Large aggregate species in conjugated polymer solutions characterized by dynamic light scattering and in situ

rheological/flow turbidity measurementsChih J. Lin1, Chan Y. Kuo1, Chi C. Hua1,* Show A. Chen2

1Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621,Taiwan, R.O.C.2Department of Chemical Engineering, National Tsing Hua University, Hsin-Chu 300, Taiwan, R.O.C.

Date: 2008/07/01

Complex Fluids & Molecular Rheology Laboratory, Department of Chemical Engineering,

National Chung Cheng University, Chia-Yi 621, Taiwan, R.O.C.

Speaker: Chi C. Hua （華繼中）

Imagining PLED display

Spin-coating

Casting

Ink-jet printing

Films

Electro-luminescent conjugated polymer film

Aggregation Properties in MEH-PPV Aggregation Properties in MEH-PPV SolutionsSolutions

1 / T

0.0028 0.0030 0.0032 0.0034 0.0036 0.0038

0 M

/cR

T(s

)

1e-6

1e-5

1e-4

chloroform, heatingchloroform, annealingtoluene, heatingtoluene, annealing

278288298308T (K)

318338348 328

Thermal irreversibility in the solutionViscosity—Existence of unstableaggregation properties

Hua et al, J Rheol 49, 641 (2005)

Poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene]

(MEH-PPV)

Mw: 70,000-10,000 g/molPDI: 2.5

5mg/ml

Parameter-Free Coarse-Grained SimulationsParameter-Free Coarse-Grained Simulations

Which yields the exact (generally poor) solvent qualities for MEH-PPV solutions:Toluene: 0.32 Chloroform: 0.38

cf. Theta condition: 0.50

log N

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

log

R

1.2

1.4

1.6

1.8

2.0

2.2

2.4

MEH-PPV / Toluene MEH-PPV / Chloroform

log log log

0.32 0.02, 1.07 0.05

0.38 0.01, 1.07 0.03

R a N b

a b

a b

Scaling behavior of the mean end-to-end distance:

No. of MEH-PPV (m )ono : 100 ~ 500mers N

g,MT

p,MT

11 2G, MT

34.4 0.7 (A)

65.1 11.8 (A)

7.51 10 (m /s)

R

L

D

g,MC

p,MC

11 2G, MC

43.7 0.5 (A)

73.3 12.5 (A)

9.62 10 (m /s)

R

L

D

50 MEH-PPV monomersper Kuhn length

2 1/ 2end-to-end Kuhn/ 0.5 ~ 0.8R l

highly collapsed chain conformation

Dynamic Light Scattering (DLS)/Photoluminescence (PL): Effects of solvent quality and concentration

(s)

100 101 102 103 104 105 106

g(1

) ()

0.0

0.2

0.4

0.6

0.8

1.0

shear no shear shear (with filtration) no shear (with filtration)

(s)

100 101 102 103 104 105

g(1) (

)0.0

0.2

0.4

0.6

0.8

1.0

shear no shear

time (s)

1e+0 1e+1 1e+2 1e+3 1e+4 1e+5 1e+6

g(1) (

)

0.0

0.2

0.4

0.6

0.8

1.0

shearno shear

M/T: 1 mg/ml M/T: 3 mg/ml, no filtration M/C: 3 mg/ml, no filtration

wavelength (nm)

550 600 650 700 750 800

inte

nsi

ty (

a.u

.)

0

20

40

60

80

10 mg/ml (shear)10 mg/ml (no shear) 5 mg/ml (shear)5 mg/ml (no shear) 3 mg/ml (shear) 3 mg/ml (no shear)1 mg/ml (shear) 1 mg/ml (no shear)

wavelength (nm)

550 600 650 700 750 800

inte

nsi

ty (

a.u

.)

0

20

40

60

80

1mgml (shear) 1mgml (no shear) 3mgml (shear)3mgml (no shear) 5mgml (shear) 5mgml (no shear) 10mgml (shear) 10mgml (no shear)

M/TM/C

In situ rheological/flow turbidity measuring apparatus

1ln (1)

: transmittance

: the path length of light passed through the

sample

T TL

T

L

(2)

: number of scattering centers

: total light energy scattered by one sphere

T sca

sca

NC

N

C

2

2

Using Mie theory and assumed spherical

scattering centers to simply analysis

(3)

: scattering efficiency

: Mie radius

22

sca sca

sca

sca

C Q a

Q

a

Q n 2 2

1

1 (4)

i ii

a b

Derived specific turbidity representation equation

Specific turbidity measuring theory

2 2

21

1

1

2

22 1

: Ricatti-Bessel function

: Hankel function

2

: wave length of incident l

sca i ii

i i i ii

i i i i

i n i ii

i i i i

i

i

Q n a b

m m ma

m m m

m m mb

m m m

x

x

n a

nm

n

1

2

ight

: refractive index of scattering center

: refractive index of medium

n

n

sca3 (5)

2

: specific turbidity

: density of scattering sphere

: concentration

T

T

Q

c

c

cKerker, M., 1969, THE SCATTERIG OF LIGHT AND OTHER ELECTROMAGNETIC RADIATION, Academic Press, Inc., San Diego.

Heller, W., and W. J. Pangonis, “Theoretical Investigations on the Light Scattering of Colloidal Spheres. I. The Specific Turbidity,” J. Chem. Phys. 26, 498-506 (1956)

Liberatore, M. W., and A. J. McHugh, “Dynamics of shear-induced structure formation in high molecular weight aqueous solutions,” J. Non-Newton. Fluid 132, 45-52 (2005)

Plot figure of specific turbidity vs. Mie radius

Equation of fitting curve:

10.7588 32.30470.0687

0.3024 42.0251: specific turbidity

y: Mie radius

x xy x

x xx

So, quantity of Mie radius can get from equation of fitting curve.

Experimental design and procedure:

DLSIn-situ rheological/flow turbidity measurement

Use DLS to measure hydrodynamic radius before shearing.

Compared Mie radius with Rh by two so different theory.

Under shear flow 10 min

Shear rate ： 60 [s-1]

Flow rested 15 min

Under shear flow 10 min

Shear rate ： 151~2,800 [s-

1]Flow rested 15 min

Altered shear rate

Under shear flow 10 min

Shear rate ： 60 [s-1]

Flow rested 15 min

Under shear flow 10 min

Shear rate ： 151~2,800 [s-

1]Flow rested 15 min

Ru

n2R

un1

Altered shear rate

MEH-PPV/DOP Sample

Main ideal is changed experiment factors of conc. and aging time, to observe the influence of two factors on aggregated properties.

Conc. [mg/ml]

0.02 0.3 1.0 3.0

Aging time

W/o aging 2 days aging

Experiment factors setting

The run1 is observed the behaviors while samples under various shear flow field

The run2 is observed the behaviors while samples experienced high shear flow field

Specific turbidity signal at various shear rate (w/o aging)0.02 mg/ml 0.3 mg/ml 1.0 mg/ml 3.0 mg/ml

Summary of specific turbidity (w/o aging)

At the lowest concentration, i.e., 0.02 mg/ml, the fluctuation in specific turbidity was noticed to be very large, suggesting that the aggregation state is unstable.

The specific turbidity decreased with increased sample concentration.

In both shearing and relaxation region, the specific turbidity of 0.3 mg/ml and 1.0 mg/ml sample solutions were lower than those before the shearing treatment.

Specific turbidity signal at various shear rate (2 days aging)0.02 mg/ml 0.3 mg/ml 1.0 mg/ml 3.0 mg/ml

Summary of specific turbidity (2 days aging)

Under sample with 2 days aging, the qualitative trends are the same as sample w/o aging.

Signal fluctuation of the 0.3 mg/ml sample solution is very large in the relaxation region. Suggesting that the aggregation state become unstable after shearing treatment.

The effect of concentration on aggregation properties

W/o aging 2 days ageing

Summary of the effect of concentration

With or without 2 days aging, Mie radius and increased with decreased sample concentration.

sp c

The influence of aging on aggregated properties0.02 mg/ml 0.3 mg/ml

1.0 mg/ml 3.0 mg/ml

Shear thinningMax.

Summary of aging influence

All concentration samples have the same trend, the Mie radius and increased while sample with aging.

The 3.0 mg/ml sample solution shows shear-thinning behavior whether sample w/o aging or with 2 days aging.

sp c

Comparison of results from flow turbidity and DLS measurements

Aging effect Conc.

Mie radius from specific turbidity

Rh from dynamic light scattering

Before shearing Before shearing

W/o aging

0.02 mg/ml 106.58 205.64

0.3 mg/ml 54.87 62.40

1.0 mg/ml 53.05 58.33

3.0 mg/ml 44.92 56.34

Aged 2 days

0.02 mg/ml 118.13 225.74

0.3 mg/ml 57.42 63.46

1.0 mg/ml 50.85 52.32

3.0 mg/ml 45.51 51.12

Good agreement was founded between the results from both measurements.

The Mie radius was differed from Rh in low concentration, 0.02 mg/ml.

Conclusion

The aggregation properties of MEH-PPV solution precursor solution, as they highly depend on sample concentration and sample with or w/o aging.

The results obtained from in-situ rheological/flow turbidity measurements and dynamic light scattering have great consistence.