragg glancing angle

All Light Diffracted-Finite Widths-Top Hat Profiles

Diffraction Phenomena of Photonic Crystals

* Kinematic Diffractionx-rays: Atomic & Molecular Latticewimpy scatteringlittle attenuationeach layer contributes similarly

* Dynamical Diffractionstrong scatteringmust consider coupledincident and diffracted wave

* Theoretical Foundation Based on Work in1930-1940

W.H. Zachariasen, The Theory of X-ray Diffractionin Crystals, Wiley, 1945.

3-D Photonic Bandgap Crystals-for much larger modulations of refractive index

Dynamical Bragg Diffraction From Crystalline Colloidal Arrays, P. A. Rundquist, P. Photinos, S. Jagannathan, and S. A. Asher, J. Chem. Phys. 91, 4932-4941 (1989).

Ultra Efficient Diffraction

0 200 400 600 800 1000

0

2

4

6

8

10

-Log

T91 nm PS CCA

100 μm = 400 layers

Number of fcc (111) layers

A B

C

FCC: ABCABCABC…

FCC Twin: ABCABCBACBA…

Twin Planes

HCP: ABABABAB…

Stacking of closest-packed layers:

FCC Twin: ABCABCBACBACBABCABC…Lamellar

A B

C

FCC: ABCABCABC…

FCC Twin: ABCABCBACBA…

Twin Planes

HCP: ABABABAB…

Stacking of closest-packed layers:

FCC Twin: ABCABCBACBACBABCABC…Lamellar

FCC Crystal

0

.5

1

1.5

2

2.5

3

400 600 800 1000 1200 1400

L U

X

W

K

L

X

Wavelength (nm)

-log

10T

U

σ polarization

CCA in the middle: ABCABC layers. Reciprical lattice and unit cell.

Sanford A. Asher, Department of Chemistry

(-200)(0-20)

(-2-20)

Incident light

0 5 10 15 200

0.1

0.2

0.3

0.4

0.5

% stacking faults

Diff

ract

ed in

tens

ity ra

tio(200)/(111)(220)/(111)(311)/(111)

Dependence of Diffraction Efficiency on Number of Stacking Faults Along 111

Conclusions

• Diffraction from FCC 111 planes independent of stacking faults

• Diffraction from higher Miller index planes severely attenuated by stacking faults

• Stacking faults increase with particle spacing

• Stacking faults will be the major difficulty for fabricating 3-D photonic bandgapmaterials

Crystalline Colloidal Array Optical Crystalline Colloidal Array Optical DevicesDevices

••Passive Spectral Passive Spectral BandpassBandpass Reject FilterReject Filter

-log

T

λ-7

0 EXP: Raman Spectroscopy

rejecting Rayleighline, Δλ = 5 nm

First Photonic Crystal PatentSanford A. Asher, Department of Chemistry

Photonic CrystalsHave Revolutionary

Applications in Areas Such as Optics,

Optical Computing and Communications.

Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices

•Refractive index thermal nonlinearities

•Hydrogel volume phase transitions

•Photochemically accuated lattice alterations

No Transmission

100% Transmission

Low Intensity

High Intensity

?

?

Optical Limiter and Switch

Sanford A. Asher, Department of Chemistry

Concept for Creating Nonlinear Optical Switch

Low intensity illumination :

High intensity illumination causes the sphere refractive indexto mismatch that of the medium - Bragg diffraction occurs.

no transmission

CCA

100% transmission

CCA

index matched (np = nm)

≠index mismatched (np nm)

Transmission Through CCA as a Function of the Refractive Index Between the

Spheres and the Medium

Nanosecond PhotothermalDynamics in Colloidal Suspension

R. Kesavamoorthy, M. S. Super, and S. A. Asher,

J. Appl. Phys. 71, 1116-1123 (1992).

Nanosecond Photothermal Dynamics in Colloidal SuspensionR. Kesavamoorthy, M. S. Super, and S. A. Asher, J. Appl. Phys. 71, 1116-1123 (1992).

Refractive Index Dependence on Temperature

Photothermal Effect: Δn = (dn/dT) · ΔT

Example: PMMA, dn/dT = -1.1 X 10-4 / 0° C×

Requirements:(1) To index match the particles to the aqueous medium (nH2O = 1.33), we need to use a low refractive index polymer to synthesize the particles.(2) We need to chemically bond a dye to the particles in order to prepare transparent, absorbing CCA.

OCH2CF2CF2CF3

OC

CH2 CHn( )

Wavele ngth / nm

Ext

inct

ion,

-log

(It/I

0)

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

500 550 600 650 700 750 800

medium refractive index, nm

Ext

inct

ion

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.34 1.36 1.38 1.40 1.42 1.44 1.46

np > nm = 1.333

np > nm = 1.437

Transmission Spec tra of PFB MA Pol ymerize d CCA at Di fferent Me dium Re frac ti ve Inde x

A ~ ( n p /n m )2 - 1

Dyed PFBMA CCA Hydrogel

0

0.2

0.4

0.6

0.8

1.0

400 450 500 550 600 650 700 750 800

Wavelength (nm)

Ext

inct

ion

dye absorption band

diffraction band

Covalently attached absorbing dye to the CCA in the hydrogel.

PCCA FabricationPCCA Fabrication

--

---- --

--

---- --

--

---- --

--

---- --

--

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---- ---

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---- -- -

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---

- --

+

+

++

+

++

+

+++

+

++

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+

+

+

+

++

+

+

+

+

+

++

+

+

+

+

+

+

+

+ + ++

++

+ +

+

++

+

+ + --

---

- --

--

---

- --

--

---- --

--

---- --

--

---- --

--

---- --

--

---

- --

--

---

- ----

---- --

--

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---- ---

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- --

--

---

- ----

---

- ----

---- --

--

---

- --

--

---- --

--

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--

---- --

--

---- --

--

---- --

--

---- --

--

---- --

--

---- -- -

----

- --

--

---

- --

--

---- --

--

---- --

--

---- --

+

+

++

+

++

+

+++

+

++

++

++

++

+

+

+

+

++

+

+

+

+

+

++

+

+

+

+

+

+

+

+ + ++

++

+ +

+

++

+

+ +AcrylamideBisacrylamide

Photopolymerize

Self Assembly Motif for Creating Submicron Periodic Materials. Polymerized Crystalline Colloidal Arrays,

S. A. Asher, J. Holtz, L. Liu, and Z. Wu, J. Am. Chem. Soc. 116, 4997-4998 (1994).

Experimental Set-up For Measuring Optical

Switching Nonlinearity

Pump beam

Probe beam

532 nm

594 nm D1

beam splitter

lens

cylinder with DMSO/water

CCA hydrogel sample

(reference signal)(diffraction signal)

shutter

D2

Medium indexn0E

xtin

ctio

n

Optical Switching of Dyed PCCA

nm (1.390) > np (1.386) , dyed PCCA

nm (1.382) < np , dyed PCCA

nm (1.388) > np , undyed PCCA

Incident Pump Beam Energy (mJ)

Ron

/ R

off

0.4

0.60.81.0

1.2

1.41.6

1.8

2.0

2.22.4

0 0.5 1.0 1.5 2.0 2.5 3.0

Tg = 62 0C

Nsec Switchable Polymerized Crystalline Colloidal Array Bragg Diffracting Materials

G. Pan, R. Kesavamoorthy, and S. A. Asher

J. Am. Chem. Soc. 120, 6525-6530 (1998).

1.0

1.5

2.0

2.5

3.0

-4 -2 0 2 4 6 8

Probe delay time / ns

Ron

/Rof

fat

Tg

Dependence of Nonlinear Effect on Probe Delay Time

Nsec Switchable Polymerized Crystalline Colloidal Array Bragg Diffracting Materials

G. Pan, R. Kesavamoorthy, and S. A. Asher

J. Am. Chem. Soc. 120, 6525-6530 (1998).

Conclusions

• Observed nsec photothermal switching• Problem low efficiency (<10%) !• Stay Tuned: Inefficiency results from

temperature dependence of diffraction λ• Switching should be 99 + %

Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices

Refractive index thermal nonlinearities

•Hydrogel volume phase transitions

•Photochemically accuated lattice alterations

Poly(N-isopropylacrylamide) : T Dependent ΔGMIX

Chemical Structure of NIPAMPoly(N-isopropylacrylamide) (PNIPAM) undergoes a reversible phase transition when heated above 32.1 oC. This coil-globule transition is analogous to a liquid-vapor phase transition. The recipe and synthesis conditions determine the extent of volume changes and whether they are continuous or discontinuous.

ON

ON

Sanford A. Asher, Department of Chemistry

Thermally Switchable Periodicities from Novel Mesocopically Ordered Materials J. M. Weissman, H. B. Sunkara, A. S. Tse , and S. A. Asher

Science 274, 959-960 (1996).

Extin

ctio

n (-l

og I/

I o)

Optical switching from PNIPAM CCA

600

Wavelength (nm)

40 oC

10 oC

0

0.5

1

1.5

2

400 450 500 550

10 oC

40 oC

Sanford A. Asher, Department of Chemistry

Sanford A. Asher, Department of Chemistry

Unfortunately system does not switch quickly-

CCA disorders!

HydrogelMatrix

PNIPAM Colloid

MonomerCrosslinker

InitiatorUV

Polymerization

NIPAM CCA Lightly Polymerized into PCCA

“Nanogel Nanosecond Photonic Crystal Optical Switching,”

C. Reese, A. Mikhonin, M. Kamenjicki, A. Tikhonov and S.A. Asher

J. Am. Chem. Soc., 126, 1493-1496 (2004).

0

0.5

1

1.5

2

2.5

3

200 300 400 500 600 700 800 900 1000

Wavelength / nm

Abs

orba

nce

10 C15 C20 C25 C28 C30 C32 C34 C37 C40 C45 C

0.2

0.4

0.6

0.8

1

1.2

1.4

5 10 15 20 25 30 35 40 45 50

Temperature / C

Abs

orba

nce

at 7

16 n

m

40oC

20oC

PNIPAM Colloid

Wavelength / nm

0

.5

1

400 500 600 700

.5

1

400 500 600 700

.5

1

400 500 600 700

.5

1

1.5

400 500 600 700

−lo

g T

Wavelength / nm

4 ms

54 μs

9 μs

1.5 1

100 ns

0.48 ms0.3 ms

24 μs

1.5 μs1 μs

800 ns 600 ns 300 ns

0

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680

−lo

g Δ

T

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680 W avelen gth / nm

T

Wavelength / nm

0

.5

1

400 500 600 700

.5

1

400 500 600 700

.5

1

400 500 600 700

.5

1

1.5

400 500 600 700

−lo

g T

Wavelength / nm

4 ms

54 μs

9 μs

1.5 1

100 ns

0.48 ms0.3 ms

24 μs

1.5 μs1 μs

800 ns 600 ns 300 ns

0

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680

−lo

g Δ

T

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680 W avelen gth / nm

T

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680

−lo

g Δ

T

.1

.2

.3

.4

56 0 600 64 0 680

.1

.2

.3

.4

56 0 600 64 0 680 W avelen gth / nm

T

Time Dependence of Diffraction Changes after 3 nsec T-jump

Kinetics

−Lo

g T

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

Delay time / μs

−Lo

g T

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

Delay time / μs

−Lo

g T

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

Delay time / μs

−Lo

g T

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

605 nm

0 40 80 1200.01

0.1

1

τ1 ≈ 870 ns (26%)

τ2 ≈ 19 μs (24%)

τ3 ≈ 130 μs (50%)

Delay time / μs

0 40 80 1200.01

0.1

1

−Lo

g T

Delay time / μs

375 nm

τ1 ≈ 1.2 μs (28%)

τ2 ≈ 21 μs (11%)

τ3 ≈ 147 μs (61%)

0 40 80 1200.01

0.1

1

0 40 80 1200.01

0.1

1

−Lo

g T

Delay time / μs

375 nm

τ1 ≈ 1.2 μs (28%)

τ2 ≈ 21 μs (11%)

τ3 ≈ 147 μs (61%)

0 40 80 1200.01

0.1

1

−Lo

g T

Delay time / μs

375 nm

τ1 ≈ 1.2 μs (28%)

τ2 ≈ 21 μs (11%)

τ3 ≈ 147 μs (61%)

0 40 80 1200.01

0.1

1

0 40 80 1200.01

0.1

1

−Lo

g T

Delay time / μs

375 nm

τ1 ≈ 1.2 μs (28%)

τ2 ≈ 21 μs (11%)

τ3 ≈ 147 μs (61%)

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

Wavelength / nm

ΔOD

0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec

0 1 2

0.0 5

0.0 6

0.0 7

0.0 8

600 nm

τ ≈ 120 ns

Delay tim e / μs0 1 2

0.0 5

0.0 6

0.0 7

0.0 8

600 nm

τ ≈ 120 ns

Delay tim e / μs

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

Wavelength / nm

ΔOD

0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

Wavelength / nm

ΔOD

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

.05

.1

.15

400 450 500 550 600 650

Wavelength / nm

ΔOD

0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec

0 μsec0.1 μsec0.2 μsec0.3 μsec0.4 μsec2.5 μsec20 μsec200 μsec1000 μsec1500 μsec

0 1 2

0.0 5

0.0 6

0.0 7

0.0 8

600 nm

τ ≈ 120 ns

Delay tim e / μs0 1 2

0.0 5

0.0 6

0.0 7

0.0 8

600 nm

τ ≈ 120 ns

Delay tim e / μs

NSec Individual Sphere Volume Phase Transitions

Fast Kinetic Transmission Changes in

PNIPAM Photonic Crystals.

• Heating pulse: 3 ns duration, 1.9 μm, ~1.3

mJ/pulse

• T-jump ~ 23°C → 30°C ± 2°C, IR spot

diameter ~ 200 – 300 μm

• Transient absorption probed by temporally

delayed 120 ns “white-light” pulse

Crystalline Colloidal Array Crystalline Colloidal Array Tunable Optical DevicesTunable Optical Devices

•Refractive index thermal nonlinearities

•Hydrogel volume phase transitions

•Photochemically accuated lattice alterations

PHOTORESPONSIVEPOLYMERIZED CRYSTALLINE COLLOIDAL ARRAYS

AS A PHOTOSWITCHABLE DEVICE

Marta Kamenjicki, Igor K. Lednev, Sanford A. Asher

Department of ChemistryUniversity of Pittsburgh

Pittsburgh, PA 15260

N

N

N

N

Photochemically Controlled Photonic Crystals, M. Kamenjicki, I. Lednev, A. Mikhonin, R. Kesavamoorthy and S.A. Asher, Advanced Functional Materials, 13, 774-780 (2003).

λ1

O

O CHO

CH2CH2

λ1

UV

Vis, Δ

Trans -

N

HN

N O

OH

HO

λ2

Cis -

N N

HO

OHON

H

H2N-R

R=N O

OH

HO

N

PCCA PCPCCA PCPCCA

UV

AZOBENZENE PHOTOISOMERIZATION

VIS, VIS,

• reversible photochromism in fluids and solids

• isomerization results in changes of1) absorption spectrum2) dipole moment3) geometrical conformation

Trans-azobenzene Cis-azobenzene

60°

N

N

180°

9.0 Å

N N

5.3 Å

Azobenzene (water solution) Dynamics UnderUV and Vis Light

200 300 400 500 600 7000.0

0.5

1.0

Abs

orba

nce

Wavelength /nm

Dark

1 min 365 nm (12 mW)

20 sec. 488 nm (50 mW)

NH2N

N O

OH

OH

N

N

UV

Vis,

N N

200 300 400 500 600 7000.0

0.5

1.0

Abs

orba

nce

Wavelength /nm

Dark

1 min 365 nm (12 mW)

20 sec. 488 nm (50 mW)

NH2NH2N

N O

OHOH

OHOH

N

N

N

N

UV

Vis,

UV

Vis,

N NN N

1 cm quartz cell

Azobenzene Functionalized PCCA Dynamics Under UV and Vis Light

0

0.4

0.8

-log

T

350 450 550 650 750

Wavelength /nm

UV

Vis

Vis

UV

0.6

0.8

A (

340

nm)

Time

Peak

pos

ition

/a.u

.

Time

UVVisUV

a)

b)

0

.2

.4

.6

.8

360 400 440 480 520 t = 0.3 μs

0

.2

.4

.6

.8

360 400 440 480 520

t = 102.3 μs0

.2

.4

.6

.8

360 400 440 480 520

t = 302.3 μs

0

.2

.4

.6

.8

360 400 440 480 520

t = 2002.3 μs0

.2

.4

.6

.8

360 400 440 480 520 t = 6155.8 μs

0

.2

.4

.6

.8

360 400 440 480 520

t = 5.3 μs

Wavelength /nm

Wavelength /nm

Wavelength /nm

Wavelength /nm

Wavelength /nm

Wavelength /nm

0

.2

.4

.6

.8

360 380 400 420 440 460 480 500 520 540 Wavelength /nm

Fig. 11

0 s15 s36 s66 s120 s-lo

g T

Speed

Limit?

Optical Switching

• Use of Laser Heating to Drive HydrogelVolume Phase Transition

• Use of Photochemistry to Drive HydrogelVolume Phase Transition

• Use of Thermal Refractive Index Mismatch to Control Diffraction-Inefficiency due to dynamic diffraction wavelenght shift-stay tuned

FUTURE WORK

• Optimize these sensors to combine hydrogel volume phase transition with thermal heating by nsec pulses

• Available Δn > 0.15 !• Decrease characteristic size of switching

materials.

AcknowledgementsAcknowledgements

Asher Research Group Members

$: NIH, NCI, NASA and NSF