Application of RHC to Nanostructured Polymer Systems Guy Van Assche, Jun Zhao, Nicolaas-Alexander...

Application of RHC

to Nanostructured Polymer Systems

Guy Van Assche, Jun Zhao, Nicolaas-Alexander Gotzen,

Nick Watzeels, Hans E. Miltner, Bruno Van Mele

Vrije Universiteit Brussel (VUB)

Research Unit for Physical Chemistry and Polymer Science

Department Materials and Chemistry

Faculty of Engineering

with the support of TA Instruments, FWO-Vlaanderen, Universiteit Hasselt

NATAS 2009Sept 20-23, 2009, Lubbock, Texas, USA

2

Outline

• Introduction RHC

• Results and discussion– Polymer-fullerene blends for solar cells– Crystallization kinetics of PCL nanocomposites– Crystallization and melting in iPP nanocomposites

• Conclusions

3

Introduction RHC

• Project RHC– Introduced at the 2007 NATAS meeting– Design, fabrication and subsequent evaluation of rapid-scanning DSC technology– For operation at high scanning rates, up to 2000 K/min in heating, similar in cooling– Retain ease of use and sample preparation of conventional DSC

→ DSC with Tzero™ technology but about 10x smaller ; heating by light (TGA Q5000)

– Four beta units were manufactured and delivered in june and november 2008

4

Introduction RHC

5

Introduction RHC – Performance and calibration

• Performance– Heat at 1500 K/min to 225°C– Cool at 1000 K/min to 75°C

– Switch to Neon for faster heating

• Calibration– Tzero™ calibration

• Empty furnace + Sapphire

– Indium– Calibrate at desired rate

• Shift ca. 2.5°C at 1000 K/min

-2000

-1000

0

1000

2000

Der

iv. T

zero

Tem

pera

ture

(°C

/min

)

-200 -100 0 100 200 300 400Temperature (°C)

HeatingProfileNeon.001––––––– CoolingProfileHelium.001––––––– HeatingProfileHelium.002–––––––

Universal V4.1D TA Instruments

10 K/min

20 K/min

50 K/min

100 K/min

500 K/min

200 K/min

1000 K/min

-80

-60

-40

-20

0

He

at F

low

T4

P (

W/g

)

140 150 160 170 180 190Temperature (°C)Exo Up Universal V4.1D TA Instruments

156.0

157.0

158.0

159.0

0 500 1000

Heating rate in K/min

Te

mp

era

ture

in °

C

6

Introduction RHC – Performance and calibration

• Performance– Heat at 1500 K/min to 225°C– Cool at 1000 K/min to 75°C

– Switch to Neon for faster heating

• Calibration– Tzero™ calibration

• Empty furnace + Sapphire

– Indium– Calibrate at desired rate

– Verification four samples• 156.60 °C ± 0.13 °C

• 28.93 J/g ± 0.21 J/g

158.37°C

156.53°C29.19J/g

158.23°C

156.50°C28.89J/g

158.72°C

156.78°C28.68J/g

158.40°C

156.58°C28.97J/g

-60

-40

-20

0

20

Hea

t Flo

w T

4P (

W/g

)

130 140 150 160 170 180 190Temperature (°C)Exo Up Universal V4.1D TA Instruments

-2000

-1000

0

1000

2000

Der

iv. T

zero

Tem

pera

ture

(°C

/min

)

-200 -100 0 100 200 300 400Temperature (°C)

HeatingProfileNeon.001––––––– CoolingProfileHelium.001––––––– HeatingProfileHelium.002–––––––

Universal V4.1D TA Instruments

7

Outline



• Conclusions

8

Polymer-fullerene blends for solar cells

• Bulk heterojunction solar cellsDonor: conducting polymer

Acceptor: fullerene

Photovoltaic process:Photon absorption → exciton generation

Diffusion to interface → exciton dissociation

Generated + and – charges flow to electrodes

Need co-continuous phase separated morphology

with ca. 10 nm dimension

Sn

O

O n

P3HT MDMO-PPV

PCBM

Sariciftci NS, Smilowitz L, Heeger AJ, Wudl F, Science, 1992, 258, 1474

Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ, Science, 1995, 270, 1789

9

Polymer-fullerene blends for solar cells - Aim

• Bulk heterojunction solar cellsDonor: conducting polymer

Acceptor: fullerene

Co-continuous phase separated morphology

with ca. 10 nm dimension

MDMO-PPV / PCBM at 110°C:Growth crystalline PCBM domains

Reduction efficiency within hours

Study phase formation processes

and state diagram to understand

morphology formation and stability

S. Bertho et al., Solar Energy Materials & Solar Cells 92 (2008) 753–760

O

O n

MDMO-PPV PCBM

1:4

110°C

2 µm

10

Polymer-fullerene blends for solar cells - Materials

• MaterialsDonor: P3HT (Merck)

MDMO-PPV (Merck)

High Tg-PPV (Merck)

Acceptor: PCBM (Solenne)

Blends drop-cast from chlorobenzene

• InstrumentsTA Instruments Q2000 Tzero DSC with MDSC option

DSC: 5 mg, 10 K/min

heat-cool-heat

MTDSC: 5 mg, 2.5 K/min, modulation 0.5 K / 60 s

heat-quench-heat

TA Instruments RHC

DSC: 0.5 mg, 500 K/min

heat-cool-heat

Calibration: T-zero calibration with sapphire, Indium for T and HF

SP3HT

n

O

OMDMO-PPV

n

O

O

PCBM

OR'

OC10

OMe

OC10ORRO

x y z

n

High Tg-PPV

11

Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMDSC results

• MDMO-PPV / PCBMMDMO-PPV:amorphous Tg ca. 25 - 50°C

PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C

Crystallisation retarded in presence of MDMO-PPV

Formation nano-morphology by crystallization PCBM + …

To stabilise nano-morphology, a glassy amorphous phase is desirable.

Tg of amorphous phase in blends? Tg of amorphous PCBM?

1st cooling 2nd heating

MDMO-PPVTg

CrystallisationPCBM

Tg MDMO-PPV

MeltingPCBM

12

Polymer-fullerene blends for solar cells – pure PCBMMTDSC and RHC results

• Pure PCBMRHC: Nearly completely amorphous, Tg ca. 130°C,

start cold-crystallization near 225°C, Tm ca. 280°C

MTDSC: not fully amorphous after in situ quench (avoid oxid. degradation), Tg ca. 130°C

Tg PCBM > Tg MDMO-PPV → Crystallization PCBM → Tg remaining amorphous phase ↓

Measure Tg of in situ quenched amorphous homogeneous blends in RHC

RHC: 2nd heating at 500 K/minafter in situ quench PCBM

Cold-cryst.

Melting

Tg

Cold-cryst.

PCBM

MTDSC: 2nd heating at 2.5 K/minafter in situ quench

MeltingTg

Cp

13

Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMMTDSC and RHC results

• MDMO-PPV:PCBM 1:4 or 80 wt% PCBMRHC: 2 Tg’s phase separated in liquid state

MTDSC: indications for 2 Tg’s, S/N worse

At 70-90 wt% PCBM double Tg is observed using RHC

→ Indication for phase separation in liquid state

→ Explains coarser, micrometer-sized morphologies found in this region

-100 0 100 200 300

1.5

2.0

2.5

3.0

3.5

50 100 150

0.002

0.004

0.006

Double Tg

Figure 14a MTDSC: 2nd (heating after quench),

2.5 K min-1, +/- 0.5 K per 60 s

App

aren

t sp

ecifi

c he

at c

apac

ity, c

papp (

J g-1

K-1)

Temperature, T (oC)

MDMO-PPV/PCBM

fw

PCBM, wt % 80.1

MTDSC: 2nd heating at 2.5 K/min

Cp

dCp/dT

RHC: 2nd heating at 500 K/minderiv.

14

Polymer-fullerene blends for solar cells – State diagrams

• Phase separation in liquid state:

- MDMO-PPV, High-Tg-PPV: Phase separate between 70 wt% and 90 wt% PCBM

- P3HT: Single Tg for each composition

• Long-term stability: compare Tg and max. operation temperature 80 °C

In range of optimal solar cell efficiency (50 wt% and 80 wt% PCBM)

– P3HT and MDMO-PPV have Tg < 80 °C → poor long-term stability

– High-Tg-PPV has Tg slightly above 80 °C → expect better stability

Tg’s + melting and crystallizationGlass transitions

15

Isothermal crystallization kinetics of PCL nanocomposites



• Conclusions

16

Isothermal crystallization kinetics of PCL nanocomposites

• Nanocomposites– Poly(ε-caprolactone) (PCL): CAPA6500

• Tg = -65 °C, Tm = 60 °C

– Carbon nanotubes: Nanocyl 7000 MWCNT– Nanocomposites by extrusion

Debundling confirmed by rheometry and SEM

Study isothermal crystallization kinetics of PCL-based nanocompositesfor modelling the solidification extruded sheets

Mettler 821 DSC

DSC: 5 mg, cooling to Tiso at 50 K/min, calibrated at 10 K/min

TA Instruments RHC

DSC: ca. 0.5 mg, cooling to Tiso at 500 K/min, calibrated at 100 K/min

Calibration: T-zero calibration with sapphire, Indium for T and HFMeasurement: compensation on reference with Al

nO

O

17

Isothermal crystallization kinetics - PCL

-60

-40

-20

0

20

40

60

80

0 1 2 3 4 5 6 7

Time (min)

He

at

flo

w (

W/g

)

-150

-100

-50

0

50

100

150

Te

mp

era

ture

(°C

)• Temperature program:

– Stay isothermal at 70°C for 2 min, cooled down at 500 K/min to T iso

• Compensation: to reduce overshoot in heat flow– ca. 0.8 mg of aluminum in reference crucible– Heat flow overshoot measured at 60 °C – no crystallization– Overshoot ca. 0.2 W/g, to baseline level in ca. 0.5 min

-1.0

0.0

1.0

2.0

2.45 2.95 3.45 3.95 4.45 4.95

Time (min)

He

at

flo

w (

W/g

)

30 °C60 °C

18


• Crystallization kinetics:– Studied by RHC from 38 °C to 16°C– For crystallization taking less than 0.5 min

→ transient from scan-to-isothermal begins to interfere

→ at 16 °C maximum not reliable.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 1.0 2.0 3.0 4.0 5.0

Time (min)

He

at

flo

w (

W/g

)

26 °C

30 °C

38 °C

34 °C

0

2

4

6

8

10

12

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (min)

He

at

flo

w (

W/g

)

16 °C

20 °C

24 °C

19




→ at 16 °C maximum not reliable– 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 1.0 2.0 3.0 4.0 5.0

Time (min)

He

at

flo

w (

W/g

)

26 °C

30 °C

38 °C

34 °C

0

2

4

6

8

10

12

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (min)

He

at

flo

w (

W/g

)

16 °C

20 °C

24 °C

20

-5.0

-4.0

-3.0

-2.0

-1.0

0.2 0.4 0.6 0.8 1.0

Reduced temperature (-)

log

(v

(1

/s))

nucleationdiffusion

• Hoffman-LauritzeExpression for crystal growth rate

diffusion nucleation




→ at 16 °C maximum not reliable– 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation

– DSC + RHC: range of close to 3 orders of magnitude

*

exp exp go

c c

KUG G

R T T T Tf

RHC

DSC

21

Isothermal crystallization kinetics – PCL + Carbon Nanotubes

0.0

0.5

1.0

1.5

2.0

2.5

0.0 1.0 2.0 3.0 4.0 5.0

Time (min)

He

at

flo

w (

W/g

)

48 °C

50 °C

52 °C

51 °C

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (min)

He

at

flo

w (

W/g

)

44 °C

45 °C

47 °C

46 °C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 1.0 2.0 3.0 4.0 5.0

Time (min)

He

at

flo

w (

W/g

)

26 °C

30 °C

38 °C

34 °C

0

2

4

6

8

10

12

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (min)

He

at

flo

w (

W/g

)

16 °C

20 °C

24 °C

PCL + CNT PCL + CNT

PCL PCL

22

Isothermal crystallization kinetics - PCL + Carbon Nanotubes

• Influence carbon nanotubes:– Strong nucleating effect of CNT– Similar rates of crystallization as

pure PCL at 15 – 25 °C higher temperatures

or,

At same temperature ca. 300x faster

0.0

0.5

1.0

1.5

2.0

2.5

0.0 1.0 2.0 3.0 4.0 5.0

Time (min)

He

at

flo

w (

W/g

)

48 °C

50 °C

52 °C

51 °C

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time (min)

He

at

flo

w (

W/g

)

44 °C

45 °C

47 °C

46 °C

-5.0

-4.0

-3.0

-2.0

-1.0

0.2 0.4 0.6 0.8 1.0

Reduced temperature (-)

log

(v

(1

/s))

23

Crystallization and melting in iPP-nanocomposites



• Conclusions

24


• Crystallization of iPP and iPP+CNT– CNT act as nucleating agent

→ iPP + CNT crystallizes at T+15 °C

→ Expect iPP + CNT melt at higher T

- XRD: iPP w/o CNT: α—phase

- Melting of iPP and iPP+CNT– Heating of in situ quenched samples

– At conventional low rate: iPP melts at higher T than iPP +

CNT ???

– Cause:

During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β

– At high rate: iPP melts at lower T (ok)

CNT result in structure that hinders recrystallization for iPP+CNT

Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762

Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085

iPP + CNT

iPP

25


• Crystallization of iPP and iPP+CNT– CNT act as nucleating agent

→ iPP + CNT crystallizes at T+15 °C

→ Expect iPP + CNT melt at higher T

- XRD: iPP w/o CNT: α—phase

- Melting of iPP and iPP+CNT– Heating of in situ quenched samples

– At conventional low rate: iPP melts at higher T than iPP +

CNT ???

– Cause:

During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β

– At high rate: iPP melts at lower T (ok)

CNT strongly nucleate PCL, creating a transcrystalline structure that hinders recrystallization into the β-phase

Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762

Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085

TEM: Transcrystalline interphase around CNTJ. Loos (TU Eindhoven, The Netherlands)

Sketch for possible nucleation mechanism

26

• Phase behavior of photovoltaic blends– RHC: Faster in situ quenching – important if oxidative degradation occurs in melt

– Glass transition of amorphous PCBM

– Double glass transitions in some blends indicate phase separation in melt

• Isothermal crystallization in PCL and its nanocomposites– RHC: Faster cooling and faster response

– Processes that take 30 s or more can be studied

– Extension of temperature range that can be studied, further extension by chip calorimetry and microcalorimetry

• Crystallization and melting in iPP and its nanocomposites– RHC: Cooling and heating at higher rates can suppress (slower) kinetic events

– Recrystallization of iPP is hindered in presence of CNT, formation of a transcrystalline interphase

• FWO-Vlaanderen (Belgium), TA Instruments (Delaware, USA) and OZR-VUB are acknowledged for their support

Conclusions

27

Thank you

28

Polymer-fullerene blends for solar cells – P3HT / PCBMDSC results

• P3HT / PCBMP3HT: semi-crystalline Tg ca. 0 - 25°C, Tm ca. 210°C, Tc ca. 180°C

PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C

For both P3HT and PCBM, crystallisation retarded in presence of second component

Formation nano-morphology by dual crystallization

1st cooling 2nd heating

P3HTTg

CrystallisationPCBM

P3HTTg Melting

MeltingPCBM

Crystallization

29

Polymer-fullerene blends for solar cells – pure PCBMMTDSC on sample aged at 103°C for 4000 min

Application of RHC to Nanostructured Polymer Systems Guy Van Assche, Jun Zhao, Nicolaas-Alexander...

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